diff --git a/.env.example b/.env.example
index e9a6df142..565ac4da3 100644
--- a/.env.example
+++ b/.env.example
@@ -33,6 +33,12 @@
 #     ANTHROPIC_API_KEY=sk-ant-your-key-here
 #     ANTHROPIC_MODEL=claude-sonnet-4-5              (optional)
 #     ANTHROPIC_BASE_URL=https://api.anthropic.com   (optional)
+#     ANTHROPIC_AUTH_TOKEN=your-provider-token       (custom Bearer endpoints)
+#
+#   Option 1b — Custom Anthropic-compatible API (Bearer auth):
+#     ANTHROPIC_BASE_URL=https://your-provider.example
+#     ANTHROPIC_AUTH_TOKEN=your-provider-token
+#     ANTHROPIC_MODEL=your-model-name
 #
 #   Option 2 — OpenAI:
 #     CLAUDE_CODE_USE_OPENAI=1
diff --git a/docs/advanced-setup.md b/docs/advanced-setup.md
index 59a426e35..9fcb0c330 100644
--- a/docs/advanced-setup.md
+++ b/docs/advanced-setup.md
@@ -409,6 +409,26 @@ already present as dev dependencies, so source/dev builds need no extra steps.
 
 ## Environment Variables
 
+### Custom (Anthropic-compatible) APIs
+
+For an endpoint that accepts Anthropic's native Messages API, set its base URL,
+Bearer token, and model directly. Do not set `CLAUDE_CODE_USE_OPENAI`; that
+selects the OpenAI-compatible transport instead.
+
+```bash
+export ANTHROPIC_BASE_URL=https://anthropic-proxy.example
+export ANTHROPIC_AUTH_TOKEN=your-provider-token
+export ANTHROPIC_MODEL=your-model-name
+openclaude
+```
+
+`ANTHROPIC_AUTH_TOKEN` is sent as `Authorization: Bearer ...`. The
+`/provider` → `Add provider` menu uses that Bearer-token setup as **Custom
+(Anthropic-compatible)**, including optional extra request headers. For a
+directly configured endpoint that instead requires Anthropic's native
+`x-api-key` authentication, set `ANTHROPIC_API_KEY` in place of the Bearer
+token; do not set both credentials.
+
 | Variable | Required | Description |
 |----------|----------|-------------|
 | `CLAUDE_CODE_USE_OPENAI` | OpenAI-compatible only | Set to `1` to enable the OpenAI-compatible provider path |
diff --git a/docs/integrations/overview.md b/docs/integrations/overview.md
index 8e1b0ba79..fa28a55b9 100644
--- a/docs/integrations/overview.md
+++ b/docs/integrations/overview.md
@@ -198,6 +198,6 @@ Important compatibility surfaces include:
 Contributor docs should describe these as compatibility bridges, not as the
 primary architecture.
 
-Preset ordering pins `anthropic` first, derives the middle entries from preset
-descriptions with standard alphanumeric sorting, and pins `custom` last
-automatically.
+Preset ordering pins `gitlawb-opengateway` first, derives the middle entries from preset
+descriptions with standard alphanumeric sorting, and pins the custom presets
+last: `custom` followed by `custom-anthropic`.
diff --git a/src/components/Feedback.tsx b/src/components/Feedback.tsx
index 41a433e89..6c2d63046 100644
--- a/src/components/Feedback.tsx
+++ b/src/components/Feedback.tsx
@@ -19,7 +19,10 @@ import { env } from '../utils/env.js';
 import { type GitRepoState, getGitState, getIsGit } from '../utils/git.js';
 import { getAuthHeaders, getUserAgent } from '../utils/http.js';
 import { getInMemoryErrors, logError } from '../utils/log.js';
-import { getAPIProvider } from '../utils/model/providers.js';
+import {
+  getAPIProvider,
+  isFirstPartyAnthropicBaseUrl,
+} from '../utils/model/providers.js';
 import { isEssentialTrafficOnly } from '../utils/privacyLevel.js';
 import { jsonRedactor, redactJsonLines, redactSensitiveInfo } from '../utils/redaction.js';
 import { extractTeammateTranscriptsFromTasks, getTranscriptPath, loadAllSubagentTranscriptsFromDisk, MAX_TRANSCRIPT_READ_BYTES } from '../utils/sessionStorage.js';
@@ -488,7 +491,7 @@ async function submitFeedback(data: FeedbackData, signal?: AbortSignal): Promise
   try {
     // Third-party providers should not post feedback to Anthropic, but they
     // should still reach the done state so users can open a GitHub issue draft.
-    if (getAPIProvider() !== 'firstParty') {
+    if (getAPIProvider() !== 'firstParty' || !isFirstPartyAnthropicBaseUrl()) {
       return {
         success: true,
         issueDraftOnly: true
diff --git a/src/components/FeedbackSurvey/submitTranscriptShare.ts b/src/components/FeedbackSurvey/submitTranscriptShare.ts
index c9f691105..03436c21c 100644
--- a/src/components/FeedbackSurvey/submitTranscriptShare.ts
+++ b/src/components/FeedbackSurvey/submitTranscriptShare.ts
@@ -5,6 +5,7 @@ import { checkAndRefreshOAuthTokenIfNeeded } from '../../utils/auth.js'
 import { logForDebugging } from '../../utils/debug.js'
 import { errorMessage } from '../../utils/errors.js'
 import { getAuthHeaders, getUserAgent } from '../../utils/http.js'
+import { isFirstPartyAnthropicProvider } from '../../utils/model/providers.js'
 import { normalizeMessagesForAPI } from '../../utils/messages.js'
 import {
   extractAgentIdsFromMessages,
@@ -31,6 +32,9 @@ export async function submitTranscriptShare(
   trigger: TranscriptShareTrigger,
   appearanceId: string,
 ): Promise<TranscriptShareResult> {
+  if (!isFirstPartyAnthropicProvider()) {
+    return { success: false }
+  }
   try {
     logForDebugging('Collecting transcript for sharing', { level: 'info' })
 
diff --git a/src/components/LogoV2/LogoV2.tsx b/src/components/LogoV2/LogoV2.tsx
index 4fb51255f..52b5d6dee 100644
--- a/src/components/LogoV2/LogoV2.tsx
+++ b/src/components/LogoV2/LogoV2.tsx
@@ -43,7 +43,7 @@ import { useShowOverageCreditUpsell, incrementOverageCreditUpsellSeenCount, crea
 import { plural } from '../../utils/stringUtils.js';
 import { useAppState } from '../../state/AppState.js';
 import { getEffortSuffix } from '../../utils/effort.js';
-import { getAPIProvider } from '../../utils/model/providers.js';
+import { isFirstPartyAnthropicProvider } from '../../utils/model/providers.js';
 import { useMainLoopModel } from '../../hooks/useMainLoopModel.js';
 import { renderModelSetting } from '../../utils/model/model.js';
 // Stubs: internal-only startup notices not included in this open snapshot
@@ -58,7 +58,7 @@ const LEFT_PANEL_MAX_WIDTH = 50;
 export function LogoV2() {
   const $ = _c(94);
   const activities = getRecentActivitySync();
-  const showAccountIdentity = getAPIProvider() === 'firstParty';
+  const showAccountIdentity = isFirstPartyAnthropicProvider();
   const username = showAccountIdentity ? getGlobalConfig().oauthAccount?.displayName ?? "" : "";
   const {
     columns
diff --git a/src/components/ProviderManager.test.tsx b/src/components/ProviderManager.test.tsx
index dc045137e..be4bc69a2 100644
--- a/src/components/ProviderManager.test.tsx
+++ b/src/components/ProviderManager.test.tsx
@@ -111,7 +111,7 @@ async function waitForCondition(
 
 // Provider list is sorted from generated preset metadata by description, with
 // Gitlawb Opengateway pinned first, Anthropic second, Codex OAuth injected
-// after DeepSeek, and Custom always pinned last. Keep the target-by-label
+// after DeepSeek, and the custom endpoints always pinned last. Keep the target-by-label
 // indirection here so
 // these tests survive future list edits without hardcoding raw key counts.
 //
@@ -154,7 +154,8 @@ const PRESET_ORDER = [
   'Xiaomi MiMo',
   'Xiaomi MiMo (Token Plan)',
   'Z.AI - GLM Coding Plan',
-  'Custom',
+  'Custom (OpenAI-compatible)',
+  'Custom (Anthropic-compatible)',
 ] as const
 
 async function navigateToPreset(
@@ -226,6 +227,17 @@ function mockProviderProfilesModule(options?: {
         }
       }
 
+      if (preset === 'custom-anthropic') {
+        return {
+          provider: 'custom-anthropic',
+          name: 'Custom (Anthropic-compatible)',
+          baseUrl: 'https://anthropic-proxy.example',
+          model: 'claude-sonnet-4-6',
+          apiKey: '',
+          requiresApiKey: true,
+        }
+      }
+
       if (preset === 'azure-openai') {
         return {
           provider: 'azure-openai',
@@ -663,7 +675,7 @@ test('ProviderManager shows API mode picker for custom OpenAI-compatible provide
       frame.includes('Choose provider preset'),
     )
 
-    await navigateToPreset(mounted.stdin, 'Custom')
+    await navigateToPreset(mounted.stdin, 'Custom (OpenAI-compatible)')
     mounted.stdin.write('\r')
     await waitForFrameOutput(mounted.getOutput, frame =>
       frame.includes('Create provider profile') &&
@@ -689,6 +701,57 @@ test('ProviderManager shows API mode picker for custom OpenAI-compatible provide
   }
 })
 
+test('ProviderManager offers a token field for custom Anthropic-compatible providers', async () => {
+  mockProviderManagerDependencies(() => undefined, async () => undefined)
+
+  const nonce = `${Date.now()}-${Math.random()}`
+  const { ProviderManager } = await import(`./ProviderManager.js?ts=${nonce}`)
+  const mounted = await mountProviderManager(ProviderManager)
+
+  try {
+    await waitForFrameOutput(mounted.getOutput, frame =>
+      frame.includes('Provider manager'),
+    )
+    mounted.stdin.write('\r')
+    await waitForFrameOutput(mounted.getOutput, frame =>
+      frame.includes('Choose provider preset'),
+    )
+    await navigateToPreset(mounted.stdin, 'Custom (Anthropic-compatible)')
+    mounted.stdin.write('\r')
+    await waitForFrameOutput(mounted.getOutput, frame => frame.includes('Provider name'))
+    mounted.stdin.write('\r')
+    await waitForFrameOutput(mounted.getOutput, frame => frame.includes('Base URL'))
+    mounted.stdin.write('\r')
+    await waitForFrameOutput(mounted.getOutput, frame => frame.includes('Default model'))
+    mounted.stdin.write('\r')
+
+    const output = await waitForFrameOutput(mounted.getOutput, frame =>
+      frame.includes('Credential') && frame.includes('Anthropic-compatible API'),
+    )
+    expect(output).not.toContain('API mode')
+    mounted.stdin.write('\r')
+    const requiredOutput = await waitForFrameOutput(mounted.getOutput, frame =>
+      frame.includes('Credential is required.'),
+    )
+    expect(requiredOutput).toContain('Credential is required.')
+    mounted.stdin.write('proxy-token')
+    mounted.stdin.write('\r')
+    const headersOutput = await waitForFrameOutput(mounted.getOutput, frame =>
+      frame.includes('Custom headers'),
+    )
+    expect(headersOutput).toContain('Extra non-auth request headers')
+    mounted.stdin.write('\r')
+    const placeholderError = await waitForFrameOutput(mounted.getOutput, frame =>
+      frame.includes('Base URL must be a real Anthropic-compatible endpoint.'),
+    )
+    expect(placeholderError).toContain(
+      'Base URL must be a real Anthropic-compatible endpoint.',
+    )
+  } finally {
+    await mounted.dispose()
+  }
+})
+
 test('ProviderManager keeps full setup flow for presets with placeholder endpoint defaults', async () => {
   mockProviderManagerDependencies(() => undefined, async () => undefined)
 
diff --git a/src/components/ProviderManager.tsx b/src/components/ProviderManager.tsx
index 7150d08e0..63326dd84 100644
--- a/src/components/ProviderManager.tsx
+++ b/src/components/ProviderManager.tsx
@@ -14,6 +14,7 @@ import {
   readCodexCredentialsAsync,
 } from '../utils/codexCredentials.js'
 import { isBareMode, isEnvTruthy } from '../utils/envUtils.js'
+import { isFirstPartyAnthropicBaseUrlForEnv } from '../utils/anthropicBaseUrl.js'
 import {
   parseProfileCustomHeadersInput,
   serializeProfileCustomHeaders,
@@ -293,7 +294,11 @@ function presetToDraft(preset: ProviderPreset): ProviderDraft {
 }
 
 function isSetupPlaceholder(value: string): boolean {
-  return /\bYOUR[-_\s]/i.test(value) || /<[^>]+>/.test(value)
+  return (
+    /\bYOUR[-_\s]/i.test(value) ||
+    /<[^>]+>/.test(value) ||
+    /:\/\/[^/]+\.example(?:\/|$)/i.test(value)
+  )
 }
 
 function canUseStreamlinedPresetFlow(draft: ProviderDraft): boolean {
@@ -905,6 +910,16 @@ export function ProviderManager({ mode, onDone }: Props): React.ReactNode {
   const currentStep = formSteps[formStepIndex] ?? formSteps[0] ?? FORM_STEPS[0]
   const currentStepKey = currentStep.key
   const currentValue = draft[currentStepKey]
+  const displayStep =
+    draftProvider === 'custom-anthropic' && currentStepKey === 'apiKey'
+      ? {
+          ...currentStep,
+          label: 'Credential',
+          placeholder: 'Credential for this endpoint',
+          helpText: 'The custom profile stores this as an Authorization Bearer token.',
+          optional: false,
+        }
+      : currentStep
 
   // Memoize menu options to prevent unnecessary re-renders when navigating
   // the select menu. Without this, each arrow key press creates a new options
@@ -1598,7 +1613,11 @@ export function ProviderManager({ mode, onDone }: Props): React.ReactNode {
       return
     }
 
-    if (preset === 'custom' || !canUseStreamlinedPresetFlow(nextDraft)) {
+    if (
+      preset === 'custom' ||
+      preset === 'custom-anthropic' ||
+      !canUseStreamlinedPresetFlow(nextDraft)
+    ) {
       setScreen('form')
       return
     }
@@ -1629,6 +1648,17 @@ export function ProviderManager({ mode, onDone }: Props): React.ReactNode {
     provider: ProviderProfile['provider'] = draftProvider,
     profileId: string | null = editingProfileId,
   ): void {
+    if (
+      provider === 'custom-anthropic' &&
+      (isSetupPlaceholder(nextDraft.baseUrl) ||
+        isFirstPartyAnthropicBaseUrlForEnv({
+          ANTHROPIC_BASE_URL: nextDraft.baseUrl,
+          USER_TYPE: process.env.USER_TYPE,
+        }))
+    ) {
+      setErrorMessage('Base URL must be a real Anthropic-compatible endpoint.')
+      return
+    }
     const routeId = resolveProviderEditorRouteId(provider, nextDraft.baseUrl)
     const supportsApiFormat = routeSupportsApiFormatSelection(routeId)
     const showsAuthHeader = routeShowsAuthHeader(routeId)
@@ -1908,8 +1938,8 @@ export function ProviderManager({ mode, onDone }: Props): React.ReactNode {
   function handleFormSubmit(value: string): void {
     const trimmed = value.trim()
 
-    if (!currentStep.optional && trimmed.length === 0) {
-      setErrorMessage(`${currentStep.label} is required.`)
+    if (!displayStep.optional && trimmed.length === 0) {
+      setErrorMessage(`${displayStep.label} is required.`)
       return
     }
 
@@ -2159,7 +2189,7 @@ export function ProviderManager({ mode, onDone }: Props): React.ReactNode {
         <Text color="remember" bold>
           {editingProfileId ? 'Edit provider profile' : 'Create provider profile'}
         </Text>
-        <Text dimColor>{currentStep.helpText}</Text>
+        <Text dimColor>{displayStep.helpText}</Text>
         <Text dimColor>
           Provider type:{' '}
           {getRouteProviderTypeLabel(resolveProfileRoute(draftProvider).routeId)}
@@ -2171,7 +2201,7 @@ export function ProviderManager({ mode, onDone }: Props): React.ReactNode {
           </Text>
         ) : null}
         <Text dimColor>
-          Step {formStepIndex + 1} of {formSteps.length}: {currentStep.label}
+          Step {formStepIndex + 1} of {formSteps.length}: {displayStep.label}
         </Text>
         {currentStepKey === 'apiFormat' ? (
           <Select
@@ -2216,7 +2246,7 @@ export function ProviderManager({ mode, onDone }: Props): React.ReactNode {
               onSubmit={handleFormSubmit}
               focus={true}
               showCursor={true}
-              placeholder={`${currentStep.placeholder}${figures.ellipsis}`}
+              placeholder={`${displayStep.placeholder}${figures.ellipsis}`}
               mask={
                 currentStepKey === 'apiKey' ||
                 currentStepKey === 'authHeaderValue'
diff --git a/src/integrations/anthropicProxies/custom.ts b/src/integrations/anthropicProxies/custom.ts
new file mode 100644
index 000000000..f5e70b2f5
--- /dev/null
+++ b/src/integrations/anthropicProxies/custom.ts
@@ -0,0 +1,45 @@
+import { defineAnthropicProxy } from '../define.js'
+
+// A generic user-configured Anthropic Messages API endpoint. Unlike the
+// first-party Anthropic preset, this route can use a provider-issued Bearer
+// token or native x-api-key authentication.
+export default defineAnthropicProxy({
+  id: 'custom-anthropic',
+  label: 'Custom (Anthropic-compatible)',
+  classification: 'anthropic-proxy',
+  defaultBaseUrl: 'https://anthropic-proxy.example',
+  defaultModel: 'claude-sonnet-4-6',
+  setup: {
+    requiresAuth: true,
+    authMode: 'token',
+    credentialEnvVars: ['ANTHROPIC_AUTH_TOKEN', 'ANTHROPIC_API_KEY'],
+    setupPrompt: 'Paste the credential for your Anthropic-compatible endpoint.',
+  },
+  envVarConfig: {
+    authTokenEnvVar: 'ANTHROPIC_AUTH_TOKEN',
+    baseUrlEnvVar: 'ANTHROPIC_BASE_URL',
+    modelEnvVar: 'ANTHROPIC_MODEL',
+  },
+  capabilities: {
+    supportsStreaming: true,
+    supportsFunctionCalling: true,
+    supportsVision: true,
+  },
+  transportConfig: {
+    kind: 'anthropic-proxy',
+    anthropicProxy: { supportsCustomHeaders: true },
+  },
+  usage: { supported: false },
+  preset: {
+    id: 'custom-anthropic',
+    description: 'Any Anthropic Messages API-compatible provider',
+    label: 'Custom (Anthropic-compatible)',
+    name: 'Custom (Anthropic-compatible)',
+    vendorId: 'anthropic',
+    apiKeyEnvVars: ['ANTHROPIC_AUTH_TOKEN', 'ANTHROPIC_API_KEY'],
+    baseUrlEnvVars: ['ANTHROPIC_BASE_URL'],
+    modelEnvVars: ['ANTHROPIC_MODEL'],
+    fallbackBaseUrl: 'https://anthropic-proxy.example',
+    fallbackModel: 'claude-sonnet-4-6',
+  },
+})
diff --git a/src/integrations/artifactGenerator.ts b/src/integrations/artifactGenerator.ts
index 694b9e3d2..41e65b47c 100644
--- a/src/integrations/artifactGenerator.ts
+++ b/src/integrations/artifactGenerator.ts
@@ -250,13 +250,18 @@ function compareProviderPresetEntries(
     return 1
   }
 
-  if (leftPreset === 'custom') {
+  // Keep the generic custom endpoints together at the end of the picker,
+  // with the Anthropic-native option after the OpenAI-compatible one.
+  if (leftPreset === 'custom-anthropic') {
     return 1
   }
-  if (rightPreset === 'custom') {
+  if (rightPreset === 'custom-anthropic') {
     return -1
   }
 
+  if (leftPreset === 'custom') return 1
+  if (rightPreset === 'custom') return -1
+
   const descriptionDelta = PRESET_DESCRIPTION_COLLATOR.compare(
     String(left.description),
     String(right.description),
diff --git a/src/integrations/compatibility.test.ts b/src/integrations/compatibility.test.ts
index 3c9267ff0..5431802f3 100644
--- a/src/integrations/compatibility.test.ts
+++ b/src/integrations/compatibility.test.ts
@@ -5,6 +5,7 @@ import {
   getGateway,
   getModelsForGateway,
   getVendor,
+  ORDERED_PROVIDER_PRESETS,
 } from './index.js'
 import {
   PRESET_VENDOR_MAP,
@@ -35,6 +36,7 @@ const EXPECTED_PRESETS = [
   'dashscope-cn',
   'dashscope-intl',
   'custom',
+  'custom-anthropic',
   'nvidia-nim',
   'minimax',
   'xai',
@@ -76,7 +78,9 @@ describe('compatibility mappings', () => {
 
       expect(route.vendorId).toBe(vendorId)
       expect(route.gatewayId).toBe(gatewayId)
-      expect(route.routeId).toBe(gatewayId ?? vendorId)
+      expect(route.routeId).toBe(
+        preset === 'custom-anthropic' ? 'custom-anthropic' : gatewayId ?? vendorId,
+      )
     }
   })
 
@@ -95,6 +99,24 @@ describe('compatibility mappings', () => {
     })
   })
 
+  test('Custom Anthropic is modeled as an Anthropic proxy', () => {
+    expect(routeForPreset('custom-anthropic')).toEqual({
+      vendorId: 'anthropic',
+      routeId: 'custom-anthropic',
+    })
+    expect(resolveProfileRoute('custom-anthropic')).toEqual({
+      vendorId: 'anthropic',
+      routeId: 'custom-anthropic',
+    })
+  })
+
+  test('keeps custom provider presets at the bottom of the add-provider list', () => {
+    expect(ORDERED_PROVIDER_PRESETS.slice(-2)).toEqual([
+      'custom',
+      'custom-anthropic',
+    ])
+  })
+
   test('Atlas Cloud gateway models do not resolve to NearAI-scoped descriptors', () => {
     const atlasModels = getModelsForGateway('atlas-cloud')
     expect(atlasModels.length).toBeGreaterThan(0)
diff --git a/src/integrations/descriptors.ts b/src/integrations/descriptors.ts
index ae9997def..5583069aa 100644
--- a/src/integrations/descriptors.ts
+++ b/src/integrations/descriptors.ts
@@ -85,6 +85,9 @@ export interface TransportConfig {
   kind: TransportKind
   headers?: Record<string, string>
   openaiShim?: OpenAIShimTransportConfig
+  anthropicProxy?: {
+    supportsCustomHeaders?: boolean
+  }
 }
 
 export interface CatalogTransportOverrides {
diff --git a/src/integrations/gateways/custom.ts b/src/integrations/gateways/custom.ts
index 551933335..314a57721 100644
--- a/src/integrations/gateways/custom.ts
+++ b/src/integrations/gateways/custom.ts
@@ -24,7 +24,7 @@ function getModelInfo(raw: unknown): Record<string, unknown> | undefined {
 
 export default defineGateway({
   id: 'custom',
-  label: 'Custom OpenAI-compatible',
+  label: 'Custom (OpenAI-compatible)',
   category: 'hosted',
   defaultModel: 'llama3.1:8b',
   supportsModelRouting: true,
@@ -42,8 +42,8 @@ export default defineGateway({
   preset: {
     id: 'custom',
     description: 'Any OpenAI-compatible provider',
-    label: 'Custom',
-    name: 'Custom OpenAI-compatible',
+    label: 'Custom (OpenAI-compatible)',
+    name: 'Custom (OpenAI-compatible)',
     apiKeyEnvVars: ['OPENAI_API_KEYS', 'OPENAI_API_KEY'],
     baseUrlEnvVars: ['OPENAI_BASE_URL', 'OPENAI_API_BASE'],
     modelEnvVars: ['OPENAI_MODEL'],
diff --git a/src/integrations/generated/integrationArtifacts.generated.ts b/src/integrations/generated/integrationArtifacts.generated.ts
index cb5731193..3446351ec 100644
--- a/src/integrations/generated/integrationArtifacts.generated.ts
+++ b/src/integrations/generated/integrationArtifacts.generated.ts
@@ -44,6 +44,7 @@ import gatewayOpenrouter from '../gateways/openrouter.js'
 import gatewayTogether from '../gateways/together.js'
 import gatewayVertex from '../gateways/vertex.js'
 import gatewayXiaomiMimoToken from '../gateways/xiaomi-mimo-token.js'
+import anthropicproxyCustom from '../anthropicProxies/custom.js'
 import brandClaude from '../brands/claude.js'
 import brandDeepseek from '../brands/deepseek.js'
 import brandFireworks from '../brands/fireworks.js'
@@ -82,7 +83,7 @@ import modelXiaomiMimo from '../models/xiaomi-mimo.js'
 
 export const VENDOR_DESCRIPTORS = [vendorAnthropic, vendorBankr, vendorDeepseek, vendorFireworks, vendorGemini, vendorMinimax, vendorMoonshot, vendorNearai, vendorOpenai, vendorVenice, vendorXai, vendorXiaomiMimo, vendorZai] as const satisfies readonly VendorDescriptor[]
 export const GATEWAY_DESCRIPTORS = [gatewayAimlapi, gatewayAtlasCloud, gatewayAtomicChat, gatewayAzureOpenai, gatewayBedrock, gatewayClinepass, gatewayCloudflare, gatewayCustom, gatewayDashscopeCn, gatewayDashscopeIntl, gatewayGithubEnterprise, gatewayGithub, gatewayGitlawbOpengateway, gatewayGroq, gatewayHicap, gatewayKimiCode, gatewayLmstudio, gatewayMistral, gatewayNvidiaNim, gatewayOllama, gatewayOpencodeGo, gatewayOpencode, gatewayOpenrouter, gatewayTogether, gatewayVertex, gatewayXiaomiMimoToken] as const satisfies readonly GatewayDescriptor[]
-export const ANTHROPIC_PROXY_DESCRIPTORS = [] as const satisfies readonly AnthropicProxyDescriptor[]
+export const ANTHROPIC_PROXY_DESCRIPTORS = [anthropicproxyCustom] as const satisfies readonly AnthropicProxyDescriptor[]
 export const BRAND_DESCRIPTORS = [brandClaude, brandDeepseek, brandFireworks, brandGemini, brandGlm, brandGpt, brandKimi, brandLlama, brandMinimax, brandMistral, brandNearai, brandNemotron, brandOpenaiCompatibleAlias, brandQwen, brandTencent, brandXai, brandXiaomiMimo] as const satisfies readonly BrandDescriptor[]
 export const MODEL_DESCRIPTOR_GROUPS = [modelClaude, modelDeepseek, modelFireworksMerged, modelGemini, modelGlm, modelGpt, modelKimi, modelLlama, modelMinimax, modelMistral, modelNearai, modelNemotron, modelOpenaiCompatibleAlias, modelOpencode, modelQwen, modelTencent, modelXai, modelXiaomiMimo] as const satisfies readonly (readonly ModelDescriptor[])[]
 export const MODEL_DESCRIPTORS = MODEL_DESCRIPTOR_GROUPS.flat() satisfies readonly ModelDescriptor[]
diff --git a/src/integrations/generated/integrationManifest.generated.ts b/src/integrations/generated/integrationManifest.generated.ts
index 34df06697..014e53eea 100644
--- a/src/integrations/generated/integrationManifest.generated.ts
+++ b/src/integrations/generated/integrationManifest.generated.ts
@@ -468,8 +468,8 @@ export const PROVIDER_PRESET_MANIFEST = [
     "vendorId": "openai",
     "gatewayId": "custom",
     "description": "Any OpenAI-compatible provider",
-    "label": "Custom",
-    "name": "Custom OpenAI-compatible",
+    "label": "Custom (OpenAI-compatible)",
+    "name": "Custom (OpenAI-compatible)",
     "apiKeyEnvVars": [
       "OPENAI_API_KEYS",
       "OPENAI_API_KEY"
@@ -482,6 +482,27 @@ export const PROVIDER_PRESET_MANIFEST = [
       "OPENAI_MODEL"
     ],
     "fallbackBaseUrl": "http://localhost:11434/v1"
+  },
+  {
+    "preset": "custom-anthropic",
+    "routeKind": "anthropic-proxy",
+    "routeId": "custom-anthropic",
+    "vendorId": "anthropic",
+    "description": "Any Anthropic Messages API-compatible provider",
+    "label": "Custom (Anthropic-compatible)",
+    "name": "Custom (Anthropic-compatible)",
+    "apiKeyEnvVars": [
+      "ANTHROPIC_AUTH_TOKEN",
+      "ANTHROPIC_API_KEY"
+    ],
+    "baseUrlEnvVars": [
+      "ANTHROPIC_BASE_URL"
+    ],
+    "modelEnvVars": [
+      "ANTHROPIC_MODEL"
+    ],
+    "fallbackBaseUrl": "https://anthropic-proxy.example",
+    "fallbackModel": "claude-sonnet-4-6"
   }
 ] as const satisfies readonly ProviderPresetManifestEntry[]
 export type ProviderPreset = (typeof PROVIDER_PRESET_MANIFEST)[number]['preset']
@@ -520,5 +541,6 @@ export const ORDERED_PROVIDER_PRESETS = [
   "xiaomi-mimo",
   "xiaomi-mimo-token",
   "zai",
-  "custom"
+  "custom",
+  "custom-anthropic"
 ] as const
diff --git a/src/integrations/index.test.ts b/src/integrations/index.test.ts
index dac233f05..66b203c92 100644
--- a/src/integrations/index.test.ts
+++ b/src/integrations/index.test.ts
@@ -37,6 +37,7 @@ describe('loaded registry validation', () => {
     expect(routeSupportsApiFormatSelection('minimax')).toBe(false)
     expect(routeSupportsAuthHeaders('minimax')).toBe(false)
     expect(routeSupportsCustomHeaders('minimax')).toBe(false)
+    expect(routeSupportsCustomHeaders('custom-anthropic')).toBe(true)
   })
 
   test('route catalogs do not duplicate defaultModel with catalog default flags', () => {
diff --git a/src/integrations/profileResolver.ts b/src/integrations/profileResolver.ts
index fb977e9bc..ddf5a3224 100644
--- a/src/integrations/profileResolver.ts
+++ b/src/integrations/profileResolver.ts
@@ -2,7 +2,7 @@
 // Resolves a stored profile.provider string to a descriptor-backed route.
 // This bridges legacy preset names, vendor ids, gateway ids, and custom strings.
 
-import { getGateway, getVendor } from './registry.js'
+import { getAnthropicProxy, getGateway, getVendor } from './registry.js'
 import { isProviderPreset, routeForPreset } from './compatibility.js'
 
 export type ResolvedProfileRoute = {
@@ -42,7 +42,13 @@ export function resolveProfileRoute(provider: string): ResolvedProfileRoute {
     }
   }
 
-  // 4. Safe fallback — OpenAI-compatible so the user can still interact,
+  // 4. Try Anthropic-native proxy id.
+  const anthropicProxy = getAnthropicProxy(provider)
+  if (anthropicProxy) {
+    return { vendorId: 'anthropic', routeId: anthropicProxy.id }
+  }
+
+  // 5. Safe fallback — OpenAI-compatible so the user can still interact,
   //    but the routeId makes it clear this is unrecognised.
   return { vendorId: 'openai', routeId: 'unknown-fallback' }
 }
diff --git a/src/integrations/routeMetadata.test.ts b/src/integrations/routeMetadata.test.ts
index 6b0883cdc..ac62a9f45 100644
--- a/src/integrations/routeMetadata.test.ts
+++ b/src/integrations/routeMetadata.test.ts
@@ -125,6 +125,64 @@ test('getRouteCredentialEnvVars keeps descriptor env vars and openai fallback fo
   ])
 })
 
+test('custom Anthropic credentials stay native and resolve to their proxy route', () => {
+  expect(getRouteCredentialEnvVars('custom-anthropic')).toEqual([
+    'ANTHROPIC_AUTH_TOKEN',
+    'ANTHROPIC_API_KEY',
+  ])
+  expect(
+    resolveActiveRouteIdFromEnv({
+      ANTHROPIC_BASE_URL: 'https://tenant.example/v1',
+      ANTHROPIC_MODEL: 'tenant-model',
+      ANTHROPIC_AUTH_TOKEN: 'tenant-token',
+    }),
+  ).toBe('custom-anthropic')
+
+  expect(
+    resolveActiveRouteIdFromEnv({
+      ANTHROPIC_BASE_URL: 'https://api.anthropic.com',
+      ANTHROPIC_MODEL: 'claude-sonnet-4-6',
+      ANTHROPIC_AUTH_TOKEN: 'first-party-token',
+    }),
+  ).toBe('anthropic')
+
+  expect(
+    resolveActiveRouteIdFromEnv({
+      CLAUDE_CODE_USE_OPENAI: '1',
+      OPENAI_BASE_URL: 'https://api.openai.com/v1',
+      OPENAI_API_KEY: 'openai-key',
+      ANTHROPIC_BASE_URL: 'https://tenant.example/v1',
+      ANTHROPIC_MODEL: 'tenant-model',
+      ANTHROPIC_AUTH_TOKEN: 'tenant-token',
+    }),
+  ).toBe('openai')
+
+  expect(
+    resolveActiveRouteIdFromEnv({
+      ANTHROPIC_BASE_URL: 'https://tenant.example/v1',
+      ANTHROPIC_MODEL: 'tenant-model',
+      ANTHROPIC_API_KEY: 'tenant-key',
+    }),
+  ).toBe('custom-anthropic')
+
+  expect(
+    resolveActiveRouteIdFromEnv({
+      ANTHROPIC_BASE_URL: 'https://tenant.example/v1',
+      ANTHROPIC_MODEL: 'tenant-model',
+      ANTHROPIC_API_KEY: 'tenant-key',
+      MINIMAX_API_KEY: 'ambient-minimax-key',
+    }),
+  ).toBe('custom-anthropic')
+
+  expect(
+    resolveActiveRouteIdFromEnv({
+      ANTHROPIC_BASE_URL: 'https://api.minimax.io/anthropic',
+      ANTHROPIC_MODEL: 'tenant-model',
+      ANTHROPIC_AUTH_TOKEN: 'tenant-token',
+    }),
+  ).toBe('custom-anthropic')
+})
+
 test('getRouteCredentialEnvVars omits the openai fallback for dedicatedCredentialsOnly routes', () => {
   expect(getRouteCredentialEnvVars('atlas-cloud')).toEqual([
     'ATLAS_CLOUD_API_KEY',
diff --git a/src/integrations/routeMetadata.ts b/src/integrations/routeMetadata.ts
index 1c1e76410..da2f1bc48 100644
--- a/src/integrations/routeMetadata.ts
+++ b/src/integrations/routeMetadata.ts
@@ -6,16 +6,19 @@ import type {
 } from './descriptors.js'
 import {
   ensureIntegrationsLoaded,
+  getAllAnthropicProxies,
   getAllGateways,
   getAllVendors,
   getGateway,
+  getAnthropicProxy,
   getVendor,
   resolveProfileRoute,
 } from './index.js'
 import { hasUsableOpenAICredential } from '../services/api/credentialPool.js'
 import { isEnvTruthy } from '../utils/envUtils.js'
+import { isFirstPartyAnthropicBaseUrlForEnv } from '../utils/anthropicBaseUrl.js'
 
-export type RouteDescriptor = GatewayDescriptor | VendorDescriptor
+export type RouteDescriptor = GatewayDescriptor | VendorDescriptor | import('./descriptors.js').AnthropicProxyDescriptor
 
 const TRANSPORT_KIND_PROVIDER_TYPE_LABELS: Partial<
   Record<TransportKind, string>
@@ -93,7 +96,7 @@ function normalizeHost(
 
 function getAllRoutes(): RouteDescriptor[] {
   ensureIntegrationsLoaded()
-  return [...getAllGateways(), ...getAllVendors()]
+  return [...getAllGateways(), ...getAllVendors(), ...getAllAnthropicProxies()]
 }
 
 function resolveKnownLocalRouteIdFromBaseUrl(baseUrl?: string): string | null {
@@ -129,7 +132,7 @@ export function getRouteDescriptor(
   routeId: string,
 ): RouteDescriptor | null {
   ensureIntegrationsLoaded()
-  return getGateway(routeId) ?? getVendor(routeId) ?? null
+  return getGateway(routeId) ?? getVendor(routeId) ?? getAnthropicProxy(routeId) ?? null
 }
 
 export function getRouteLabel(
@@ -829,7 +832,10 @@ export function routeSupportsCustomHeaders(
     return false
   }
 
-  return descriptor.transportConfig.openaiShim?.supportsAuthHeaders === true
+  return (
+    descriptor.transportConfig.openaiShim?.supportsAuthHeaders === true ||
+    descriptor.transportConfig.anthropicProxy?.supportsCustomHeaders === true
+  )
 }
 
 export function routeShowsAuthHeaderValue(routeId: string): boolean {
@@ -992,6 +998,26 @@ export function resolveActiveRouteIdFromEnv(
     return 'vertex'
   }
 
+  // A Bearer token explicitly selects the custom Anthropic proxy contract,
+  // even if the host also belongs to a known OpenAI-compatible route. Keep
+  // native x-api-key configurations on those known routes for compatibility.
+  const knownAnthropicRoute = resolveRouteIdFromBaseUrl(
+    processEnv.ANTHROPIC_BASE_URL,
+  )
+  if (
+    !isEnvTruthy(processEnv.CLAUDE_CODE_USE_OPENAI) &&
+    hasNonEmptyEnvValue(processEnv.ANTHROPIC_BASE_URL) &&
+    hasNonEmptyEnvValue(processEnv.ANTHROPIC_MODEL) &&
+    (hasNonEmptyEnvValue(processEnv.ANTHROPIC_AUTH_TOKEN) ||
+      hasNonEmptyEnvValue(processEnv.ANTHROPIC_API_KEY)) &&
+    !isFirstPartyAnthropicBaseUrlForEnv(processEnv) &&
+    (hasNonEmptyEnvValue(processEnv.ANTHROPIC_AUTH_TOKEN) ||
+      knownAnthropicRoute === 'custom-anthropic' ||
+      !knownAnthropicRoute)
+  ) {
+    return 'custom-anthropic'
+  }
+
   const envOnlyRouteId = resolveEnvOnlyProviderRouteId(processEnv)
   if (envOnlyRouteId) return envOnlyRouteId
 
diff --git a/src/main.tsx b/src/main.tsx
index bfb214e03..a7832be9b 100644
--- a/src/main.tsx
+++ b/src/main.tsx
@@ -58,6 +58,7 @@ import { clampUltracodeEffort, getInitialEffortSetting, parseEffortValue } from
 import { getInitialFastModeSetting, isFastModeEnabled, prefetchFastModeStatus, resolveFastModeStatusFromCache } from './utils/fastMode.js';
 import { applyConfigEnvironmentVariables } from './utils/managedEnv.js';
 import { createSystemMessage, createUserMessage } from './utils/messages.js';
+import { isFirstPartyAnthropicBaseUrl } from './utils/model/providers.js';
 import { getPlatform } from './utils/platform.js';
 import { getBaseRenderOptions } from './utils/renderOptions.js';
 import { getSessionIngressAuthToken } from './utils/sessionIngressAuth.js';
@@ -1286,10 +1287,12 @@ async function run(): Promise<CommanderCommand> {
       const fileSessionId = process.env.CLAUDE_CODE_REMOTE_SESSION_ID || getSessionId();
       const files = parseFileSpecs(fileSpecs);
       if (files.length > 0) {
-        // Use ANTHROPIC_BASE_URL if set (by EnvManager), otherwise use OAuth config
-        // This ensures consistency with session ingress API in all environments
+        // Session ingress credentials are only valid for the first-party Files API.
+        // A custom Anthropic endpoint must never receive this bearer token.
         const config: FilesApiConfig = {
-          baseUrl: process.env.ANTHROPIC_BASE_URL || getOauthConfig().BASE_API_URL,
+          baseUrl: isFirstPartyAnthropicBaseUrl()
+            ? process.env.ANTHROPIC_BASE_URL || getOauthConfig().BASE_API_URL
+            : getOauthConfig().BASE_API_URL,
           oauthToken: sessionToken,
           sessionId: fileSessionId
         };
diff --git a/src/migrations/migrateLegacyOpusToCurrent.ts b/src/migrations/migrateLegacyOpusToCurrent.ts
index 8e7181c61..46a146148 100644
--- a/src/migrations/migrateLegacyOpusToCurrent.ts
+++ b/src/migrations/migrateLegacyOpusToCurrent.ts
@@ -4,7 +4,7 @@ import {
 } from '../services/analytics/index.js'
 import { saveGlobalConfig } from '../utils/config.js'
 import { isLegacyModelRemapEnabled } from '../utils/model/model.js'
-import { getAPIProvider } from '../utils/model/providers.js'
+import { getAPIProvider, isFirstPartyAnthropicBaseUrl } from '../utils/model/providers.js'
 import {
   getSettingsForSource,
   updateSettingsForSource,
@@ -27,7 +27,7 @@ import {
  * project.
  */
 export function migrateLegacyOpusToCurrent(): void {
-  if (getAPIProvider() !== 'firstParty') {
+  if (getAPIProvider() !== 'firstParty' || !isFirstPartyAnthropicBaseUrl()) {
     return
   }
 
diff --git a/src/migrations/migrateSonnet1mToSonnet45.ts b/src/migrations/migrateSonnet1mToSonnet45.ts
index 233195912..a35cd415e 100644
--- a/src/migrations/migrateSonnet1mToSonnet45.ts
+++ b/src/migrations/migrateSonnet1mToSonnet45.ts
@@ -3,7 +3,9 @@ import {
   setMainLoopModelOverride,
 } from '../bootstrap/state.js'
 import { getGlobalConfig, saveGlobalConfig } from '../utils/config.js'
-import { getAPIProvider } from '../utils/model/providers.js'
+import {
+  isFirstPartyAnthropicProvider,
+} from '../utils/model/providers.js'
 import {
   getSettingsForSource,
   updateSettingsForSource,
@@ -24,7 +26,7 @@ import {
  * tracked by a completion flag in global config.
  */
 export function migrateSonnet1mToSonnet45(): void {
-  if (getAPIProvider() !== 'firstParty') {
+  if (!isFirstPartyAnthropicProvider()) {
     return
   }
 
diff --git a/src/migrations/migrateSonnet45ToSonnet46.ts b/src/migrations/migrateSonnet45ToSonnet46.ts
index bfbfcefe8..78ac60034 100644
--- a/src/migrations/migrateSonnet45ToSonnet46.ts
+++ b/src/migrations/migrateSonnet45ToSonnet46.ts
@@ -8,7 +8,7 @@ import {
   isTeamPremiumSubscriber,
 } from '../utils/auth.js'
 import { getGlobalConfig, saveGlobalConfig } from '../utils/config.js'
-import { getAPIProvider } from '../utils/model/providers.js'
+import { getAPIProvider, isFirstPartyAnthropicBaseUrl } from '../utils/model/providers.js'
 import {
   getSettingsForSource,
   updateSettingsForSource,
@@ -27,7 +27,7 @@ import {
  * Idempotent: only writes if userSettings.model matches a Sonnet 4.5 string.
  */
 export function migrateSonnet45ToSonnet46(): void {
-  if (getAPIProvider() !== 'firstParty') {
+  if (getAPIProvider() !== 'firstParty' || !isFirstPartyAnthropicBaseUrl()) {
     return
   }
 
diff --git a/src/migrations/resetProToOpusDefault.ts b/src/migrations/resetProToOpusDefault.ts
index 601872f7b..d7730d571 100644
--- a/src/migrations/resetProToOpusDefault.ts
+++ b/src/migrations/resetProToOpusDefault.ts
@@ -1,7 +1,10 @@
 import { logEvent } from 'src/services/analytics/index.js'
 import { isProSubscriber } from '../utils/auth.js'
 import { getGlobalConfig, saveGlobalConfig } from '../utils/config.js'
-import { getAPIProvider } from '../utils/model/providers.js'
+import {
+  getAPIProvider,
+  isFirstPartyAnthropicBaseUrl,
+} from '../utils/model/providers.js'
 import { getSettings_DEPRECATED } from '../utils/settings/settings.js'
 
 export function resetProToOpusDefault(): void {
@@ -23,6 +26,15 @@ export function resetProToOpusDefault(): void {
     return
   }
 
+  if (!isFirstPartyAnthropicBaseUrl()) {
+    saveGlobalConfig(current => ({
+      ...current,
+      opusProMigrationComplete: true,
+    }))
+    logEvent('tengu_reset_pro_to_opus_default', { skipped: true })
+    return
+  }
+
   const settings = getSettings_DEPRECATED()
 
   // Only show notification if user was on default (no custom model setting)
diff --git a/src/services/api/authRouting.ts b/src/services/api/authRouting.ts
index 7467f9227..f4ca52c8c 100644
--- a/src/services/api/authRouting.ts
+++ b/src/services/api/authRouting.ts
@@ -27,3 +27,22 @@ export function shouldUseFirstPartyAnthropicAuth(
     isFirstPartyBaseUrl: isFirstPartyAnthropicBaseUrl(),
   })
 }
+
+export function shouldUseCustomAnthropicBearerAuth({
+  providerOverride,
+  apiProvider,
+  isFirstPartyBaseUrl,
+  authToken,
+}: {
+  providerOverride?: ProviderOverride
+  apiProvider: APIProvider
+  isFirstPartyBaseUrl: boolean
+  authToken?: string
+}): boolean {
+  return Boolean(
+    !providerOverride &&
+      authToken?.trim() &&
+      apiProvider === 'firstParty' &&
+      !isFirstPartyBaseUrl,
+  )
+}
diff --git a/src/services/api/bootstrap.ts b/src/services/api/bootstrap.ts
index b91aed827..d6c1ddbe0 100644
--- a/src/services/api/bootstrap.ts
+++ b/src/services/api/bootstrap.ts
@@ -28,7 +28,10 @@ import { logForDebugging } from '../../utils/debug.js'
 import { withOAuth401Retry } from '../../utils/http.js'
 import { lazySchema } from '../../utils/lazySchema.js'
 import { logError } from '../../utils/log.js'
-import { getAPIProvider } from '../../utils/model/providers.js'
+import {
+  getAPIProvider,
+  isFirstPartyAnthropicBaseUrl,
+} from '../../utils/model/providers.js'
 import { isEssentialTrafficOnly } from '../../utils/privacyLevel.js'
 import type { ModelOption } from '../../utils/model/modelOptions.js'
 import {
@@ -133,7 +136,7 @@ async function fetchBootstrapAPI(): Promise<BootstrapResponse | null> {
     return null
   }
 
-  if (getAPIProvider() !== 'firstParty') {
+  if (getAPIProvider() !== 'firstParty' || !isFirstPartyAnthropicBaseUrl()) {
     logForDebugging('[Bootstrap] Skipped: 3P provider')
     return null
   }
diff --git a/src/services/api/claude.ts b/src/services/api/claude.ts
index f235b827c..789b48dc0 100644
--- a/src/services/api/claude.ts
+++ b/src/services/api/claude.ts
@@ -352,7 +352,12 @@ export function getPromptCachingEnabled(model: string): boolean {
   // format, so cache_control blocks are supported.
   const provider = getAPIProvider()
   const isNativeGithub = isGithubNativeAnthropicMode(model)
-  if (provider !== 'firstParty' && provider !== 'bedrock' && provider !== 'vertex' && !isNativeGithub) {
+  if (
+    (provider !== 'firstParty' || !isFirstPartyAnthropicBaseUrl()) &&
+    provider !== 'bedrock' &&
+    provider !== 'vertex' &&
+    !isNativeGithub
+  ) {
     return false
   }
 
@@ -1113,6 +1118,7 @@ async function* queryModel(
   // init (~10ms). For non-Opus models (haiku, sonnet) this skips the await
   // entirely. Subscribers don't hit this path at all.
   if (
+    isFirstPartyAnthropicBaseUrl() &&
     !isClaudeAISubscriber() &&
     isNonCustomOpusModel(options.model) &&
     (
@@ -1544,6 +1550,7 @@ async function* queryModel(
       !cacheEditingHeaderLatched &&
       cachedMCEnabled &&
       getAPIProvider() === 'firstParty' &&
+      isFirstPartyAnthropicBaseUrl() &&
       options.querySource === 'repl_main_thread'
     ) {
       cacheEditingHeaderLatched = true
@@ -1783,10 +1790,12 @@ async function* queryModel(
     const useCachedMC =
       cachedMCEnabled &&
       getAPIProvider() === 'firstParty' &&
+      isFirstPartyAnthropicBaseUrl() &&
       options.querySource === 'repl_main_thread'
     if (
       cacheEditingHeaderLatched &&
       getAPIProvider() === 'firstParty' &&
+      isFirstPartyAnthropicBaseUrl() &&
       options.querySource === 'repl_main_thread' &&
       !betasParams.includes(cacheEditingBetaHeader)
     ) {
diff --git a/src/services/api/client.oauthRouting.test.ts b/src/services/api/client.oauthRouting.test.ts
index 890ebaa09..f887cf8a4 100644
--- a/src/services/api/client.oauthRouting.test.ts
+++ b/src/services/api/client.oauthRouting.test.ts
@@ -1,5 +1,8 @@
 import { expect, test } from 'bun:test'
-import { shouldUseFirstPartyAnthropicAuthForProvider } from './authRouting.js'
+import {
+  shouldUseCustomAnthropicBearerAuth,
+  shouldUseFirstPartyAnthropicAuthForProvider,
+} from './authRouting.js'
 
 const providerOverride = {
   model: 'gpt-4o',
@@ -43,3 +46,34 @@ test('custom Anthropic base URLs do not use first-party Anthropic auth', () => {
     }),
   ).toBe(false)
 })
+
+test('custom Anthropic bearer tokens use native custom authentication', () => {
+  expect(
+    shouldUseCustomAnthropicBearerAuth({
+      apiProvider: 'firstParty',
+      isFirstPartyBaseUrl: false,
+      authToken: 'custom-token',
+    }),
+  ).toBe(true)
+})
+
+test('providerOverride routing does not use custom Anthropic bearer auth', () => {
+  expect(
+    shouldUseCustomAnthropicBearerAuth({
+      providerOverride,
+      apiProvider: 'firstParty',
+      isFirstPartyBaseUrl: false,
+      authToken: 'custom-token',
+    }),
+  ).toBe(false)
+})
+
+test('custom Anthropic bearer tokens are never forwarded to shim routes', () => {
+  expect(
+    shouldUseCustomAnthropicBearerAuth({
+      apiProvider: 'gemini',
+      isFirstPartyBaseUrl: false,
+      authToken: 'custom-token',
+    }),
+  ).toBe(false)
+})
diff --git a/src/services/api/client.test.ts b/src/services/api/client.test.ts
index 54273b6ee..9f5a77610 100644
--- a/src/services/api/client.test.ts
+++ b/src/services/api/client.test.ts
@@ -1,4 +1,4 @@
-import { afterEach, beforeEach, expect, test } from 'bun:test'
+import { afterEach, beforeEach, expect, mock, test } from 'bun:test'
 import { acquireSharedMutationLock, releaseSharedMutationLock } from '../../test/sharedMutationLock.js'
 import {
   _clearRegistryForTesting,
@@ -6,7 +6,25 @@ import {
   registerGateway,
 } from '../../integrations/index.js'
 import { publicBuildVersion } from '../../utils/version.js'
-import { getAnthropicClient } from './client.js'
+
+// bun:test keeps mock.module() registrations process-global across test files.
+// Load and re-register the real module before importing the client so a prior
+// provider mock cannot make this suite validate the wrong route in CI.
+const _realProvidersModule = await import(
+  `../../utils/model/providers.js?real=${Date.now()}-${Math.random()}`,
+)
+const realProviders = {
+  getAPIProvider: _realProvidersModule.getAPIProvider,
+  usesAnthropicAccountFlow: _realProvidersModule.usesAnthropicAccountFlow,
+  isGithubNativeAnthropicMode: _realProvidersModule.isGithubNativeAnthropicMode,
+  getAPIProviderForStatsig: _realProvidersModule.getAPIProviderForStatsig,
+  isFirstPartyAnthropicBaseUrl: _realProvidersModule.isFirstPartyAnthropicBaseUrl,
+}
+mock.module('../../utils/model/providers.js', () => realProviders)
+mock.module('src/utils/model/providers.js', () => realProviders)
+const { getAnthropicClient } = await import(
+  `./client.js?real=${Date.now()}-${Math.random()}`,
+)
 
 type FetchType = typeof globalThis.fetch
 
@@ -55,6 +73,8 @@ const originalEnv = {
   ANTHROPIC_BASE_URL: process.env.ANTHROPIC_BASE_URL,
   ANTHROPIC_MODEL: process.env.ANTHROPIC_MODEL,
   ANTHROPIC_CUSTOM_HEADERS: process.env.ANTHROPIC_CUSTOM_HEADERS,
+  USER_TYPE: process.env.USER_TYPE,
+  USE_STAGING_OAUTH: process.env.USE_STAGING_OAUTH,
   CLAUDE_CODE_PROVIDER_PROFILE_ENV_APPLIED:
     process.env.CLAUDE_CODE_PROVIDER_PROFILE_ENV_APPLIED,
   CLAUDE_CODE_PROVIDER_PROFILE_ENV_APPLIED_ID:
@@ -100,11 +120,13 @@ function clearEnvForMiniMaxOnlyTest(): void {
   delete process.env.AIMLAPI_API_KEY
   delete process.env.NVIDIA_NIM
   delete process.env.NVIDIA_API_KEY
-  delete process.env.ANTHROPIC_API_KEY
+  process.env.ANTHROPIC_API_KEY = 'must-not-forward'
   delete process.env.ANTHROPIC_AUTH_TOKEN
   delete process.env.ANTHROPIC_BASE_URL
   delete process.env.ANTHROPIC_MODEL
   delete process.env.ANTHROPIC_CUSTOM_HEADERS
+  delete process.env.USER_TYPE
+  delete process.env.USE_STAGING_OAUTH
 }
 
 beforeEach(async () => {
@@ -140,7 +162,7 @@ beforeEach(async () => {
   delete process.env.OPENAI_AUTH_HEADER_VALUE
   delete process.env.NVIDIA_NIM
   delete process.env.NVIDIA_API_KEY
-  delete process.env.ANTHROPIC_API_KEY
+  process.env.ANTHROPIC_API_KEY = 'must-not-forward'
   delete process.env.ANTHROPIC_AUTH_TOKEN
   delete process.env.ANTHROPIC_BASE_URL
   delete process.env.ANTHROPIC_MODEL
@@ -189,6 +211,8 @@ afterEach(() => {
     restoreEnv('ANTHROPIC_BASE_URL', originalEnv.ANTHROPIC_BASE_URL)
     restoreEnv('ANTHROPIC_MODEL', originalEnv.ANTHROPIC_MODEL)
     restoreEnv('ANTHROPIC_CUSTOM_HEADERS', originalEnv.ANTHROPIC_CUSTOM_HEADERS)
+    restoreEnv('USER_TYPE', originalEnv.USER_TYPE)
+    restoreEnv('USE_STAGING_OAUTH', originalEnv.USE_STAGING_OAUTH)
     restoreEnv(
       'CLAUDE_CODE_PROVIDER_PROFILE_ENV_APPLIED',
       originalEnv.CLAUDE_CODE_PROVIDER_PROFILE_ENV_APPLIED,
@@ -226,7 +250,7 @@ test('first-party Anthropic requests execute the configured fetch wrapper withou
   delete process.env.XAI_API_KEY
   delete process.env.MIMO_API_KEY
   delete process.env.VENICE_API_KEY
-  delete process.env.ANTHROPIC_API_KEY
+  process.env.ANTHROPIC_API_KEY = 'must-not-forward'
   delete process.env.ANTHROPIC_AUTH_TOKEN
   delete process.env.ANTHROPIC_BASE_URL
   delete process.env.ANTHROPIC_MODEL
@@ -278,11 +302,150 @@ test('first-party Anthropic requests execute the configured fetch wrapper withou
   expect(capturedHeaders).toBeDefined()
 })
 
+test('routes a custom Anthropic endpoint with ANTHROPIC_AUTH_TOKEN without requiring an API key', async () => {
+  let capturedUrl: string | undefined
+  let capturedHeaders: Headers | undefined
+
+  delete process.env.CLAUDE_CODE_USE_OPENAI
+  delete process.env.CLAUDE_CODE_USE_BEDROCK
+  delete process.env.CLAUDE_CODE_USE_VERTEX
+  delete process.env.CLAUDE_CODE_USE_FOUNDRY
+  delete process.env.CLAUDE_CODE_USE_GEMINI
+  delete process.env.CLAUDE_CODE_USE_GITHUB
+  delete process.env.CLAUDE_CODE_USE_MISTRAL
+  process.env.ANTHROPIC_API_KEY = 'must-not-forward'
+  process.env.ANTHROPIC_AUTH_TOKEN = 'custom-anthropic-token'
+  process.env.ANTHROPIC_BASE_URL = 'https://anthropic.example/api/v1'
+  process.env.USER_TYPE = 'ant'
+  process.env.USE_STAGING_OAUTH = '1'
+  process.env.ANTHROPIC_CUSTOM_HEADERS = 'X-Tenant: tenant-a\nauthorization: stale-value'
+
+  const fetchOverride = (async (input, init) => {
+    capturedUrl =
+      typeof input === 'string'
+        ? input
+        : input instanceof URL
+          ? input.toString()
+          : input.url
+    capturedHeaders = new Headers(init?.headers)
+    return new Response(
+      JSON.stringify({
+        id: 'msg_custom_anthropic',
+        type: 'message',
+        role: 'assistant',
+        model: 'claude-sonnet-4-6',
+        content: [{ type: 'text', text: 'ok' }],
+        stop_reason: 'end_turn',
+        stop_sequence: null,
+        container: null,
+        usage: { input_tokens: 1, output_tokens: 1 },
+      }),
+      { headers: { 'Content-Type': 'application/json' } },
+    )
+  }) as FetchType
+
+  const client = await getAnthropicClient({
+    maxRetries: 0,
+    model: 'claude-sonnet-4-6',
+    fetchOverride,
+  })
+
+  await client.messages.create({
+    model: 'claude-sonnet-4-6',
+    messages: [{ role: 'user', content: 'hello' }],
+    max_tokens: 64,
+  })
+
+  expect(capturedUrl).toBe('https://anthropic.example/api/v1/messages')
+  expect(capturedHeaders?.get('authorization')).toBe('Bearer custom-anthropic-token')
+  expect(capturedHeaders?.get('x-api-key')).toBeNull()
+  expect(capturedHeaders?.get('x-tenant')).toBe('tenant-a')
+})
+
+test('does not forward a custom bearer token to the first-party Anthropic endpoint', async () => {
+  let capturedHeaders: Headers | undefined
+
+  delete process.env.CLAUDE_CODE_USE_GEMINI
+  delete process.env.GEMINI_API_KEY
+  delete process.env.GEMINI_MODEL
+  delete process.env.GEMINI_BASE_URL
+  delete process.env.GEMINI_AUTH_MODE
+  process.env.ANTHROPIC_AUTH_TOKEN = 'custom-anthropic-token'
+  process.env.ANTHROPIC_BASE_URL = 'https://api.anthropic.com'
+
+  const fetchOverride = (async (_input, init) => {
+    capturedHeaders = new Headers(init?.headers)
+    return new Response(
+      JSON.stringify({
+        id: 'msg_first_party_key', type: 'message', role: 'assistant',
+        model: 'claude-sonnet-4-6', content: [{ type: 'text', text: 'ok' }],
+        stop_reason: 'end_turn', stop_sequence: null, container: null,
+        usage: { input_tokens: 1, output_tokens: 1 },
+      }),
+      { headers: { 'Content-Type': 'application/json' } },
+    )
+  }) as FetchType
+
+  const client = await getAnthropicClient({
+    apiKey: 'first-party-api-key',
+    maxRetries: 0,
+    model: 'claude-sonnet-4-6',
+    fetchOverride,
+  })
+  await client.messages.create({
+    model: 'claude-sonnet-4-6', messages: [{ role: 'user', content: 'hello' }], max_tokens: 64,
+  })
+
+  expect(capturedHeaders?.get('authorization')).toBeNull()
+  expect(capturedHeaders?.get('x-api-key')).toBe('first-party-api-key')
+})
+
+test('routes a custom Anthropic endpoint with native x-api-key authentication', async () => {
+  let capturedHeaders: Headers | undefined
+
+  delete process.env.CLAUDE_CODE_USE_OPENAI
+  delete process.env.CLAUDE_CODE_USE_BEDROCK
+  delete process.env.CLAUDE_CODE_USE_VERTEX
+  delete process.env.CLAUDE_CODE_USE_FOUNDRY
+  delete process.env.CLAUDE_CODE_USE_GEMINI
+  delete process.env.CLAUDE_CODE_USE_GITHUB
+  delete process.env.CLAUDE_CODE_USE_MISTRAL
+  delete process.env.ANTHROPIC_AUTH_TOKEN
+  process.env.ANTHROPIC_API_KEY = 'custom-anthropic-api-key'
+  process.env.ANTHROPIC_BASE_URL = 'https://anthropic.example/api'
+  process.env.ANTHROPIC_CUSTOM_HEADERS =
+    'X-Tenant: tenant-a\nauthorization: stale-value\nx-api-key: stale-key'
+
+  const fetchOverride = (async (_input, init) => {
+    capturedHeaders = new Headers(init?.headers)
+    return new Response(
+      JSON.stringify({
+        id: 'msg_custom_anthropic_key', type: 'message', role: 'assistant',
+        model: 'claude-sonnet-4-6', content: [{ type: 'text', text: 'ok' }],
+        stop_reason: 'end_turn', stop_sequence: null, container: null,
+        usage: { input_tokens: 1, output_tokens: 1 },
+      }),
+      { headers: { 'Content-Type': 'application/json' } },
+    )
+  }) as FetchType
+
+  const client = await getAnthropicClient({ maxRetries: 0, model: 'claude-sonnet-4-6', fetchOverride })
+  await client.messages.create({
+    model: 'claude-sonnet-4-6', messages: [{ role: 'user', content: 'hello' }], max_tokens: 64,
+  })
+
+  expect(capturedHeaders?.get('x-api-key')).toBe('custom-anthropic-api-key')
+  expect(capturedHeaders?.get('authorization')).toBeNull()
+  expect(capturedHeaders?.get('x-tenant')).toBe('tenant-a')
+})
+
 test('routes Gemini provider requests through the OpenAI-compatible shim', async () => {
   let capturedUrl: string | undefined
   let capturedHeaders: Headers | undefined
   let capturedBody: Record<string, unknown> | undefined
 
+  process.env.ANTHROPIC_AUTH_TOKEN = 'must-not-reach-gemini'
+
   globalThis.fetch = (async (input, init) => {
     capturedUrl =
       typeof input === 'string'
diff --git a/src/services/api/client.ts b/src/services/api/client.ts
index 5bd6b55f6..6508e67e9 100644
--- a/src/services/api/client.ts
+++ b/src/services/api/client.ts
@@ -49,7 +49,8 @@ import {
 } from '../../integrations/routeMetadata.js'
 import { resolveOpenAIShimRuntimeContext } from '../../integrations/runtimeMetadata.js'
 import {
-  shouldUseFirstPartyAnthropicAuth,
+  shouldUseCustomAnthropicBearerAuth,
+  shouldUseFirstPartyAnthropicAuthForProvider,
   type ProviderOverride,
 } from './authRouting.js'
 import { AnthropicVertex } from './vertexClient.js'
@@ -465,8 +466,13 @@ export async function getAnthropicClient({
     applyAimlapiEnvOnlyDefaults()
   }
 
-  const shouldUseFirstPartyAuth =
-    shouldUseFirstPartyAnthropicAuth(providerOverride)
+  const apiProvider = getAPIProvider()
+  const isFirstPartyBaseUrl = isFirstPartyAnthropicBaseUrl()
+  const shouldUseFirstPartyAuth = shouldUseFirstPartyAnthropicAuthForProvider({
+    providerOverride,
+    apiProvider,
+    isFirstPartyBaseUrl,
+  })
   const useMiniMaxNativeProvider =
     useMiniMaxEnvOnlyProvider ||
     (getAPIProvider() === 'minimax' &&
@@ -480,9 +486,29 @@ export async function getAnthropicClient({
 
   const isClaudeAiSubscriber =
     shouldUseFirstPartyAuth && isClaudeAISubscriber()
+  const anthropicAuthToken = process.env.ANTHROPIC_AUTH_TOKEN?.trim()
+  const usesCustomAnthropicAuthToken = shouldUseCustomAnthropicBearerAuth({
+    providerOverride,
+    apiProvider,
+    isFirstPartyBaseUrl,
+    authToken: anthropicAuthToken,
+  })
 
-  if (shouldUseFirstPartyAuth && !isClaudeAiSubscriber) {
-    await configureApiKeyHeaders(defaultHeaders, getIsNonInteractiveSession())
+  if (
+    (shouldUseFirstPartyAuth && !isClaudeAiSubscriber) ||
+    usesCustomAnthropicAuthToken
+  ) {
+    await configureApiKeyHeaders(
+      defaultHeaders,
+      getIsNonInteractiveSession(),
+      usesCustomAnthropicAuthToken ? anthropicAuthToken : undefined,
+    )
+  } else if (apiProvider === 'firstParty' && !isFirstPartyBaseUrl) {
+    removeManagedAnthropicAuthHeaders(defaultHeaders)
+    const anthropicApiKey = process.env.ANTHROPIC_API_KEY?.trim()
+    if (anthropicApiKey) {
+      defaultHeaders['X-Api-Key'] = anthropicApiKey
+    }
   }
 
   const resolvedFetch = buildFetch(fetchOverride, source)
@@ -733,20 +759,28 @@ export async function getAnthropicClient({
 
   // Determine authentication method based on available tokens
   const clientConfig: ConstructorParameters<typeof Anthropic>[0] = {
-    apiKey: isClaudeAiSubscriber
+    apiKey: isClaudeAiSubscriber || usesCustomAnthropicAuthToken
       ? null
       : useMiniMaxNativeProvider
         ? process.env.MINIMAX_API_KEY || process.env.ANTHROPIC_API_KEY
-        : apiKey || getAnthropicApiKey(),
+        : apiKey ||
+          (!isFirstPartyBaseUrl
+            ? process.env.ANTHROPIC_API_KEY?.trim()
+            : getAnthropicApiKey()),
+    // Pass an explicit null for non-Bearer routes so the SDK cannot fall back
+    // to ANTHROPIC_AUTH_TOKEN from its own environment lookup.
     authToken: isClaudeAiSubscriber
       ? getClaudeAIOAuthTokens()?.accessToken
-      : undefined,
+      : usesCustomAnthropicAuthToken
+        ? anthropicAuthToken
+        : null,
     // Set baseURL from OAuth config when using staging OAuth
-    ...(process.env.USER_TYPE === 'ant' &&
+    ...(shouldUseFirstPartyAuth &&
+    process.env.USER_TYPE === 'ant' &&
     isEnvTruthy(process.env.USE_STAGING_OAUTH)
       ? { baseURL: getOauthConfig().BASE_API_URL }
       : process.env.ANTHROPIC_BASE_URL
-        ? { baseURL: process.env.ANTHROPIC_BASE_URL }
+        ? { baseURL: process.env.ANTHROPIC_BASE_URL.replace(/\/v1\/?$/i, '') }
         : {}),
     ...ARGS,
     ...(isDebugToStdErr() && { logger: createStderrLogger() }),
@@ -758,15 +792,29 @@ export async function getAnthropicClient({
 async function configureApiKeyHeaders(
   headers: Record<string, string>,
   isNonInteractiveSession: boolean,
+  authToken?: string,
 ): Promise<void> {
-  const token =
-    process.env.ANTHROPIC_AUTH_TOKEN ||
-    (await getApiKeyFromApiKeyHelper(isNonInteractiveSession))
+  const token = authToken || (await getApiKeyFromApiKeyHelper(isNonInteractiveSession))
   if (token) {
+    removeManagedAnthropicAuthHeaders(headers)
     headers['Authorization'] = `Bearer ${token}`
   }
 }
 
+function removeManagedAnthropicAuthHeaders(headers: Record<string, string>): void {
+  for (const name of Object.keys(headers)) {
+    const lower = name.toLowerCase()
+    if (lower === 'authorization' || lower === 'x-api-key' || lower === 'api-key') {
+      delete headers[name]
+    }
+  }
+  // The Anthropic SDK also reads ANTHROPIC_CUSTOM_HEADERS. Null sentinels clear
+  // those env-parsed managed auth headers before the supported credential wins.
+  headers.Authorization = null as unknown as string
+  headers['X-Api-Key'] = null as unknown as string
+  headers['api-key'] = null as unknown as string
+}
+
 function getCustomHeaders(): Record<string, string> {
   const customHeaders: Record<string, string> = {}
   const customHeadersEnv = process.env.ANTHROPIC_CUSTOM_HEADERS
@@ -784,7 +832,13 @@ function getCustomHeaders(): Record<string, string> {
     if (colonIdx === -1) continue
     const name = headerString.slice(0, colonIdx).trim()
     const value = headerString.slice(colonIdx + 1).trim()
-    if (name) {
+    const lowerName = name.toLowerCase()
+    if (
+      name &&
+      lowerName !== 'authorization' &&
+      lowerName !== 'x-api-key' &&
+      lowerName !== 'api-key'
+    ) {
       customHeaders[name] = value
     }
   }
diff --git a/src/services/api/errors.ts b/src/services/api/errors.ts
index 36a11d16d..b7c4527b5 100644
--- a/src/services/api/errors.ts
+++ b/src/services/api/errors.ts
@@ -30,7 +30,11 @@ import {
   isNonCustomOpusModel,
 } from 'src/utils/model/model.js'
 import { getModelStrings } from 'src/utils/model/modelStrings.js'
-import { getAPIProvider } from 'src/utils/model/providers.js'
+import {
+  getAPIProvider,
+  isFirstPartyAnthropicBaseUrl,
+  isFirstPartyAnthropicProvider,
+} from 'src/utils/model/providers.js'
 import { getIsNonInteractiveSession } from '../../bootstrap/state.js'
 import {
   API_PDF_MAX_PAGES,
@@ -373,7 +377,7 @@ export const CCR_AUTH_ERROR_MESSAGE =
   'Authentication error · This may be a temporary network issue, please try again'
 export const REPEATED_529_ERROR_MESSAGE = 'Repeated 529 Overloaded errors'
 export function getCustomOffSwitchMessage(): string {
-  return getAPIProvider() === 'firstParty'
+  return isFirstPartyAnthropicProvider()
     ? 'Opus is experiencing high load, please use /model to switch to Sonnet'
     : 'The API is experiencing high load, please try again shortly or use /model to switch models'
 }
@@ -1200,7 +1204,7 @@ export function getAssistantMessageFromError(
   if (
     error instanceof Error &&
     error.message.toLowerCase().includes('x-api-key') &&
-    getAPIProvider() === 'firstParty'
+    isFirstPartyAnthropicProvider()
   ) {
     // In CCR mode, auth is via JWTs - this is likely a transient network issue
     if (isCCRMode()) {
@@ -1266,7 +1270,9 @@ export function getAssistantMessageFromError(
       error: 'authentication_failed',
       content: getIsNonInteractiveSession()
         ? `Failed to authenticate. ${API_ERROR_MESSAGE_PREFIX}: Authentication failed (status ${error.status}). Check your API key configuration.`
-        : `Please run /login · ${API_ERROR_MESSAGE_PREFIX}: Authentication failed (status ${error.status}). Check your API key configuration.`,
+        : isFirstPartyAnthropicProvider()
+          ? `Please run /login · ${API_ERROR_MESSAGE_PREFIX}: Authentication failed (status ${error.status}). Check your API key configuration.`
+          : `${API_ERROR_MESSAGE_PREFIX}: Authentication failed (status ${error.status}). Check your provider credential configuration.`,
     })
   }
 
@@ -1351,7 +1357,7 @@ export function getAssistantMessageFromError(
  * Returns a model name suggestion, or undefined if no suggestion is applicable.
  */
 function get3PModelFallbackSuggestion(model: string): string | undefined {
-  if (getAPIProvider() === 'firstParty') {
+  if (isFirstPartyAnthropicProvider()) {
     return undefined
   }
   // @[MODEL LAUNCH]: Add a fallback suggestion chain for the new model → previous version for 3P
@@ -1618,7 +1624,7 @@ export function getErrorMessageIfRefusal(
   logEvent('tengu_refusal_api_response', {})
 
   const usagePolicyUrl =
-    getAPIProvider() === 'firstParty'
+    isFirstPartyAnthropicProvider()
       ? 'https://www.anthropic.com/legal/aup'
       : "your provider's acceptable use policy"
 
diff --git a/src/services/api/grove.ts b/src/services/api/grove.ts
index f8dad014d..d1ec76b69 100644
--- a/src/services/api/grove.ts
+++ b/src/services/api/grove.ts
@@ -18,6 +18,7 @@ import {
 } from '../../utils/http.js'
 import { logError } from '../../utils/log.js'
 import { getClaudeCodeUserAgent } from '../../utils/userAgent.js'
+import { isFirstPartyAnthropicProvider } from '../../utils/model/providers.js'
 
 // Cache expiration: 24 hours
 const GROVE_CACHE_EXPIRATION_MS = 24 * 60 * 60 * 1000
@@ -41,6 +42,13 @@ export type GroveConfig = {
  */
 export type ApiResult<T> = { success: true; data: T } | { success: false }
 
+function getGroveCacheKey(): string {
+  // Provider selection can change during a process lifetime. Keep first-party
+  // responses separate from the custom-provider no-op result so switching
+  // endpoints cannot surface stale account settings or disable Grove later.
+  return `${isFirstPartyAnthropicProvider()}:${process.env.ANTHROPIC_BASE_URL ?? ''}`
+}
+
 /**
  * Get the current Grove settings for the user account.
  * Returns ApiResult to distinguish between API failure and success.
@@ -51,6 +59,9 @@ export type ApiResult<T> = { success: true; data: T } | { success: false }
  */
 export const getGroveSettings = memoize(
   async (): Promise<ApiResult<AccountSettings>> => {
+    if (!isFirstPartyAnthropicProvider()) {
+      return { success: false }
+    }
     // Grove is a notification feature; during an outage, skipping it is correct.
     if (isEssentialTrafficOnly()) {
       return { success: false }
@@ -82,12 +93,14 @@ export const getGroveSettings = memoize(
       return { success: false }
     }
   },
+  getGroveCacheKey,
 )
 
 /**
  * Mark that the Grove notice has been viewed by the user
  */
 export async function markGroveNoticeViewed(): Promise<void> {
+  if (!isFirstPartyAnthropicProvider()) return
   try {
     await withOAuth401Retry(() => {
       const authHeaders = getAuthHeaders()
@@ -120,6 +133,7 @@ export async function markGroveNoticeViewed(): Promise<void> {
 export async function updateGroveSettings(
   groveEnabled: boolean,
 ): Promise<void> {
+  if (!isFirstPartyAnthropicProvider()) return
   try {
     await withOAuth401Retry(() => {
       const authHeaders = getAuthHeaders()
@@ -155,6 +169,9 @@ export async function updateGroveSettings(
  * false and the Grove dialog won't show until the next session.
  */
 export async function isQualifiedForGrove(): Promise<boolean> {
+  if (!isFirstPartyAnthropicProvider()) {
+    return false
+  }
   if (!isConsumerSubscriber()) {
     return false
   }
@@ -232,6 +249,9 @@ async function fetchAndStoreGroveConfig(accountId: string): Promise<void> {
  */
 export const getGroveNoticeConfig = memoize(
   async (): Promise<ApiResult<GroveConfig>> => {
+    if (!isFirstPartyAnthropicProvider()) {
+      return { success: false }
+    }
     // Grove is a notification feature; during an outage, skipping it is correct.
     if (isEssentialTrafficOnly()) {
       return { success: false }
@@ -276,6 +296,7 @@ export const getGroveNoticeConfig = memoize(
       return { success: false }
     }
   },
+  getGroveCacheKey,
 )
 
 /**
diff --git a/src/services/api/referral.ts b/src/services/api/referral.ts
index 13cdc9fdc..d6a7afcb7 100644
--- a/src/services/api/referral.ts
+++ b/src/services/api/referral.ts
@@ -9,6 +9,7 @@ import { getGlobalConfig, saveGlobalConfig } from '../../utils/config.js'
 import { logForDebugging } from '../../utils/debug.js'
 import { logError } from '../../utils/log.js'
 import { isEssentialTrafficOnly } from '../../utils/privacyLevel.js'
+import { isFirstPartyAnthropicProvider } from '../../utils/model/providers.js'
 import { getOAuthHeaders, prepareApiRequest } from '../../utils/teleport/api.js'
 import type {
   ReferralCampaign,
@@ -70,6 +71,7 @@ export async function fetchReferralRedemptions(
  */
 function shouldCheckForPasses(): boolean {
   return !!(
+    isFirstPartyAnthropicProvider() &&
     getOauthAccountInfo()?.organizationUuid &&
     isClaudeAISubscriber() &&
     getSubscriptionType() === 'max'
diff --git a/src/services/api/usage.ts b/src/services/api/usage.ts
index 6e2e106e2..8c6c29ef3 100644
--- a/src/services/api/usage.ts
+++ b/src/services/api/usage.ts
@@ -7,6 +7,7 @@ import {
 } from '../../utils/auth.js'
 import { getAuthHeaders } from '../../utils/http.js'
 import { getClaudeCodeUserAgent } from '../../utils/userAgent.js'
+import { isFirstPartyAnthropicProvider } from '../../utils/model/providers.js'
 import { isOAuthTokenExpired } from '../oauth/client.js'
 
 export type RateLimit = {
@@ -31,6 +32,9 @@ export type Utilization = {
 }
 
 export async function fetchUtilization(): Promise<Utilization | null> {
+  if (!isFirstPartyAnthropicProvider()) {
+    return {}
+  }
   if (!isClaudeAISubscriber() || !hasProfileScope()) {
     return {}
   }
diff --git a/src/services/claudeAiLimits.ts b/src/services/claudeAiLimits.ts
index 273f4536c..607dcddf5 100644
--- a/src/services/claudeAiLimits.ts
+++ b/src/services/claudeAiLimits.ts
@@ -7,7 +7,7 @@ import { getModelBetas } from '../utils/betas.js'
 import { getGlobalConfig, saveGlobalConfig } from '../utils/config.js'
 import { logError } from '../utils/log.js'
 import { getSmallFastModel } from '../utils/model/model.js'
-import { getAPIProvider } from '../utils/model/providers.js'
+import { getAPIProvider, isFirstPartyAnthropicBaseUrl } from '../utils/model/providers.js'
 import { isEssentialTrafficOnly } from '../utils/privacyLevel.js'
 import type { AnalyticsMetadata_I_VERIFIED_THIS_IS_NOT_CODE_OR_FILEPATHS } from './analytics/index.js'
 import { logEvent } from './analytics/index.js'
@@ -224,7 +224,7 @@ export async function checkQuotaStatus(): Promise<void> {
     return
   }
 
-  if (getAPIProvider() !== 'firstParty') {
+  if (getAPIProvider() !== 'firstParty' || !isFirstPartyAnthropicBaseUrl()) {
     return
   }
 
diff --git a/src/services/mcp/claudeai.ts b/src/services/mcp/claudeai.ts
index 36f70e243..353538c96 100644
--- a/src/services/mcp/claudeai.ts
+++ b/src/services/mcp/claudeai.ts
@@ -9,7 +9,10 @@ import { getClaudeAIOAuthTokens } from 'src/utils/auth.js'
 import { getGlobalConfig, saveGlobalConfig } from 'src/utils/config.js'
 import { logForDebugging } from 'src/utils/debug.js'
 import { isEnvDefinedFalsy } from 'src/utils/envUtils.js'
-import { getAPIProvider } from 'src/utils/model/providers.js'
+import {
+  getAPIProvider,
+  isFirstPartyAnthropicBaseUrl,
+} from 'src/utils/model/providers.js'
 import { clearMcpAuthCache } from './client.js'
 import { normalizeNameForMCP } from './normalization.js'
 import type { ScopedMcpServerConfig } from './types.js'
@@ -31,6 +34,13 @@ type ClaudeAIMcpServersResponse = {
 const FETCH_TIMEOUT_MS = 5000
 const MCP_SERVERS_BETA_HEADER = 'mcp-servers-2025-12-04'
 
+function getClaudeAIMcpConfigsCacheKey(): string {
+  // Provider selection can change during a process lifetime. Keep the
+  // first-party result separate from a custom-endpoint no-op so an in-process
+  // switch cannot expose stale organization MCP configuration.
+  return `${getAPIProvider()}:${process.env.ANTHROPIC_BASE_URL ?? ''}`
+}
+
 /**
  * Fetches MCP server configurations from Claude.ai org configs.
  * These servers are managed by the organization via Claude.ai.
@@ -48,6 +58,14 @@ export const fetchClaudeAIMcpConfigsIfEligible = memoize(
         })
         return {}
       }
+      if (!isFirstPartyAnthropicBaseUrl()) {
+        logForDebugging('[claudeai-mcp] Skipped: non-first-party base URL')
+        logEvent('tengu_claudeai_mcp_eligibility', {
+          state:
+            'non_first_party_base_url' as AnalyticsMetadata_I_VERIFIED_THIS_IS_NOT_CODE_OR_FILEPATHS,
+        })
+        return {}
+      }
 
       if (isEnvDefinedFalsy(process.env.ENABLE_CLAUDEAI_MCP_SERVERS)) {
         logForDebugging('[claudeai-mcp] Disabled via env var')
@@ -141,6 +159,7 @@ export const fetchClaudeAIMcpConfigsIfEligible = memoize(
       return {}
     }
   },
+  getClaudeAIMcpConfigsCacheKey,
 )
 
 /**
diff --git a/src/services/mcp/officialRegistry.ts b/src/services/mcp/officialRegistry.ts
index 114f72b96..1127fc9d5 100644
--- a/src/services/mcp/officialRegistry.ts
+++ b/src/services/mcp/officialRegistry.ts
@@ -1,7 +1,10 @@
 import axios from 'axios'
 import { logForDebugging } from '../../utils/debug.js'
 import { errorMessage } from '../../utils/errors.js'
-import { getAPIProvider } from '../../utils/model/providers.js'
+import {
+  getAPIProvider,
+  isFirstPartyAnthropicBaseUrl,
+} from '../../utils/model/providers.js'
 
 type RegistryServer = {
   server: {
@@ -37,7 +40,8 @@ export async function prefetchOfficialMcpUrls(): Promise<void> {
   }
 
   // The official first-party MCP registry is only relevant for first-party mode.
-  if (getAPIProvider() !== 'firstParty') {
+  if (getAPIProvider() !== 'firstParty' || !isFirstPartyAnthropicBaseUrl()) {
+    officialUrls = undefined
     return
   }
 
@@ -70,7 +74,11 @@ export async function prefetchOfficialMcpUrls(): Promise<void> {
  * URL is in the official MCP registry. Undefined registry → false (fail-closed).
  */
 export function isOfficialMcpUrl(normalizedUrl: string): boolean {
-  return officialUrls?.has(normalizedUrl) ?? false
+  return (
+    getAPIProvider() === 'firstParty' &&
+    isFirstPartyAnthropicBaseUrl() &&
+    (officialUrls?.has(normalizedUrl) ?? false)
+  )
 }
 
 export function resetOfficialMcpUrlsForTesting(): void {
diff --git a/src/tools/WebFetchTool/utils.ts b/src/tools/WebFetchTool/utils.ts
index b8562c56a..e9dc8bcce 100644
--- a/src/tools/WebFetchTool/utils.ts
+++ b/src/tools/WebFetchTool/utils.ts
@@ -8,7 +8,9 @@ import { queryHaiku } from '../../services/api/claude.js'
 import { AbortError } from '../../utils/errors.js'
 import { getWebFetchUserAgent } from '../../utils/http.js'
 import { logError } from '../../utils/log.js'
-import { getAPIProvider } from '../../utils/model/providers.js'
+import {
+  isFirstPartyAnthropicProvider,
+} from '../../utils/model/providers.js'
 import {
   isBinaryContentType,
   persistBinaryContent,
@@ -179,7 +181,7 @@ export async function checkDomainBlocklist(
   domain: string,
 ): Promise<DomainCheckResult> {
   // Third-party providers should not consult the first-party domain policy.
-  if (getAPIProvider() !== 'firstParty') {
+  if (!isFirstPartyAnthropicProvider()) {
     return { status: 'allowed' }
   }
 
diff --git a/src/tools/WebSearchTool/WebSearchTool.ts b/src/tools/WebSearchTool/WebSearchTool.ts
index 5ee37d3ac..a748e345f 100644
--- a/src/tools/WebSearchTool/WebSearchTool.ts
+++ b/src/tools/WebSearchTool/WebSearchTool.ts
@@ -3,7 +3,7 @@ import type {
   BetaWebSearchTool20250305,
 } from '@anthropic-ai/sdk/resources/beta/messages/messages.mjs'
 import { PRODUCT_DISPLAY_NAME } from 'src/constants/product.js'
-import { getAPIProvider } from 'src/utils/model/providers.js'
+import { getAPIProvider, isFirstPartyAnthropicBaseUrl } from 'src/utils/model/providers.js'
 import type { PermissionResult } from 'src/utils/permissions/PermissionResult.js'
 
 import { z } from 'zod/v4'
@@ -549,7 +549,7 @@ function shouldUseAdapterProvider(): boolean {
   // Auto mode: native/first-party/Codex take precedence over adapter
   if (isCodexResponsesWebSearchEnabled()) return false
   const provider = getAPIProvider()
-  if (provider === 'firstParty' || provider === 'vertex' || provider === 'foundry') {
+  if ((provider === 'firstParty' && isFirstPartyAnthropicBaseUrl()) || provider === 'vertex' || provider === 'foundry') {
     return false
   }
   // No native path available — fall back to adapter
@@ -566,7 +566,7 @@ function shouldUseAdapterProvider(): boolean {
 function hasNativeSearchFallback(): boolean {
   if (isCodexResponsesWebSearchEnabled()) return true
   const provider = getAPIProvider()
-  return provider === 'firstParty' || provider === 'vertex' || provider === 'foundry'
+  return (provider === 'firstParty' && isFirstPartyAnthropicBaseUrl()) || provider === 'vertex' || provider === 'foundry'
 }
 
 // ---------------------------------------------------------------------------
@@ -605,7 +605,7 @@ export const WebSearchTool = buildTool({
     const model = getMainLoopModel()
 
     // Enable for firstParty
-    if (provider === 'firstParty') {
+    if (provider === 'firstParty' && isFirstPartyAnthropicBaseUrl()) {
       return true
     }
 
diff --git a/src/tools/WebSearchTool/providers/brave.test.ts b/src/tools/WebSearchTool/providers/brave.test.ts
index 42f202e13..81c04d3aa 100644
--- a/src/tools/WebSearchTool/providers/brave.test.ts
+++ b/src/tools/WebSearchTool/providers/brave.test.ts
@@ -22,12 +22,9 @@ function stalledJsonResponse(status = 200): Response {
   })
 }
 
-function expectSignalAbort(signal: AbortSignal | undefined): Promise<void> {
-  expect(signal).toBeInstanceOf(AbortSignal)
-  if (signal?.aborted) return Promise.resolve()
-
-  return new Promise(resolve => {
-    signal?.addEventListener('abort', () => resolve(), { once: true })
+function pendingResponseUntilAbort(signal: AbortSignal | undefined): Promise<Response> {
+  return new Promise((_resolve, reject) => {
+    signal?.addEventListener('abort', () => reject(signal.reason), { once: true })
   })
 }
 
@@ -119,24 +116,15 @@ describe('braveProvider search', () => {
     await expect(braveProvider.search({ query: 'q' })).rejects.toThrow(/429/)
   })
 
-  test(
-    'rejects when the provider-level timeout elapses',
-    async () => {
-      process.env.WEB_SEARCH_TIMEOUT_SEC = '1'
+  test('rejects when the provider-level timeout elapses', async () => {
+    process.env.WEB_SEARCH_TIMEOUT_SEC = '1'
+    globalThis.fetch = ((_: any, init: any) =>
+      pendingResponseUntilAbort(init?.signal as AbortSignal | undefined)) as typeof fetch
 
-      let signalAborted: Promise<void> | undefined
-      globalThis.fetch = (async (_input: any, init: any) => {
-        signalAborted = expectSignalAbort(init?.signal as AbortSignal | undefined)
-        return new Promise<Response>(() => undefined)
-      }) as typeof fetch
-
-      await expect(braveProvider.search({ query: 'q' })).rejects.toThrow(
-        /Brave search timed out/,
-      )
-      await expect(signalAborted).resolves.toBeUndefined()
-    },
-    { timeout: 10_000 },
-  )
+    await expect(braveProvider.search({ query: 'q' })).rejects.toThrow(
+      /Brave search timed out/,
+    )
+  })
 
   test('rejects when the response body stalls after headers arrive', async () => {
     process.env.WEB_SEARCH_TIMEOUT_SEC = '1'
@@ -152,17 +140,11 @@ describe('braveProvider search', () => {
 
   test('rejects when a non-2xx error body stalls after headers arrive', async () => {
     process.env.WEB_SEARCH_TIMEOUT_SEC = '1'
-
-    let signalAborted: Promise<void> | undefined
-    globalThis.fetch = (async (_input: any, init: any) => {
-      signalAborted = expectSignalAbort(init?.signal as AbortSignal | undefined)
-      return stalledJsonResponse(500)
-    }) as typeof fetch
+    globalThis.fetch = (async (_input: any, _init: any) => stalledJsonResponse(500)) as typeof fetch
 
     await expect(braveProvider.search({ query: 'q' })).rejects.toThrow(
       /Brave search timed out/,
     )
-    await expect(signalAborted).resolves.toBeUndefined()
   })
 
   test('returns empty hits when web.results is missing', async () => {
diff --git a/src/utils/anthropicBaseUrl.test.ts b/src/utils/anthropicBaseUrl.test.ts
new file mode 100644
index 000000000..4ab268600
--- /dev/null
+++ b/src/utils/anthropicBaseUrl.test.ts
@@ -0,0 +1,57 @@
+import { describe, expect, test } from 'bun:test'
+import { isFirstPartyAnthropicBaseUrlForEnv } from './anthropicBaseUrl.js'
+
+describe('isFirstPartyAnthropicBaseUrlForEnv', () => {
+  test('accepts the canonical HTTPS endpoint with its explicit default port', () => {
+    expect(
+      isFirstPartyAnthropicBaseUrlForEnv({
+        ANTHROPIC_BASE_URL: 'https://api.anthropic.com:443',
+      }),
+    ).toBe(true)
+  })
+
+  test('rejects a non-default port on an Anthropic host', () => {
+    expect(
+      isFirstPartyAnthropicBaseUrlForEnv({
+        ANTHROPIC_BASE_URL: 'https://api.anthropic.com:444',
+      }),
+    ).toBe(false)
+  })
+
+  test('defaults to true when ANTHROPIC_BASE_URL is unset', () => {
+    expect(isFirstPartyAnthropicBaseUrlForEnv({})).toBe(true)
+  })
+
+  test('rejects non-HTTPS URLs and lookalike hosts', () => {
+    expect(
+      isFirstPartyAnthropicBaseUrlForEnv({
+        ANTHROPIC_BASE_URL: 'http://api.anthropic.com',
+      }),
+    ).toBe(false)
+    expect(
+      isFirstPartyAnthropicBaseUrlForEnv({
+        ANTHROPIC_BASE_URL: 'https://api.anthropic.com.evil.example',
+      }),
+    ).toBe(false)
+  })
+
+  test('only accepts the staging host for ant users', () => {
+    expect(
+      isFirstPartyAnthropicBaseUrlForEnv({
+        ANTHROPIC_BASE_URL: 'https://api-staging.anthropic.com',
+      }),
+    ).toBe(false)
+    expect(
+      isFirstPartyAnthropicBaseUrlForEnv({
+        ANTHROPIC_BASE_URL: 'https://api-staging.anthropic.com',
+        USER_TYPE: 'ant',
+      }),
+    ).toBe(true)
+  })
+
+  test('fails closed for malformed URLs', () => {
+    expect(
+      isFirstPartyAnthropicBaseUrlForEnv({ ANTHROPIC_BASE_URL: 'not a URL' }),
+    ).toBe(false)
+  })
+})
diff --git a/src/utils/anthropicBaseUrl.ts b/src/utils/anthropicBaseUrl.ts
new file mode 100644
index 000000000..2d3143474
--- /dev/null
+++ b/src/utils/anthropicBaseUrl.ts
@@ -0,0 +1,21 @@
+export function isFirstPartyAnthropicBaseUrlForEnv(
+  processEnv: NodeJS.ProcessEnv,
+): boolean {
+  const baseUrl = processEnv.ANTHROPIC_BASE_URL
+  if (!baseUrl) return true
+
+  try {
+    const allowedHosts = ['api.anthropic.com']
+    if (processEnv.USER_TYPE === 'ant') {
+      allowedHosts.push('api-staging.anthropic.com')
+    }
+    const url = new URL(baseUrl)
+    return (
+      url.protocol === 'https:' &&
+      allowedHosts.includes(url.hostname) &&
+      (url.port === '' || url.port === '443')
+    )
+  } catch {
+    return false
+  }
+}
diff --git a/src/utils/apiPreconnect.test.ts b/src/utils/apiPreconnect.test.ts
index 74a7f8258..0666f5a86 100644
--- a/src/utils/apiPreconnect.test.ts
+++ b/src/utils/apiPreconnect.test.ts
@@ -4,7 +4,6 @@ import {
   releaseSharedMutationLock,
 } from '../test/sharedMutationLock.js'
 import { asMockFetch } from '../test/typedMocks.js'
-import * as actualProviders from './model/providers.js'
 
 const originalEnv = { ...process.env }
 const originalFetch = globalThis.fetch
@@ -18,6 +17,9 @@ function getMockApiProvider() {
 
 async function importFreshModule() {
   mock.restore()
+  const actualProviders = await import(
+    `./model/providers.ts?actual=${Date.now()}-${Math.random()}`,
+  )
   mock.module('./model/providers.js', () => ({
     ...actualProviders,
     getAPIProvider: getMockApiProvider,
@@ -35,7 +37,6 @@ afterEach(() => {
     process.env = { ...originalEnv }
     globalThis.fetch = originalFetch
     mock.restore()
-    mock.module('./model/providers.js', () => actualProviders)
   } finally {
     releaseSharedMutationLock()
   }
@@ -103,10 +104,6 @@ describe('preconnectAnthropicApi', () => {
     delete process.env.CLAUDE_CODE_CLIENT_CERT
     delete process.env.CLAUDE_CODE_CLIENT_KEY
 
-    mock.module('./model/providers.js', () => ({
-      ...actualProviders,
-      getAPIProvider: () => 'firstParty',
-    }))
     const fetchMock = mock(() => Promise.resolve(new Response(null, { status: 200 })))
     globalThis.fetch = asMockFetch(fetchMock)
 
@@ -116,6 +113,17 @@ describe('preconnectAnthropicApi', () => {
     expect(fetchMock).toHaveBeenCalledTimes(1)
   })
 
+  test('does not preconnect to a custom Anthropic endpoint', async () => {
+    process.env.ANTHROPIC_BASE_URL = 'https://tenant.example'
+    const fetchMock = mock(() => Promise.resolve(new Response(null, { status: 200 })))
+    globalThis.fetch = asMockFetch(fetchMock)
+
+    const { preconnectAnthropicApi } = await importFreshModule()
+    preconnectAnthropicApi('firstParty')
+
+    expect(fetchMock).not.toHaveBeenCalled()
+  })
+
   test('keeps non-mocked provider exports available to neighboring imports', async () => {
     await importFreshModule()
 
diff --git a/src/utils/apiPreconnect.ts b/src/utils/apiPreconnect.ts
index 9b2df8054..abe80dbaa 100644
--- a/src/utils/apiPreconnect.ts
+++ b/src/utils/apiPreconnect.ts
@@ -26,7 +26,11 @@
 import { getOauthConfig } from '../constants/oauth.js'
 import { createCombinedAbortSignal } from './combinedAbortSignal.js'
 import { isEnvTruthy } from './envUtils.js'
-import { type APIProvider, getAPIProvider } from './model/providers.js'
+import {
+  type APIProvider,
+  getAPIProvider,
+  isFirstPartyAnthropicBaseUrl,
+} from './model/providers.js'
 
 let fired = false
 
@@ -37,7 +41,7 @@ export function preconnectAnthropicApi(
   fired = true
 
   // Third-party providers should not warm a connection to Anthropic.
-  if (apiProvider !== 'firstParty') {
+  if (apiProvider !== 'firstParty' || !isFirstPartyAnthropicBaseUrl()) {
     return
   }
 
diff --git a/src/utils/attachments.ts b/src/utils/attachments.ts
index d1ac1a70b..b1b4cffb0 100644
--- a/src/utils/attachments.ts
+++ b/src/utils/attachments.ts
@@ -65,7 +65,7 @@ import {
 } from 'src/types/textInputTypes.js'
 import { randomUUID, type UUID } from 'crypto'
 import { getSettings_DEPRECATED } from './settings/settings.js'
-import { getAPIProvider } from './model/providers.js'
+import { getAPIProvider, isFirstPartyAnthropicBaseUrl } from './model/providers.js'
 import { getEffortEnvOverride, modelSupportsXHighEffort } from './effort.js'
 import { getSnippetForTwoFileDiff } from 'src/tools/FileEditTool/utils.js'
 import type {
@@ -1540,6 +1540,7 @@ export function getUltracodePermissionAttachment(toolUseContext: ToolUseContext)
   if (
     !isUltracode ||
     getAPIProvider() !== 'firstParty' ||
+    !isFirstPartyAnthropicBaseUrl() ||
     // A per-agent providerOverride routes the actual request through a
     // third-party shim (runAgent.ts sets it; query.ts forwards it to
     // getAnthropicClient()), so the process-wide first-party check above is not
diff --git a/src/utils/auth.ts b/src/utils/auth.ts
index d55ebd3e6..ce8f51d76 100644
--- a/src/utils/auth.ts
+++ b/src/utils/auth.ts
@@ -10,7 +10,10 @@ import {
   logEvent,
 } from 'src/services/analytics/index.js'
 import { getModelStrings } from 'src/utils/model/modelStrings.js'
-import { getAPIProvider } from 'src/utils/model/providers.js'
+import {
+  getAPIProvider,
+  isFirstPartyAnthropicBaseUrl,
+} from 'src/utils/model/providers.js'
 import {
   getIsNonInteractiveSession,
   preferThirdPartyAuthentication,
@@ -1918,7 +1921,7 @@ export type UserAccountInfo = {
 export function getAccountInformation() {
   const apiProvider = getAPIProvider()
   // Only provide account info for first-party Anthropic API
-  if (apiProvider !== 'firstParty') {
+  if (apiProvider !== 'firstParty' || !isFirstPartyAnthropicBaseUrl()) {
     return undefined
   }
   const { source: authTokenSource } = getAuthTokenSource()
diff --git a/src/utils/betas.test.ts b/src/utils/betas.test.ts
index 9ce7e88c1..7f0f90d28 100644
--- a/src/utils/betas.test.ts
+++ b/src/utils/betas.test.ts
@@ -45,6 +45,7 @@ const PROVIDER_ENV_KEYS = [
   'FIREWORKS_API_KEY',
   'ANTHROPIC_BASE_URL',
   'ANTHROPIC_API_KEY',
+  'ANTHROPIC_AUTH_TOKEN',
   'ANTHROPIC_MODEL',
   'ANTHROPIC_BETAS',
   'OPENAI_BASE_URL',
@@ -208,6 +209,55 @@ test('isAnthropicProvider is true for firstParty', async () => {
   expect(isAnthropicProvider()).toBe(true)
 })
 
+test('custom Anthropic proxy endpoints do not receive first-party beta headers', async () => {
+  process.env.ANTHROPIC_BASE_URL = 'https://tenant.example'
+  process.env.ANTHROPIC_MODEL = 'tenant-model'
+  process.env.ANTHROPIC_AUTH_TOKEN = 'tenant-token'
+  process.env.ANTHROPIC_BETAS = 'tenant-beta-2026-01-01'
+
+  const {
+    getMergedBetas,
+    getModelBetas,
+    isAnthropicProvider,
+    modelSupportsAutoMode,
+    modelSupportsContextManagement,
+    modelSupportsISP,
+    modelSupportsStructuredOutputs,
+    shouldIncludeFirstPartyOnlyBetas,
+    shouldUseGlobalCacheScope,
+  } = await importFreshBetas()
+  expect(isAnthropicProvider()).toBe(false)
+  expect(getMergedBetas('tenant-model')).toEqual([])
+  expect(getModelBetas('claude-sonnet-4-6')).toEqual([])
+  expect(modelSupportsISP('claude-sonnet-4-5')).toBe(true)
+  expect(modelSupportsContextManagement('claude-sonnet-4-5')).toBe(true)
+  expect(modelSupportsStructuredOutputs('claude-sonnet-4-5')).toBe(false)
+  expect(modelSupportsAutoMode('claude-sonnet-4-5')).toBe(false)
+  expect(shouldIncludeFirstPartyOnlyBetas()).toBe(false)
+  expect(shouldUseGlobalCacheScope()).toBe(false)
+})
+
+test('switching from first-party Anthropic to a custom proxy clears beta headers', async () => {
+  const { getModelBetas } = await importFreshBetas()
+  expect(getModelBetas('claude-sonnet-4-6')).not.toEqual([])
+
+  process.env.ANTHROPIC_BASE_URL = 'https://tenant.example'
+  process.env.ANTHROPIC_MODEL = 'claude-sonnet-4-6'
+  process.env.ANTHROPIC_AUTH_TOKEN = 'tenant-token'
+  process.env.ANTHROPIC_BETAS = 'tenant-beta-2026-01-01'
+
+  expect(getModelBetas('claude-sonnet-4-6')).toEqual([])
+})
+
+test('first-party Anthropic retains the beta gates excluded for custom proxies', async () => {
+  const {
+    shouldIncludeFirstPartyOnlyBetas,
+    shouldUseGlobalCacheScope,
+  } = await importFreshBetas()
+  expect(shouldIncludeFirstPartyOnlyBetas()).toBe(true)
+  expect(shouldUseGlobalCacheScope()).toBe(true)
+})
+
 test('isAnthropicProvider is true for bedrock', async () => {
   process.env.CLAUDE_CODE_USE_BEDROCK = '1'
   const { isAnthropicProvider } = await importFreshBetas()
diff --git a/src/utils/betas.ts b/src/utils/betas.ts
index f5f9636a6..2360be3c2 100644
--- a/src/utils/betas.ts
+++ b/src/utils/betas.ts
@@ -27,7 +27,11 @@ import { has1mContext } from './context.js'
 import { isEnvDefinedFalsy, isEnvTruthy } from './envUtils.js'
 import { getCanonicalName } from './model/model.js'
 import { get3PModelCapabilityOverride } from './model/modelSupportOverrides.js'
-import { getAPIProvider, isGithubNativeAnthropicMode } from './model/providers.js'
+import {
+  getAPIProvider,
+  isFirstPartyAnthropicBaseUrl,
+  isGithubNativeAnthropicMode,
+} from './model/providers.js'
 import { getInitialSettings } from './settings/settings.js'
 
 /**
@@ -103,7 +107,7 @@ export function modelSupportsISP(model: string): boolean {
   if (provider === 'foundry') {
     return true
   }
-  if (provider === 'firstParty') {
+  if (provider === 'firstParty' && isFirstPartyAnthropicBaseUrl()) {
     return !canonical.includes('claude-3-')
   }
   return (
@@ -128,7 +132,7 @@ export function modelSupportsContextManagement(model: string): boolean {
   if (provider === 'foundry') {
     return true
   }
-  if (provider === 'firstParty') {
+  if (provider === 'firstParty' && isFirstPartyAnthropicBaseUrl()) {
     return !canonical.includes('claude-3-')
   }
   return (
@@ -143,7 +147,10 @@ export function modelSupportsStructuredOutputs(model: string): boolean {
   const canonical = getCanonicalName(model)
   const provider = getAPIProvider()
   // Structured outputs only supported on firstParty and Foundry (not Bedrock/Vertex yet)
-  if (provider !== 'firstParty' && provider !== 'foundry') {
+  if (
+    (provider !== 'firstParty' || !isFirstPartyAnthropicBaseUrl()) &&
+    provider !== 'foundry'
+  ) {
     return false
   }
   return (
@@ -165,7 +172,10 @@ export function modelSupportsAutoMode(model: string): boolean {
     // External: firstParty-only at launch (PI probes not wired for
     // Bedrock/Vertex/Foundry yet). Checked before allowModels so the GB
     // override can't enable auto mode on unsupported providers.
-    if (process.env.USER_TYPE !== 'ant' && getAPIProvider() !== 'firstParty') {
+    if (
+      getAPIProvider() !== 'firstParty' ||
+      !isFirstPartyAnthropicBaseUrl()
+    ) {
       return false
     }
     // GrowthBook override: tengu_auto_mode_config.allowModels force-enables
@@ -216,7 +226,8 @@ export function getToolSearchBetaHeader(): string {
  */
 export function shouldIncludeFirstPartyOnlyBetas(): boolean {
   return (
-    (getAPIProvider() === 'firstParty' || getAPIProvider() === 'foundry') &&
+    ((getAPIProvider() === 'firstParty' && isFirstPartyAnthropicBaseUrl()) ||
+      getAPIProvider() === 'foundry') &&
     !isEnvTruthy(process.env.CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS)
   )
 }
@@ -229,10 +240,21 @@ export function shouldIncludeFirstPartyOnlyBetas(): boolean {
 export function shouldUseGlobalCacheScope(): boolean {
   return (
     getAPIProvider() === 'firstParty' &&
+    isFirstPartyAnthropicBaseUrl() &&
     !isEnvTruthy(process.env.CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS)
   )
 }
 
+function getBetaCacheKey(model: string): string {
+  return [
+    model.toLowerCase(),
+    getAPIProvider(),
+    process.env.ANTHROPIC_BASE_URL ?? '',
+    process.env.USER_TYPE ?? '',
+    process.env.CLAUDE_CODE_USE_GITHUB ?? '',
+  ].join('\0')
+}
+
 export const getAllModelBetas = memoize((model: string): string[] => {
   const betaHeaders: string[] = []
   const isHaiku = getCanonicalName(model).includes('haiku')
@@ -368,21 +390,25 @@ export const getAllModelBetas = memoize((model: string): string[] => {
     )
   }
   return betaHeaders
-})
+}, getBetaCacheKey)
 
 export const getModelBetas = memoize((model: string): string[] => {
+  if (!shouldUseAnthropicBetaHeaders(model)) {
+    return []
+  }
   const modelBetas = getAllModelBetas(model)
   if (getAPIProvider() === 'bedrock') {
     return modelBetas.filter(b => !BEDROCK_EXTRA_PARAMS_HEADERS.has(b))
   }
   return modelBetas
-})
+}, getBetaCacheKey)
 
 export const getBedrockExtraBodyParamsBetas = memoize(
   (model: string): string[] => {
     const modelBetas = getAllModelBetas(model)
     return modelBetas.filter(b => BEDROCK_EXTRA_PARAMS_HEADERS.has(b))
   },
+  getBetaCacheKey,
 )
 
 /**
@@ -398,7 +424,12 @@ export const getBedrockExtraBodyParamsBetas = memoize(
  */
 export function isAnthropicProvider(): boolean {
   const provider = getAPIProvider()
-  return provider === 'firstParty' || provider === 'bedrock' || provider === 'vertex' || provider === 'foundry'
+  return (
+    (provider === 'firstParty' && isFirstPartyAnthropicBaseUrl()) ||
+    provider === 'bedrock' ||
+    provider === 'vertex' ||
+    provider === 'foundry'
+  )
 }
 
 export function getMergedBetas(
@@ -407,8 +438,9 @@ export function getMergedBetas(
 ): string[] {
   // Beta headers are Anthropic-specific. Non-Anthropic providers (OpenAI,
   // Gemini, Codex, etc.) do not understand them and may reject requests
-  // containing unknown headers. GitHub Native Anthropic mode is an exception.
-  if (!isAnthropicProvider() && !isGithubNativeAnthropicMode(model)) {
+  // containing unknown headers. Custom Anthropic proxies and GitHub Native
+  // Anthropic mode are exceptions because both use Anthropic wire format.
+  if (!shouldUseAnthropicBetaHeaders(model)) {
     return []
   }
 
@@ -441,6 +473,13 @@ export function getMergedBetas(
   return [...baseBetas, ...sdkBetas.filter(b => !baseBetas.includes(b))]
 }
 
+function shouldUseAnthropicBetaHeaders(model: string): boolean {
+  return (
+    isAnthropicProvider() ||
+    isGithubNativeAnthropicMode(model)
+  )
+}
+
 export function clearBetasCaches(): void {
   getAllModelBetas.cache?.clear?.()
   getModelBetas.cache?.clear?.()
diff --git a/src/utils/fastMode.ts b/src/utils/fastMode.ts
index 041b657ef..f79d9dbe2 100644
--- a/src/utils/fastMode.ts
+++ b/src/utils/fastMode.ts
@@ -26,7 +26,7 @@ import {
   type ModelSetting,
   parseUserSpecifiedModel,
 } from './model/model.js'
-import { getAPIProvider } from './model/providers.js'
+import { isFirstPartyAnthropicProvider } from './model/providers.js'
 import { isEssentialTrafficOnly } from './privacyLevel.js'
 import {
   getInitialSettings,
@@ -36,7 +36,7 @@ import {
 import { createSignal } from './signal.js'
 
 export function isFastModeEnabled(): boolean {
-  if (getAPIProvider() !== 'firstParty') {
+  if (!isFirstPartyAnthropicProvider()) {
     return false
   }
   return !isEnvTruthy(process.env.CLAUDE_CODE_DISABLE_FAST_MODE)
@@ -73,7 +73,7 @@ function getDisabledReasonMessage(
 }
 
 export function getFastModeUnavailableReason(): string | null {
-  if (getAPIProvider() !== 'firstParty') {
+  if (!isFirstPartyAnthropicProvider()) {
     return 'Fast mode is not available on third-party providers'
   }
 
diff --git a/src/utils/http.test.ts b/src/utils/http.test.ts
new file mode 100644
index 000000000..97bc12cad
--- /dev/null
+++ b/src/utils/http.test.ts
@@ -0,0 +1,49 @@
+import { afterEach, beforeEach, expect, test } from 'bun:test'
+
+import { getWebFetchUserAgent } from './http.js'
+
+const ROUTING_ENV_KEYS = [
+  'ANTHROPIC_BASE_URL',
+  'CLAUDE_CODE_USE_OPENAI',
+  'CLAUDE_CODE_USE_FOUNDRY',
+  'CLAUDE_CODE_USE_BEDROCK',
+  'CLAUDE_CODE_USE_VERTEX',
+  'CLAUDE_CODE_USE_GEMINI',
+  'CLAUDE_CODE_USE_GITHUB',
+  'CLAUDE_CODE_USE_MISTRAL',
+]
+
+const originalEnv = new Map(
+  ROUTING_ENV_KEYS.map(key => [key, process.env[key]]),
+)
+const originalMacro = (globalThis as Record<string, unknown>).MACRO
+
+beforeEach(() => {
+  ;(globalThis as Record<string, unknown>).MACRO = { VERSION: 'test-version' }
+})
+
+afterEach(() => {
+  for (const key of ROUTING_ENV_KEYS) {
+    const value = originalEnv.get(key)
+    if (value === undefined) {
+      delete process.env[key]
+    } else {
+      process.env[key] = value
+    }
+  }
+  ;(globalThis as Record<string, unknown>).MACRO = originalMacro
+})
+
+test('WebFetch identifies a custom Anthropic endpoint as third-party', () => {
+  process.env.ANTHROPIC_BASE_URL = 'https://proxy.example/v1'
+
+  expect(getWebFetchUserAgent()).toContain(
+    '+https://github.com/Gitlawb/openclaude',
+  )
+})
+
+test('WebFetch preserves the Anthropic support URL for first-party endpoints', () => {
+  process.env.ANTHROPIC_BASE_URL = 'https://api.anthropic.com'
+
+  expect(getWebFetchUserAgent()).toContain('+https://support.anthropic.com/')
+})
diff --git a/src/utils/http.ts b/src/utils/http.ts
index afbe10730..6536cb2b5 100644
--- a/src/utils/http.ts
+++ b/src/utils/http.ts
@@ -10,7 +10,7 @@ import {
   handleOAuth401Error,
   isClaudeAISubscriber,
 } from './auth.js'
-import { getAPIProvider } from './model/providers.js'
+import { isFirstPartyAnthropicProvider } from './model/providers.js'
 import { getClaudeCodeUserAgent } from './userAgent.js'
 import { getWorkload } from './workloadContext.js'
 
@@ -56,7 +56,7 @@ export function getMCPUserAgent(): string {
 // local CLI traffic from claude.ai server-side fetches.
 export function getWebFetchUserAgent(): string {
   const supportUrl =
-    getAPIProvider() === 'firstParty'
+    isFirstPartyAnthropicProvider()
       ? 'https://support.anthropic.com/'
       : 'https://github.com/Gitlawb/openclaude'
   return `Claude-User (${getClaudeCodeUserAgent()}; +${supportUrl})`
diff --git a/src/utils/model/model.openai-shim-providers.test.ts b/src/utils/model/model.openai-shim-providers.test.ts
index 67dc3bdef..3af48a4f2 100644
--- a/src/utils/model/model.openai-shim-providers.test.ts
+++ b/src/utils/model/model.openai-shim-providers.test.ts
@@ -16,26 +16,32 @@ import {
 } from '../settings/settingsCache.js'
 async function importFreshModelModule() {
   mock.restore()
+  const getAPIProvider = () => {
+    if (process.env.NVIDIA_NIM) return 'nvidia-nim'
+    if (process.env.MINIMAX_API_KEY) return 'minimax'
+    if (process.env.MIMO_API_KEY) return 'xiaomi-mimo'
+    if (process.env.CLAUDE_CODE_USE_GEMINI) return 'gemini'
+    if (process.env.CLAUDE_CODE_USE_MISTRAL) return 'mistral'
+    if (process.env.CLAUDE_CODE_USE_GITHUB) return 'github'
+    if (process.env.CLAUDE_CODE_USE_OPENAI) {
+      const baseUrl = process.env.OPENAI_BASE_URL ?? ''
+      const model = process.env.OPENAI_MODEL ?? ''
+      return baseUrl.includes('/backend-api/codex') || model.startsWith('codex')
+        ? 'codex'
+        : 'openai'
+    }
+    if (process.env.CLAUDE_CODE_USE_BEDROCK) return 'bedrock'
+    if (process.env.CLAUDE_CODE_USE_VERTEX) return 'vertex'
+    if (process.env.CLAUDE_CODE_USE_FOUNDRY) return 'foundry'
+    return 'firstParty'
+  }
   mock.module('./providers.js', () => ({
-    getAPIProvider: () => {
-      if (process.env.NVIDIA_NIM) return 'nvidia-nim'
-      if (process.env.MINIMAX_API_KEY) return 'minimax'
-      if (process.env.MIMO_API_KEY) return 'xiaomi-mimo'
-      if (process.env.CLAUDE_CODE_USE_GEMINI) return 'gemini'
-      if (process.env.CLAUDE_CODE_USE_MISTRAL) return 'mistral'
-      if (process.env.CLAUDE_CODE_USE_GITHUB) return 'github'
-      if (process.env.CLAUDE_CODE_USE_OPENAI) {
-        const baseUrl = process.env.OPENAI_BASE_URL ?? ''
-        const model = process.env.OPENAI_MODEL ?? ''
-        return baseUrl.includes('/backend-api/codex') || model.startsWith('codex')
-          ? 'codex'
-          : 'openai'
-      }
-      if (process.env.CLAUDE_CODE_USE_BEDROCK) return 'bedrock'
-      if (process.env.CLAUDE_CODE_USE_VERTEX) return 'vertex'
-      if (process.env.CLAUDE_CODE_USE_FOUNDRY) return 'foundry'
-      return 'firstParty'
-    },
+    getAPIProvider,
+    isFirstPartyAnthropicBaseUrl: () => !process.env.ANTHROPIC_BASE_URL,
+    isFirstPartyAnthropicProvider: () =>
+      getAPIProvider() === 'firstParty' && !process.env.ANTHROPIC_BASE_URL,
+    isCustomAnthropicProvider: () =>
+      getAPIProvider() === 'firstParty' && !!process.env.ANTHROPIC_BASE_URL,
   }))
   mock.module('./modelAllowlist.js', () => ({
     isModelAllowed: () => true,
@@ -67,6 +73,7 @@ const SAVED_ENV = {
   NVIDIA_NIM: process.env.NVIDIA_NIM,
   MINIMAX_API_KEY: process.env.MINIMAX_API_KEY,
   ANTHROPIC_MODEL: process.env.ANTHROPIC_MODEL,
+  ANTHROPIC_BASE_URL: process.env.ANTHROPIC_BASE_URL,
   MIMO_API_KEY: process.env.MIMO_API_KEY,
   OPENAI_MODEL: process.env.OPENAI_MODEL,
   OPENAI_BASE_URL: process.env.OPENAI_BASE_URL,
@@ -385,6 +392,34 @@ test('getDefaultHaikuModel returns OPENAI_MODEL for MiniMax', async () => {
   expect(getDefaultHaikuModel()).toBe('MiniMax-M2.5-highspeed')
 })
 
+test('getDefaultMainLoopModelSetting keeps the configured custom Anthropic model', async () => {
+  process.env.ANTHROPIC_BASE_URL = 'https://tenant.example'
+  process.env.ANTHROPIC_MODEL = 'tenant-model'
+
+  const { getDefaultMainLoopModelSetting } = await importFreshModelModule()
+  expect(getDefaultMainLoopModelSetting()).toBe('tenant-model')
+})
+
+test('modelDisplayString uses the configured custom Anthropic default', async () => {
+  process.env.ANTHROPIC_BASE_URL = 'https://tenant.example'
+  process.env.ANTHROPIC_MODEL = 'tenant-model'
+
+  const { modelDisplayString } = await importFreshModelModule()
+  expect(modelDisplayString(null)).toBe('Default (tenant-model)')
+})
+
+test('custom Anthropic endpoints retain their configured model and conservative defaults', async () => {
+  process.env.ANTHROPIC_BASE_URL = 'https://tenant.example'
+  process.env.ANTHROPIC_MODEL = 'tenant-model'
+
+  const { getDefaultOpusModel, getDefaultSonnetModel, getSmallFastModel } =
+    await importFreshModelModule()
+
+  expect(getSmallFastModel()).toBe('tenant-model')
+  expect(getDefaultOpusModel()).toBe('claude-opus-4-7')
+  expect(getDefaultSonnetModel()).toBe('claude-sonnet-4-5-20250929')
+})
+
 test('default helpers do not leak claude-* names to shim providers', async () => {
   // Umbrella guard: for each OpenAI-shim provider, none of the default-model
   // helpers may return an Anthropic-branded model name. That was the source
diff --git a/src/utils/model/model.ts b/src/utils/model/model.ts
index 0a63f9e1c..5577d0bbd 100644
--- a/src/utils/model/model.ts
+++ b/src/utils/model/model.ts
@@ -23,7 +23,12 @@ import { getModelStrings, resolveOverriddenModel } from './modelStrings.js'
 import { formatModelPricing, getOpus46CostTier } from '../modelCost.js'
 import { getSettings_DEPRECATED } from '../settings/settings.js'
 import type { PermissionMode } from '../permissions/PermissionMode.js'
-import { getAPIProvider } from './providers.js'
+import {
+  getAPIProvider,
+  isFirstPartyAnthropicBaseUrl,
+  isFirstPartyAnthropicProvider,
+  isCustomAnthropicProvider,
+} from './providers.js'
 import { LIGHTNING_BOLT } from '../../constants/figures.js'
 import { isModelAllowed } from './modelAllowlist.js'
 import { type ModelAlias, isModelAlias } from './aliases.js'
@@ -48,6 +53,9 @@ function normalizeModelSetting(value: unknown): ModelName | ModelAlias | undefin
 
 export function getSmallFastModel(): ModelName {
   if (process.env.ANTHROPIC_SMALL_FAST_MODEL) return process.env.ANTHROPIC_SMALL_FAST_MODEL
+  if (isCustomAnthropicProvider()) {
+    return process.env.ANTHROPIC_MODEL || getDefaultHaikuModel()
+  }
   // For Gemini provider, use a fast model
   if (getAPIProvider() === 'gemini') {
     return process.env.GEMINI_MODEL || 'gemini-2.0-flash-lite'
@@ -226,7 +234,7 @@ export function getDefaultOpusModel(): ModelName {
   // 3P providers (Bedrock, Vertex, Foundry) — kept as a separate branch
   // since 3P availability lags firstParty and these will diverge again at
   // the next model launch. Keep 3P on Opus 4.7 until they roll out 4.8.
-  if (getAPIProvider() !== 'firstParty') {
+  if (!isFirstPartyAnthropicProvider()) {
     return getModelStrings().opus47
   }
   return getModelStrings().opus48
@@ -274,7 +282,7 @@ export function getDefaultSonnetModel(): ModelName {
     return process.env.OPENAI_MODEL || 'grok-4.3'
   }
   // Default to Sonnet 4.5 for 3P since they may not have 4.6 yet
-  if (getAPIProvider() !== 'firstParty') {
+  if (!isFirstPartyAnthropicProvider()) {
     return getModelStrings().sonnet45
   }
   return getModelStrings().sonnet46
@@ -365,6 +373,12 @@ export function getRuntimeMainLoopModel(params: {
  * @returns The default model setting to use
  */
 export function getDefaultMainLoopModelSetting(): ModelName | ModelAlias {
+  // Custom Anthropic-compatible endpoints intentionally retain the legacy
+  // firstParty provider category, so prefer their explicitly configured model
+  // before the subscription and PAYG defaults below.
+  if (isCustomAnthropicProvider()) {
+    return process.env.ANTHROPIC_MODEL || getDefaultSonnetModel()
+  }
   // GitHub Copilot provider: check settings.model first, then env, then default
   if (getAPIProvider() === 'github') {
     const settings = getSettings_DEPRECATED() || {}
@@ -549,7 +563,7 @@ export function renderDefaultModelSetting(
 }
 
 export function getOpus46PricingSuffix(fastMode: boolean): string {
-  if (getAPIProvider() !== 'firstParty') return ''
+  if (!isFirstPartyAnthropicProvider()) return ''
   const pricing = formatModelPricing(getOpus46CostTier(fastMode))
   const fastModeIndicator = fastMode ? ` (${LIGHTNING_BOLT})` : ''
   return ` ·${fastModeIndicator} ${pricing}`
@@ -559,7 +573,7 @@ export function isOpus1mMergeEnabled(): boolean {
   if (
     is1mContextDisabled() ||
     isProSubscriber() ||
-    getAPIProvider() !== 'firstParty'
+    !isFirstPartyAnthropicProvider()
   ) {
     return false
   }
@@ -825,6 +839,7 @@ export function parseUserSpecifiedModel(
   // 3P providers may not yet have 4.6 capacity, so pass through unchanged.
   if (
     getAPIProvider() === 'firstParty' &&
+    isFirstPartyAnthropicBaseUrl() &&
     isLegacyOpusFirstParty(modelString) &&
     isLegacyModelRemapEnabled()
   ) {
@@ -909,7 +924,7 @@ export function isLegacyModelRemapEnabled(): boolean {
 
 export function modelDisplayString(model: ModelSetting): string {
   if (model === null) {
-    if (getAPIProvider() !== 'firstParty') {
+    if (!isFirstPartyAnthropicProvider()) {
       return `Default (${getDefaultMainLoopModel()})`
     }
     if (process.env.USER_TYPE === 'ant') {
diff --git a/src/utils/model/modelOptions.gateways.test.ts b/src/utils/model/modelOptions.gateways.test.ts
index c7ccca507..f0ba54cac 100644
--- a/src/utils/model/modelOptions.gateways.test.ts
+++ b/src/utils/model/modelOptions.gateways.test.ts
@@ -8,16 +8,25 @@ import {
   setSessionSettingsCache,
 } from '../settings/settingsCache.js'
 
-async function importFreshModelOptionsModule() {
+async function importFreshModelOptionsModule(
+  provider = 'openai',
+  isFirstPartyAnthropicBaseUrl = false,
+) {
   mock.restore()
   mock.module('./providers.js', () => ({
-    getAPIProvider: () => 'openai',
-    getAPIProviderForStatsig: () => 'openai',
-    isFirstPartyAnthropicBaseUrl: () => false,
+    getAPIProvider: () => provider,
+    getAPIProviderForStatsig: () => provider,
+    isFirstPartyAnthropicBaseUrl: () => isFirstPartyAnthropicBaseUrl,
+    isFirstPartyAnthropicProvider: () =>
+      provider === 'firstParty' && isFirstPartyAnthropicBaseUrl,
+    isCustomAnthropicProvider: () =>
+      provider === 'firstParty' && !isFirstPartyAnthropicBaseUrl,
     isGithubNativeAnthropicMode: () => false,
     usesAnthropicAccountFlow: () => false,
   }))
   const nonce = `${Date.now()}-${Math.random()}`
+  const modelModule = await import(`./model.js?modelOptionsTest=${nonce}`)
+  mock.module('./model.js', () => modelModule)
   return import(`./modelOptions.js?ts=${nonce}`)
 }
 
@@ -32,6 +41,9 @@ const originalEnv = {
   OPENAI_BASE_URL: process.env.OPENAI_BASE_URL,
   OPENAI_MODEL: process.env.OPENAI_MODEL,
   OPENAI_API_KEY: process.env.OPENAI_API_KEY,
+  ANTHROPIC_BASE_URL: process.env.ANTHROPIC_BASE_URL,
+  ANTHROPIC_MODEL: process.env.ANTHROPIC_MODEL,
+  ANTHROPIC_API_KEY: process.env.ANTHROPIC_API_KEY,
   OPENROUTER_API_KEY: process.env.OPENROUTER_API_KEY,
   ATLAS_CLOUD_API_KEY: process.env.ATLAS_CLOUD_API_KEY,
   CODEX_API_KEY: process.env.CODEX_API_KEY,
@@ -93,6 +105,18 @@ test('OpenRouter keeps static catalog entries and the active custom model', asyn
   expect(values).toContain('deepseek/deepseek-chat')
 })
 
+test('custom Anthropic endpoints use the third-party default description', async () => {
+  process.env.ANTHROPIC_BASE_URL = 'https://proxy.example/v1'
+  process.env.ANTHROPIC_MODEL = 'proxy-model'
+  process.env.ANTHROPIC_API_KEY = 'proxy-key'
+
+  const { getModelOptions } = await importFreshModelOptionsModule('firstParty')
+  const defaultOption = getModelOptions().find(option => option.value === null)
+
+  expect(defaultOption?.description).toContain('currently proxy-model')
+  expect(defaultOption?.description).not.toContain('$')
+})
+
 test('OpenRouter active profile cache merges with the static route catalog', async () => {
   process.env.CLAUDE_CODE_USE_OPENAI = '1'
   process.env.OPENAI_BASE_URL = 'https://openrouter.ai/api/v1'
@@ -143,4 +167,4 @@ test('Atlas Cloud canonicalizes static catalog aliases without hiding the catalo
   expect(values).not.toContain('claude-opus-4-8')
   expect(values).not.toContain('grok-code-fast-1')
   expect(values).not.toContain('grok-4')
-})
\ No newline at end of file
+})
diff --git a/src/utils/model/modelOptions.ts b/src/utils/model/modelOptions.ts
index e6fa1dacb..fa03053ad 100644
--- a/src/utils/model/modelOptions.ts
+++ b/src/utils/model/modelOptions.ts
@@ -1,7 +1,11 @@
 // biome-ignore-all assist/source/organizeImports: internal-only import markers must not be reordered
 import { getInitialMainLoopModel } from '../../bootstrap/state.js'
 import { getCatalogEntriesForRoute } from '../../integrations/index.js'
-import { resolveRouteIdFromBaseUrl } from '../../integrations/routeMetadata.js'
+import {
+  getTransportKindForRoute,
+  resolveActiveRouteIdFromEnv,
+  resolveRouteIdFromBaseUrl,
+} from '../../integrations/routeMetadata.js'
 import {
   getAdditionalModelOptionsCacheScope,
   resolveProviderRequest,
@@ -20,7 +24,12 @@ import {
 } from '../modelCost.js'
 import { getSettings_DEPRECATED } from '../settings/settings.js'
 import { checkOpus1mAccess, checkSonnet1mAccess } from './check1mAccess.js'
-import { getAPIProvider } from './providers.js'
+import {
+  getAPIProvider,
+  isCustomAnthropicProvider,
+  isFirstPartyAnthropicBaseUrl,
+  isFirstPartyAnthropicProvider,
+} from './providers.js'
 import { isModelAllowed } from './modelAllowlist.js'
 import {
   getCanonicalName,
@@ -141,12 +150,14 @@ function getScopedAdditionalModelOptions(): ModelOption[] {
 }
 
 export function getDefaultOptionForUser(fastMode = false): ModelOption {
-  const is3P = getAPIProvider() !== 'firstParty'
+  const is3P = !isFirstPartyAnthropicProvider()
+  const currentDefaultModel =
+    isCustomAnthropicProvider() && process.env.ANTHROPIC_MODEL
+      ? process.env.ANTHROPIC_MODEL
+      : getDefaultMainLoopModelSetting()
 
-  if (process.env.USER_TYPE === 'ant') {
-    const currentModel = renderDefaultModelSetting(
-      getDefaultMainLoopModelSetting(),
-    )
+  if (process.env.USER_TYPE === 'ant' && !is3P) {
+    const currentModel = renderDefaultModelSetting(currentDefaultModel)
     return {
       value: null,
       label: 'Default (recommended)',
@@ -159,7 +170,7 @@ export function getDefaultOptionForUser(fastMode = false): ModelOption {
     return {
       value: null,
       label: 'Default (recommended)',
-      description: `Use the default model (currently ${renderDefaultModelSetting(getDefaultMainLoopModelSetting())})`,
+      description: `Use the default model (currently ${renderDefaultModelSetting(currentDefaultModel)})`,
     }
   }
 
@@ -176,7 +187,7 @@ export function getDefaultOptionForUser(fastMode = false): ModelOption {
   return {
     value: null,
     label: 'Default (recommended)',
-    description: `Use the default model (currently ${renderDefaultModelSetting(getDefaultMainLoopModelSetting())})${is3P ? '' : ` · ${formatModelPricing(COST_TIER_3_15)}`}`,
+    description: `Use the default model (currently ${renderDefaultModelSetting(currentDefaultModel)})${is3P ? '' : ` · ${formatModelPricing(COST_TIER_3_15)}`}`,
   }
 }
 
@@ -572,6 +583,28 @@ function getModelOptionsBase(fastMode = false): ModelOption[] {
     return [defaultOption, ...inactiveProfileOptions]
   }
 
+  const activeProfile = getActiveProviderProfile()
+  const activeRouteId = resolveActiveRouteIdFromEnv(process.env, {
+    activeProfileProvider: activeProfile?.provider,
+    activeProfileBaseUrl: activeProfile?.baseUrl,
+  })
+  if (getTransportKindForRoute(activeRouteId ?? '') === 'anthropic-proxy') {
+    const directEnvOption =
+      profileModelOptions.length === 0 && process.env.ANTHROPIC_MODEL
+        ? [{
+            value: process.env.ANTHROPIC_MODEL,
+            label: process.env.ANTHROPIC_MODEL,
+            description: 'Custom Anthropic-compatible endpoint',
+          }]
+        : []
+    return [
+      getDefaultOptionForUser(fastMode),
+      ...profileModelOptions,
+      ...directEnvOption,
+      ...inactiveProfileOptions,
+    ]
+  }
+
   if (process.env.USER_TYPE === 'ant') {
     // Build options from antModels config
     const antModelOptions: ModelOption[] = getAntModels().map(m => ({
@@ -634,7 +667,6 @@ function getModelOptionsBase(fastMode = false): ModelOption[] {
   // other configured profile while a local/route profile is active (#1119).
   const activeRouteCatalogOptions = getActiveOpenAIRouteCatalogOptions()
   const openAIModelOptionsScope = getAdditionalModelOptionsCacheScope()
-  const activeProfile = getActiveProviderProfile()
   if (
     activeRouteCatalogOptions.length > 0 ||
     openAIModelOptionsScope?.startsWith('openai:')
@@ -659,7 +691,7 @@ function getModelOptionsBase(fastMode = false): ModelOption[] {
   }
 
   // PAYG 1P API: Default (Sonnet) + Sonnet 1M + Opus 4.8 + Opus 4.7 + Opus 4.6 + Opus 1M + Haiku
-  if (getAPIProvider() === 'firstParty') {
+  if (getAPIProvider() === 'firstParty' && isFirstPartyAnthropicBaseUrl()) {
     const payg1POptions = [getDefaultOptionForUser(fastMode)]
     if (checkSonnet1mAccess()) {
       payg1POptions.push(getSonnet46_1MOption())
@@ -1007,12 +1039,12 @@ export function getModelOptions(fastMode = false): ModelOption[] {
     return filterModelOptionsByAllowlist([...options, getCodexPlanOption()])
   } else if (customModel === 'gpt-5.3-codex-spark') {
     return filterModelOptionsByAllowlist([...options, getCodexSparkOption()])
-  } else if (customModel === 'opus' && getAPIProvider() === 'firstParty') {
+  } else if (customModel === 'opus' && getAPIProvider() === 'firstParty' && isFirstPartyAnthropicBaseUrl()) {
     return filterModelOptionsByAllowlist([
       ...options,
       getMaxOpusOption(fastMode),
     ])
-  } else if (customModel === 'opus[1m]' && getAPIProvider() === 'firstParty') {
+  } else if (customModel === 'opus[1m]' && getAPIProvider() === 'firstParty' && isFirstPartyAnthropicBaseUrl()) {
     return filterModelOptionsByAllowlist([
       ...options,
       getMergedOpus1MOption(fastMode),
diff --git a/src/utils/model/modelSupportOverrides.ts b/src/utils/model/modelSupportOverrides.ts
index a8d5050fc..164249327 100644
--- a/src/utils/model/modelSupportOverrides.ts
+++ b/src/utils/model/modelSupportOverrides.ts
@@ -1,5 +1,5 @@
 import memoize from 'lodash-es/memoize.js'
-import { getAPIProvider } from './providers.js'
+import { getAPIProvider, isFirstPartyAnthropicBaseUrl } from './providers.js'
 
 export type ModelCapabilityOverride =
   | 'effort'
@@ -37,6 +37,8 @@ function buildCapabilityOverrideCacheKey(
     model.toLowerCase(),
     capability,
     getAPIProvider(),
+    process.env.ANTHROPIC_BASE_URL ?? '',
+    process.env.USER_TYPE ?? '',
     ...envParts,
   ].join('\0')
 }
@@ -47,7 +49,10 @@ function buildCapabilityOverrideCacheKey(
  */
 export const get3PModelCapabilityOverride = memoize(
   (model: string, capability: ModelCapabilityOverride): boolean | undefined => {
-    if (getAPIProvider() === 'firstParty') {
+    if (
+      getAPIProvider() === 'firstParty' &&
+      isFirstPartyAnthropicBaseUrl()
+    ) {
       return undefined
     }
     const m = model.toLowerCase()
diff --git a/src/utils/model/providers.test.ts b/src/utils/model/providers.test.ts
index 9407e9478..c43fc5d96 100644
--- a/src/utils/model/providers.test.ts
+++ b/src/utils/model/providers.test.ts
@@ -16,6 +16,7 @@ const originalEnv = {
   MINIMAX_API_KEY: process.env.MINIMAX_API_KEY,
   ANTHROPIC_BASE_URL: process.env.ANTHROPIC_BASE_URL,
   ANTHROPIC_API_KEY: process.env.ANTHROPIC_API_KEY,
+  ANTHROPIC_AUTH_TOKEN: process.env.ANTHROPIC_AUTH_TOKEN,
   ANTHROPIC_MODEL: process.env.ANTHROPIC_MODEL,
   OPENAI_BASE_URL: process.env.OPENAI_BASE_URL,
   OPENAI_API_BASE: process.env.OPENAI_API_BASE,
@@ -63,6 +64,7 @@ function clearProviderEnv(): void {
   delete process.env.MINIMAX_API_KEY
   delete process.env.ANTHROPIC_BASE_URL
   delete process.env.ANTHROPIC_API_KEY
+  delete process.env.ANTHROPIC_AUTH_TOKEN
   delete process.env.ANTHROPIC_MODEL
   delete process.env.OPENAI_BASE_URL
   delete process.env.OPENAI_API_BASE
@@ -83,6 +85,26 @@ test('first-party provider keeps Anthropic account setup flow enabled', () => {
   )
 })
 
+test('custom Anthropic endpoints do not start the first-party account flow', async () => {
+  clearProviderEnv()
+  process.env.ANTHROPIC_BASE_URL = 'https://tenant.example'
+  process.env.ANTHROPIC_MODEL = 'tenant-model'
+  process.env.ANTHROPIC_AUTH_TOKEN = 'tenant-token'
+
+  const { usesAnthropicAccountFlow } = await importFreshProvidersModule()
+  expect(usesAnthropicAccountFlow()).toBe(false)
+})
+
+test('HTTP Anthropic URLs do not enable the first-party account flow', async () => {
+  clearProviderEnv()
+  process.env.ANTHROPIC_BASE_URL = 'http://api.anthropic.com'
+
+  const { isFirstPartyAnthropicBaseUrl, usesAnthropicAccountFlow } =
+    await importFreshProvidersModule()
+  expect(isFirstPartyAnthropicBaseUrl()).toBe(false)
+  expect(usesAnthropicAccountFlow()).toBe(false)
+})
+
 test.each([
   ['CLAUDE_CODE_USE_OPENAI', 'openai'],
   ['CLAUDE_CODE_USE_GITHUB', 'github'],
diff --git a/src/utils/model/providers.ts b/src/utils/model/providers.ts
index d56470729..f5d0d02b6 100644
--- a/src/utils/model/providers.ts
+++ b/src/utils/model/providers.ts
@@ -5,6 +5,7 @@ import {
   resolveActiveRouteIdFromEnv,
 } from '../../integrations/routeMetadata.js'
 import { isEnvTruthy } from '../envUtils.js'
+import { isFirstPartyAnthropicBaseUrlForEnv } from '../anthropicBaseUrl.js'
 
 // Legacy provider categories that older model/status/runtime callers still
 // consume. Descriptor route ids are the newer source of truth, but we keep
@@ -82,7 +83,15 @@ export function getAPIProvider(): LegacyAPIProvider {
 }
 
 export function usesAnthropicAccountFlow(): boolean {
-  return getAPIProvider() === 'firstParty'
+  return isFirstPartyAnthropicProvider()
+}
+
+export function isFirstPartyAnthropicProvider(): boolean {
+  return getAPIProvider() === 'firstParty' && isFirstPartyAnthropicBaseUrl()
+}
+
+export function isCustomAnthropicProvider(): boolean {
+  return getAPIProvider() === 'firstParty' && !isFirstPartyAnthropicBaseUrl()
 }
 
 /**
@@ -119,18 +128,5 @@ export function getAPIProviderForStatsig(): AnalyticsMetadata_I_VERIFIED_THIS_IS
  * (or api-staging.anthropic.com for ant users).
  */
 export function isFirstPartyAnthropicBaseUrl(): boolean {
-  const baseUrl = process.env.ANTHROPIC_BASE_URL
-  if (!baseUrl) {
-    return true
-  }
-  try {
-    const host = new URL(baseUrl).host
-    const allowedHosts = ['api.anthropic.com']
-    if (process.env.USER_TYPE === 'ant') {
-      allowedHosts.push('api-staging.anthropic.com')
-    }
-    return allowedHosts.includes(host)
-  } catch {
-    return false
-  }
+  return isFirstPartyAnthropicBaseUrlForEnv(process.env)
 }
diff --git a/src/utils/model/validateModel.ts b/src/utils/model/validateModel.ts
index 197d0f42b..155a2c7bb 100644
--- a/src/utils/model/validateModel.ts
+++ b/src/utils/model/validateModel.ts
@@ -1,7 +1,7 @@
 // biome-ignore-all assist/source/organizeImports: internal-only import markers must not be reordered
 import { MODEL_ALIASES } from './aliases.js'
 import { isModelAllowed } from './modelAllowlist.js'
-import { getAPIProvider } from './providers.js'
+import { getAPIProvider, isFirstPartyAnthropicProvider } from './providers.js'
 import { sideQuery } from '../sideQuery.js'
 import {
   NotFoundError,
@@ -218,7 +218,7 @@ function handleValidationError(
  * Suggest a fallback model for 3P users when the selected model is unavailable.
  */
 function get3PFallbackSuggestion(model: string): string | undefined {
-  if (getAPIProvider() === 'firstParty') {
+  if (isFirstPartyAnthropicProvider()) {
     return undefined
   }
   const lowerModel = model.toLowerCase()
diff --git a/src/utils/providerFlag.test.ts b/src/utils/providerFlag.test.ts
index bc44f4f46..767bed6a9 100644
--- a/src/utils/providerFlag.test.ts
+++ b/src/utils/providerFlag.test.ts
@@ -21,10 +21,15 @@ const ENV_KEYS = [
   'CLAUDE_CODE_USE_MISTRAL',
   'CLAUDE_CODE_USE_BEDROCK',
   'CLAUDE_CODE_USE_VERTEX',
+  'CLAUDE_CODE_USE_FOUNDRY',
   'OPENAI_BASE_URL',
   'OPENAI_API_BASE',
   'OPENAI_API_KEY',
   'OPENAI_MODEL',
+  'OPENAI_API_FORMAT',
+  'OPENAI_AUTH_HEADER',
+  'OPENAI_AUTH_SCHEME',
+  'OPENAI_AUTH_HEADER_VALUE',
   'GEMINI_MODEL',
   'NVIDIA_API_KEY',
   'NVIDIA_NIM',
@@ -39,6 +44,11 @@ const ENV_KEYS = [
   'CLOUDFLARE_API_TOKEN',
   'MISTRAL_MODEL',
   'ANTHROPIC_MODEL',
+  'ANTHROPIC_BASE_URL',
+  'ANTHROPIC_API_KEY',
+  'ANTHROPIC_AUTH_TOKEN',
+  'ANTHROPIC_CUSTOM_HEADERS',
+  'USER_TYPE',
 ]
 
 const originalEnv: Record<string, string | undefined> = {}
@@ -58,10 +68,15 @@ const RESET_KEYS = [
   'CLAUDE_CODE_USE_MISTRAL',
   'CLAUDE_CODE_USE_BEDROCK',
   'CLAUDE_CODE_USE_VERTEX',
+  'CLAUDE_CODE_USE_FOUNDRY',
   'OPENAI_BASE_URL',
   'OPENAI_API_BASE',
   'OPENAI_API_KEY',
   'OPENAI_MODEL',
+  'OPENAI_API_FORMAT',
+  'OPENAI_AUTH_HEADER',
+  'OPENAI_AUTH_SCHEME',
+  'OPENAI_AUTH_HEADER_VALUE',
   'GEMINI_MODEL',
   'NVIDIA_API_KEY',
   'NVIDIA_NIM',
@@ -76,6 +91,11 @@ const RESET_KEYS = [
   'CLOUDFLARE_API_TOKEN',
   'MISTRAL_MODEL',
   'ANTHROPIC_MODEL',
+  'ANTHROPIC_BASE_URL',
+  'ANTHROPIC_API_KEY',
+  'ANTHROPIC_AUTH_TOKEN',
+  'ANTHROPIC_CUSTOM_HEADERS',
+  'USER_TYPE',
 ] as const
 
 beforeEach(() => {
@@ -137,6 +157,102 @@ describe('applyProviderFlag - anthropic', () => {
     expect(process.env.CLAUDE_CODE_USE_OPENAI).toBeUndefined()
     expect(process.env.CLAUDE_CODE_USE_GEMINI).toBeUndefined()
   })
+
+  test('clears a previously selected custom Anthropic endpoint', () => {
+    process.env.ANTHROPIC_BASE_URL = 'https://proxy.example/v1'
+    process.env.ANTHROPIC_MODEL = 'proxy-model'
+    process.env.ANTHROPIC_API_KEY = 'proxy-api-key'
+    process.env.ANTHROPIC_AUTH_TOKEN = 'proxy-token'
+    process.env.ANTHROPIC_CUSTOM_HEADERS = 'x-tenant: example'
+
+    const result = applyProviderFlag('anthropic', [])
+
+    expect(result.error).toBeUndefined()
+    expect(process.env.ANTHROPIC_BASE_URL).toBeUndefined()
+    expect(process.env.ANTHROPIC_MODEL).toBeUndefined()
+    expect(process.env.ANTHROPIC_API_KEY).toBeUndefined()
+    expect(process.env.ANTHROPIC_AUTH_TOKEN).toBeUndefined()
+    expect(process.env.ANTHROPIC_CUSTOM_HEADERS).toBeUndefined()
+  })
+
+  test('preserves a first-party Anthropic API key', () => {
+    process.env.ANTHROPIC_API_KEY = 'first-party-key'
+
+    const result = applyProviderFlag('anthropic', [])
+
+    expect(result.error).toBeUndefined()
+    expect(process.env.ANTHROPIC_API_KEY).toBe('first-party-key')
+  })
+})
+
+describe('applyProviderFlag - custom Anthropic-compatible', () => {
+  test('requires a custom endpoint instead of sending its credential to Anthropic', () => {
+    process.env.ANTHROPIC_AUTH_TOKEN = 'proxy-token'
+
+    const result = applyProviderFlag('custom-anthropic', [])
+
+    expect(result.error).toContain('ANTHROPIC_BASE_URL')
+  })
+
+  test('rejects the first-party Anthropic endpoint instead of forwarding a custom credential', () => {
+    process.env.ANTHROPIC_BASE_URL = 'https://api.anthropic.com'
+    process.env.ANTHROPIC_AUTH_TOKEN = 'proxy-token'
+
+    const result = applyProviderFlag('custom-anthropic', [])
+
+    expect(result.error).toContain('non-Anthropic ANTHROPIC_BASE_URL')
+  })
+
+  test('rejects the internal first-party Anthropic staging endpoint', () => {
+    process.env.USER_TYPE = 'ant'
+    process.env.ANTHROPIC_BASE_URL = 'https://api-staging.anthropic.com'
+    process.env.ANTHROPIC_AUTH_TOKEN = 'proxy-token'
+
+    const result = applyProviderFlag('custom-anthropic', [])
+
+    expect(result.error).toContain('non-Anthropic ANTHROPIC_BASE_URL')
+  })
+
+  test('keeps native Anthropic routing and applies --model', () => {
+    process.env.ANTHROPIC_BASE_URL = 'https://proxy.example/v1'
+    process.env.ANTHROPIC_AUTH_TOKEN = 'proxy-token'
+    process.env.ANTHROPIC_API_KEY = 'stale-anthropic-key'
+    process.env.CLAUDE_CODE_USE_FOUNDRY = '1'
+    process.env.OPENAI_BASE_URL = 'https://stale.example/v1'
+    process.env.OPENAI_API_BASE = 'https://stale.example/v1'
+    process.env.OPENAI_API_FORMAT = 'responses'
+    process.env.OPENAI_AUTH_HEADER = 'Authorization'
+    process.env.OPENAI_AUTH_SCHEME = 'bearer'
+    process.env.OPENAI_AUTH_HEADER_VALUE = 'stale-token'
+
+    const result = applyProviderFlag('custom-anthropic', ['--model', 'proxy-model'])
+
+    expect(result.error).toBeUndefined()
+    expect(process.env.CLAUDE_CODE_USE_OPENAI).toBeUndefined()
+    expect(process.env.CLAUDE_CODE_USE_FOUNDRY).toBeUndefined()
+    expect(process.env.OPENAI_MODEL).toBeUndefined()
+    expect(process.env.OPENAI_BASE_URL).toBeUndefined()
+    expect(process.env.OPENAI_API_BASE).toBeUndefined()
+    expect(process.env.OPENAI_API_FORMAT).toBeUndefined()
+    expect(process.env.OPENAI_AUTH_HEADER).toBeUndefined()
+    expect(process.env.OPENAI_AUTH_SCHEME).toBeUndefined()
+    expect(process.env.OPENAI_AUTH_HEADER_VALUE).toBeUndefined()
+    expect(process.env.ANTHROPIC_BASE_URL).toBe('https://proxy.example/v1')
+    expect(process.env.ANTHROPIC_AUTH_TOKEN).toBe('proxy-token')
+    expect(process.env.ANTHROPIC_API_KEY).toBeUndefined()
+    expect(process.env.ANTHROPIC_MODEL).toBe('proxy-model')
+  })
+
+  test('accepts native x-api-key authentication', () => {
+    process.env.ANTHROPIC_BASE_URL = 'https://proxy.example/v1'
+    process.env.ANTHROPIC_API_KEY = 'stale-first-party-key'
+
+    const result = applyProviderFlag('custom-anthropic', [])
+
+    expect(result.error).toBeUndefined()
+    expect(process.env.ANTHROPIC_API_KEY).toBe('stale-first-party-key')
+    expect(process.env.ANTHROPIC_AUTH_TOKEN).toBeUndefined()
+  })
 })
 
 describe('VALID_PROVIDERS', () => {
@@ -149,6 +265,7 @@ describe('VALID_PROVIDERS', () => {
     expect(VALID_PROVIDERS).toContain('venice')
     expect(VALID_PROVIDERS).toContain('xiaomi-mimo')
     expect(VALID_PROVIDERS).toContain('xiaomi-mimo-token')
+    expect(VALID_PROVIDERS).toContain('custom-anthropic')
   })
 })
 
diff --git a/src/utils/providerFlag.ts b/src/utils/providerFlag.ts
index a7f770957..3a8d24ce0 100644
--- a/src/utils/providerFlag.ts
+++ b/src/utils/providerFlag.ts
@@ -15,6 +15,8 @@
 import '../integrations/index.js'
 import {
   ensureIntegrationsLoaded,
+  getAnthropicProxy,
+  getAllAnthropicProxies,
   getAllGateways,
   getAllVendors,
   getGateway,
@@ -24,6 +26,7 @@ import {
   resolveRouteIdFromBaseUrl,
 } from '../integrations/index.js'
 import { PRESET_VENDOR_MAP } from '../integrations/compatibility.js'
+import { isFirstPartyAnthropicBaseUrlForEnv } from './anthropicBaseUrl.js'
 
 const PREFERRED_PROVIDER_ORDER = [
   'anthropic',
@@ -53,6 +56,7 @@ function buildValidProviders(): string[] {
     ...PRESET_VENDOR_MAP.map(mapping => mapping.preset),
     ...getAllVendors().map(vendor => vendor.id),
     ...getAllGateways().map(gateway => gateway.id),
+    ...getAllAnthropicProxies().map(proxy => proxy.id),
   ])
 
   const preferred = PREFERRED_PROVIDER_ORDER.filter(provider =>
@@ -150,11 +154,12 @@ function getRouteDefaults(provider: string): {
   const gateway =
     (route.gatewayId ? getGateway(route.gatewayId) : undefined) ??
     getGateway(route.routeId)
+  const anthropicProxy = getAnthropicProxy(route.routeId)
 
-  const defaultModel = gateway?.defaultModel ?? vendor?.defaultModel
+  const defaultModel = gateway?.defaultModel ?? vendor?.defaultModel ?? anthropicProxy?.defaultModel
 
   return {
-    defaultBaseUrl: gateway?.defaultBaseUrl ?? vendor?.defaultBaseUrl,
+    defaultBaseUrl: gateway?.defaultBaseUrl ?? vendor?.defaultBaseUrl ?? anthropicProxy?.defaultBaseUrl,
     defaultModel,
   }
 }
@@ -330,6 +335,7 @@ export function applyProviderFlag(
   delete process.env.CLAUDE_CODE_USE_GITHUB
   delete process.env.CLAUDE_CODE_USE_BEDROCK
   delete process.env.CLAUDE_CODE_USE_VERTEX
+  delete process.env.CLAUDE_CODE_USE_FOUNDRY
   delete process.env.NVIDIA_NIM
   if (copiedOpenAIKeyProvider && provider !== copiedOpenAIKeyProvider) {
     delete process.env.OPENAI_API_KEY
@@ -339,8 +345,55 @@ export function applyProviderFlag(
   const { defaultBaseUrl, defaultModel } = getRouteDefaults(provider)
 
   switch (provider) {
-    case 'anthropic':
-      // Default — no env vars needed
+    case 'anthropic': {
+      // Default — clear any custom native proxy contract so this explicit
+      // provider flag cannot keep routing requests to a prior endpoint.
+      // Preserve a first-party API key: it is the normal credential for this
+      // provider and may have been supplied directly through the environment.
+      const hadCustomAnthropicEndpoint =
+        !isFirstPartyAnthropicBaseUrlForEnv(process.env)
+      delete process.env.ANTHROPIC_BASE_URL
+      delete process.env.ANTHROPIC_MODEL
+      if (hadCustomAnthropicEndpoint) {
+        delete process.env.ANTHROPIC_API_KEY
+      }
+      delete process.env.ANTHROPIC_AUTH_TOKEN
+      delete process.env.ANTHROPIC_CUSTOM_HEADERS
+      break
+    }
+
+    case 'custom-anthropic':
+      if (!process.env.ANTHROPIC_BASE_URL?.trim()) {
+        return {
+          error: 'Custom Anthropic-compatible provider requires ANTHROPIC_BASE_URL.',
+        }
+      }
+      if (isFirstPartyAnthropicBaseUrlForEnv(process.env)) {
+        return {
+          error: 'Custom Anthropic-compatible provider requires a non-Anthropic ANTHROPIC_BASE_URL.',
+        }
+      }
+      const hasAuthToken = Boolean(process.env.ANTHROPIC_AUTH_TOKEN?.trim())
+      const hasApiKey = Boolean(process.env.ANTHROPIC_API_KEY?.trim())
+      if (!hasAuthToken && !hasApiKey) {
+        return {
+          error: 'Custom Anthropic-compatible provider requires ANTHROPIC_AUTH_TOKEN or ANTHROPIC_API_KEY.',
+        }
+      }
+      if (hasAuthToken) {
+        delete process.env.ANTHROPIC_API_KEY
+      } else {
+        delete process.env.ANTHROPIC_AUTH_TOKEN
+      }
+      delete process.env.OPENAI_BASE_URL
+      delete process.env.OPENAI_API_BASE
+      delete process.env.OPENAI_MODEL
+      delete process.env.OPENAI_API_FORMAT
+      delete process.env.OPENAI_AUTH_HEADER
+      delete process.env.OPENAI_AUTH_SCHEME
+      delete process.env.OPENAI_AUTH_HEADER_VALUE
+      process.env.ANTHROPIC_MODEL ??= defaultModel
+      if (model) process.env.ANTHROPIC_MODEL = model
       break
 
     case 'openai':
diff --git a/src/utils/providerProfile.test.ts b/src/utils/providerProfile.test.ts
index bb9e277f2..bedb587a7 100644
--- a/src/utils/providerProfile.test.ts
+++ b/src/utils/providerProfile.test.ts
@@ -1,5 +1,5 @@
 import assert from 'node:assert/strict'
-import { existsSync, mkdtempSync, readFileSync, rmSync, statSync, writeFileSync } from 'node:fs'
+import { chmodSync, existsSync, mkdtempSync, readFileSync, rmSync, statSync, writeFileSync } from 'node:fs'
 import { tmpdir } from 'node:os'
 import { join } from 'node:path'
 import test, { afterEach, beforeEach } from 'node:test'
@@ -508,7 +508,7 @@ test('buildStartupEnvFromProfile preserves explicit OpenAI-compatible env withou
 })
 
 test('buildStartupEnvFromProfile preserves concrete env-only NIM setup over stale profile', async () => {
-  const processEnv = {
+  const processEnv: NodeJS.ProcessEnv = {
     OPENAI_BASE_URL: 'https://integrate.api.nvidia.com/v1',
     OPENAI_MODEL: 'qwen/qwen3.5-397b-a17b',
     NVIDIA_API_KEY: 'nvapi-live',
@@ -1111,6 +1111,29 @@ test('saveProfileFile writes a profile that loadProfileFile can read back', () =
   }
 })
 
+test('saveProfileFile restricts permissions when overwriting an existing profile', () => {
+  const cwd = mkdtempSync(join(tmpdir(), 'openclaude-profile-mode-'))
+
+  try {
+    const filePath = join(cwd, PROFILE_FILE_NAME)
+    writeFileSync(filePath, '{}', { encoding: 'utf8', mode: 0o644 })
+    chmodSync(filePath, 0o644)
+
+    saveProfileFile(
+      createProfileFile('anthropic', {
+        ANTHROPIC_AUTH_TOKEN: 'custom-bearer-token',
+      }),
+      { cwd },
+    )
+
+    if (process.platform !== 'win32') {
+      assert.equal(statSync(filePath).mode & 0o777, 0o600)
+    }
+  } finally {
+    rmSync(cwd, { recursive: true, force: true })
+  }
+})
+
 test('saveProfileFile defaults to user config instead of the working directory', async () => {
   const cwd = mkdtempSync(join(tmpdir(), 'openclaude-workspace-profile-'))
   const configRoot = mkdtempSync(join(tmpdir(), 'openclaude-config-profile-'))
@@ -1438,6 +1461,64 @@ test('buildStartupEnvFromProfile applies persisted gemini settings when no provi
   assert.equal(env.GEMINI_MODEL, 'gemini-2.5-flash')
 })
 
+test('buildStartupEnvFromProfile restores a persisted custom Anthropic Bearer token', async () => {
+  const env = await buildStartupEnvFromProfile({
+    persisted: profile('anthropic', {
+      ANTHROPIC_BASE_URL: 'https://anthropic-proxy.example/v1',
+      ANTHROPIC_MODEL: 'claude-proxy-model',
+      ANTHROPIC_AUTH_TOKEN: 'persisted-proxy-token',
+      ANTHROPIC_CUSTOM_HEADERS: 'X-Tenant: example',
+    }),
+    processEnv: {},
+  })
+
+  assert.equal(env.ANTHROPIC_BASE_URL, 'https://anthropic-proxy.example/v1')
+  assert.equal(env.ANTHROPIC_MODEL, 'claude-proxy-model')
+  assert.equal(env.ANTHROPIC_AUTH_TOKEN, 'persisted-proxy-token')
+  assert.equal(env.ANTHROPIC_API_KEY, undefined)
+  assert.equal(env.ANTHROPIC_CUSTOM_HEADERS, 'X-Tenant: example')
+})
+
+test('buildStartupEnvFromProfile does not leak a stray API key into a persisted custom Anthropic Bearer profile', async () => {
+  const env = await buildStartupEnvFromProfile({
+    persisted: profile('anthropic', {
+      ANTHROPIC_BASE_URL: 'https://anthropic-proxy.example/v1',
+      ANTHROPIC_MODEL: 'claude-proxy-model',
+      ANTHROPIC_AUTH_TOKEN: 'persisted-proxy-token',
+    }),
+    processEnv: { ANTHROPIC_API_KEY: 'sk-ant-stray-shell-key' },
+  })
+
+  assert.equal(env.ANTHROPIC_AUTH_TOKEN, 'persisted-proxy-token')
+  assert.equal(env.ANTHROPIC_API_KEY, undefined)
+})
+
+test('buildStartupEnvFromProfile preserves explicit custom Anthropic environment setup', async () => {
+  const processEnv: NodeJS.ProcessEnv = {
+    ANTHROPIC_BASE_URL: 'https://anthropic-proxy.example/v1',
+    ANTHROPIC_MODEL: 'claude-proxy-model',
+    ANTHROPIC_AUTH_TOKEN: 'env-proxy-token',
+  }
+  const env = await buildStartupEnvFromProfile({ persisted: null, processEnv })
+
+  assert.equal(env, processEnv)
+  assert.equal(env.CLAUDE_CODE_USE_OPENAI, undefined)
+  assert.equal(env.ANTHROPIC_AUTH_TOKEN, 'env-proxy-token')
+})
+
+test('buildStartupEnvFromProfile preserves custom Anthropic x-api-key setup', async () => {
+  const processEnv: NodeJS.ProcessEnv = {
+    ANTHROPIC_BASE_URL: 'https://anthropic-proxy.example/v1',
+    ANTHROPIC_MODEL: 'claude-proxy-model',
+    ANTHROPIC_API_KEY: 'env-proxy-key',
+  }
+  const env = await buildStartupEnvFromProfile({ persisted: null, processEnv })
+
+  assert.equal(env, processEnv)
+  assert.equal(env.CLAUDE_CODE_USE_OPENAI, undefined)
+  assert.equal(env.ANTHROPIC_API_KEY, 'env-proxy-key')
+})
+
 test('buildStartupEnvFromProfile rehydrates stored Gemini access token for access-token profile mode', async () => {
   const env = await buildStartupEnvFromProfile({
     persisted: profile('gemini', {
diff --git a/src/utils/providerProfile.ts b/src/utils/providerProfile.ts
index 5b6ad059b..4c9a31603 100644
--- a/src/utils/providerProfile.ts
+++ b/src/utils/providerProfile.ts
@@ -1,4 +1,4 @@
-import { existsSync, mkdirSync, readFileSync, rmSync, writeFileSync } from 'node:fs'
+import { chmodSync, existsSync, mkdirSync, readFileSync, rmSync, writeFileSync } from 'node:fs'
 import { dirname, join, resolve } from 'node:path'
 import {
   DEFAULT_CODEX_BASE_URL,
@@ -64,6 +64,7 @@ const PROFILE_ENV_KEYS = [
   'ANTHROPIC_BASE_URL',
   'ANTHROPIC_MODEL',
   'ANTHROPIC_API_KEY',
+  'ANTHROPIC_AUTH_TOKEN',
   'ANTHROPIC_CUSTOM_HEADERS',
   'ANTHROPIC_BEDROCK_BASE_URL',
   'ANTHROPIC_VERTEX_BASE_URL',
@@ -148,6 +149,7 @@ export type ProfileEnv = {
   ANTHROPIC_BASE_URL?: string
   ANTHROPIC_MODEL?: string
   ANTHROPIC_API_KEY?: string
+  ANTHROPIC_AUTH_TOKEN?: string
   ANTHROPIC_CUSTOM_HEADERS?: string
   ANTHROPIC_BEDROCK_BASE_URL?: string
   ANTHROPIC_VERTEX_BASE_URL?: string
@@ -1207,6 +1209,7 @@ export function saveProfileFile(
     encoding: 'utf8',
     mode: 0o600,
   })
+  chmodSync(filePath, 0o600)
   return filePath
 }
 
@@ -1318,6 +1321,21 @@ function hasConcreteProviderSelection(
     return true
   }
 
+  // Anthropic-native proxies are selected by their own endpoint, model, and
+  // Bearer token rather than a CLAUDE_CODE_USE_* flag. Treat that complete
+  // contract as explicit so fresh-install fallback cannot replace it with the
+  // default OpenAI-compatible provider.
+  if (
+    sanitizeProviderConfigValue(processEnv.ANTHROPIC_BASE_URL) !== undefined &&
+    normalizeProfileModel(
+      sanitizeProviderConfigValue(processEnv.ANTHROPIC_MODEL),
+    ) !== undefined &&
+    (sanitizeApiKey(processEnv.ANTHROPIC_AUTH_TOKEN) !== undefined ||
+      sanitizeApiKey(processEnv.ANTHROPIC_API_KEY) !== undefined)
+  ) {
+    return true
+  }
+
   // Env-only provider setups — no CLAUDE_CODE_USE_* flag needed
   return (
     sanitizeApiKey(processEnv.FIREWORKS_API_KEY) !== undefined ||
@@ -1492,9 +1510,13 @@ export async function buildLaunchEnv(options: {
     const anthropicBaseUrl =
       sanitizeProviderConfigValue(processEnv.ANTHROPIC_BASE_URL) ||
       sanitizeProviderConfigValue(persistedEnv.ANTHROPIC_BASE_URL)
-    const anthropicApiKey =
-      sanitizeApiKey(processEnv.ANTHROPIC_API_KEY) ||
-      sanitizeApiKey(persistedEnv.ANTHROPIC_API_KEY)
+    const anthropicAuthToken =
+      sanitizeApiKey(processEnv.ANTHROPIC_AUTH_TOKEN) ||
+      sanitizeApiKey(persistedEnv.ANTHROPIC_AUTH_TOKEN)
+    const anthropicApiKey = anthropicAuthToken
+      ? undefined
+      : sanitizeApiKey(processEnv.ANTHROPIC_API_KEY) ||
+        sanitizeApiKey(persistedEnv.ANTHROPIC_API_KEY)
 
     return buildCompatibilityProcessEnv({
       processEnv,
@@ -1514,6 +1536,15 @@ export async function buildLaunchEnv(options: {
         ...(anthropicApiKey
           ? { ANTHROPIC_API_KEY: anthropicApiKey }
           : {}),
+        ...(anthropicAuthToken
+          ? { ANTHROPIC_AUTH_TOKEN: anthropicAuthToken }
+          : {}),
+        ...(shellCustomHeaders || persistedCustomHeaders
+          ? {
+              ANTHROPIC_CUSTOM_HEADERS:
+                shellCustomHeaders || persistedCustomHeaders,
+            }
+          : {}),
       },
     })
   }
diff --git a/src/utils/providerProfiles.test.ts b/src/utils/providerProfiles.test.ts
index f14bb668c..515756816 100644
--- a/src/utils/providerProfiles.test.ts
+++ b/src/utils/providerProfiles.test.ts
@@ -19,6 +19,7 @@ const RESTORED_KEYS = [
   'CLAUDE_CODE_PROVIDER_PROFILE_ENV_APPLIED_ID',
   'CLAUDE_CODE_PROVIDER_ROUTE_ID',
   'CLAUDE_CONFIG_DIR',
+  'OPENCLAUDE_CONFIG_DIR',
   'CLAUDE_CODE_USE_OPENAI',
   'CLAUDE_CODE_USE_GEMINI',
   'CLAUDE_CODE_USE_MISTRAL',
@@ -45,6 +46,7 @@ const RESTORED_KEYS = [
   'ANTHROPIC_BASE_URL',
   'ANTHROPIC_MODEL',
   'ANTHROPIC_API_KEY',
+  'ANTHROPIC_AUTH_TOKEN',
   'ANTHROPIC_CUSTOM_HEADERS',
   'ANTHROPIC_VERTEX_BASE_URL',
   'GEMINI_BASE_URL',
@@ -109,6 +111,7 @@ beforeEach(async () => {
   }
   testConfigDir = mkdtempSync(join(tmpdir(), 'openclaude-provider-config-'))
   process.env.CLAUDE_CONFIG_DIR = testConfigDir
+  process.env.OPENCLAUDE_CONFIG_DIR = testConfigDir
 })
 
 afterEach(() => {
@@ -2254,6 +2257,20 @@ describe('getProviderPresetDefaults', () => {
 
     expect(defaults.apiKey).toBe('key-a,key-b')
   })
+
+  test('custom Anthropic preserves direct endpoint settings but only hydrates a Bearer token', async () => {
+    const { getProviderPresetDefaults } = await importFreshProviderProfileModules()
+    process.env.ANTHROPIC_BASE_URL = 'https://tenant.example/v1'
+    process.env.ANTHROPIC_MODEL = 'tenant-model'
+    process.env.ANTHROPIC_AUTH_TOKEN = 'bearer-token'
+    process.env.ANTHROPIC_API_KEY = 'native-api-key'
+
+    const defaults = getProviderPresetDefaults('custom-anthropic')
+
+    expect(defaults.baseUrl).toBe('https://tenant.example/v1')
+    expect(defaults.model).toBe('tenant-model')
+    expect(defaults.apiKey).toBe('bearer-token')
+  })
   test('ollama preset defaults to a local Ollama model', async () => {
     const { getProviderPresetDefaults } = await importFreshProviderProfileModules()
     delete process.env.OPENAI_MODEL
@@ -3236,6 +3253,44 @@ describe('setActiveProviderProfile', () => {
     }
   })
 
+  test('persists custom Anthropic-compatible profiles with Bearer token auth', async () => {
+    const tempDir = mkdtempSync(join(tmpdir(), 'openclaude-provider-'))
+    const configDir = mkdtempSync(join(tmpdir(), 'openclaude-provider-config-'))
+    process.chdir(tempDir)
+    process.env.CLAUDE_CONFIG_DIR = configDir
+
+    try {
+      const { setActiveProviderProfile } = await importFreshProviderProfileModules()
+      const profile = buildProfile({
+        id: 'custom_anthropic_prof',
+        name: 'Custom Anthropic',
+        provider: 'custom-anthropic',
+        baseUrl: 'https://anthropic-proxy.example',
+        model: 'claude-proxy-model',
+        apiKey: 'proxy-token',
+      })
+      saveMockGlobalConfig(current => ({ ...current, providerProfiles: [profile] }))
+
+      const result = setActiveProviderProfile('custom_anthropic_prof', { configDir })
+      const persisted = JSON.parse(readFileSync(join(configDir, '.openclaude-profile.json'), 'utf8'))
+
+      expect(result?.id).toBe('custom_anthropic_prof')
+      expect(process.env.ANTHROPIC_BASE_URL).toBe('https://anthropic-proxy.example')
+      expect(process.env.ANTHROPIC_MODEL).toBe('claude-proxy-model')
+      expect(process.env.ANTHROPIC_AUTH_TOKEN).toBe('proxy-token')
+      expect(process.env.ANTHROPIC_API_KEY).toBeUndefined()
+      expect(persisted.env).toEqual({
+        ANTHROPIC_BASE_URL: 'https://anthropic-proxy.example',
+        ANTHROPIC_MODEL: 'claude-proxy-model',
+        ANTHROPIC_AUTH_TOKEN: 'proxy-token',
+      })
+    } finally {
+      process.chdir(originalCwd)
+      rmSync(tempDir, { recursive: true, force: true })
+      rmSync(configDir, { recursive: true, force: true })
+    }
+  })
+
   test('sets ANTHROPIC_MODEL env var when switching to an anthropic-type provider', async () => {
     const { setActiveProviderProfile } =
       await importFreshProviderProfileModules()
@@ -3443,6 +3498,101 @@ describe('deleteProviderProfile', () => {
     expect(process.env.ANTHROPIC_API_KEY).toBeUndefined()
   })
 
+  test('deleting the active custom Anthropic profile removes its startup mirror', async () => {
+    const {
+      deleteProviderProfile,
+      setActiveProviderProfile,
+    } = await importFreshProviderProfileModules()
+    const profile = buildProfile({
+      id: 'custom_anthropic_profile',
+      provider: 'custom-anthropic',
+      baseUrl: 'https://proxy.example',
+      model: 'proxy-model',
+      apiKey: 'bearer-token',
+    })
+    saveMockGlobalConfig(current => ({
+      ...current,
+      providerProfiles: [profile],
+      activeProviderProfileId: profile.id,
+    }))
+
+    setActiveProviderProfile(profile.id, { configDir: testConfigDir ?? undefined })
+    const profilePath = join(testConfigDir!, '.openclaude-profile.json')
+    expect(existsSync(profilePath)).toBe(true)
+
+    deleteProviderProfile(profile.id)
+
+    expect(existsSync(profilePath)).toBe(false)
+  })
+
+  test('updating the active custom Anthropic profile synchronizes its startup mirror', async () => {
+    const { setActiveProviderProfile, updateProviderProfile } =
+      await importFreshProviderProfileModules()
+    const profile = buildProfile({
+      id: 'custom_anthropic_profile',
+      provider: 'custom-anthropic',
+      baseUrl: 'https://proxy.example',
+      model: 'proxy-model',
+      apiKey: 'old-token',
+    })
+    saveMockGlobalConfig(current => ({
+      ...current,
+      providerProfiles: [profile],
+      activeProviderProfileId: profile.id,
+    }))
+
+    setActiveProviderProfile(profile.id, { configDir: testConfigDir ?? undefined })
+    updateProviderProfile(profile.id, {
+      ...profile,
+      baseUrl: 'https://new-proxy.example',
+      model: 'new-proxy-model',
+      apiKey: 'new-token',
+    })
+
+    const persisted = JSON.parse(
+      readFileSync(join(testConfigDir!, '.openclaude-profile.json'), 'utf8'),
+    )
+    expect(persisted.env.ANTHROPIC_BASE_URL).toBe('https://new-proxy.example')
+    expect(persisted.env.ANTHROPIC_MODEL).toBe('new-proxy-model')
+    expect(persisted.env.ANTHROPIC_AUTH_TOKEN).toBe('new-token')
+  })
+
+  test('deleting an active custom Anthropic profile persists its replacement', async () => {
+    const { deleteProviderProfile, setActiveProviderProfile } =
+      await importFreshProviderProfileModules()
+    const activeProfile = buildProfile({
+      id: 'custom_anthropic_profile',
+      provider: 'custom-anthropic',
+      baseUrl: 'https://proxy.example',
+      model: 'proxy-model',
+      apiKey: 'bearer-token',
+    })
+    const replacement = buildProfile({
+      id: 'replacement_profile',
+      baseUrl: 'https://replacement.example/v1',
+      model: 'replacement-model',
+      apiKey: 'replacement-token',
+    })
+    saveMockGlobalConfig(current => ({
+      ...current,
+      providerProfiles: [activeProfile, replacement],
+      activeProviderProfileId: activeProfile.id,
+    }))
+
+    setActiveProviderProfile(activeProfile.id, {
+      configDir: testConfigDir ?? undefined,
+    })
+    deleteProviderProfile(activeProfile.id)
+
+    const persisted = JSON.parse(
+      readFileSync(join(testConfigDir!, '.openclaude-profile.json'), 'utf8'),
+    )
+    expect(persisted.profile).toBe('openai')
+    expect(persisted.env.OPENAI_BASE_URL).toBe('https://replacement.example/v1')
+    expect(persisted.env.OPENAI_MODEL).toBe('replacement-model')
+    expect(persisted.env.OPENAI_API_KEY).toBe('replacement-token')
+  })
+
   test('deleting final profile preserves explicit startup provider env', async () => {
     const { deleteProviderProfile } = await importFreshProviderProfileModules()
     process.env.CLAUDE_CODE_USE_OPENAI = '1'
diff --git a/src/utils/providerProfiles.ts b/src/utils/providerProfiles.ts
index 636d433bf..9351b1689 100644
--- a/src/utils/providerProfiles.ts
+++ b/src/utils/providerProfiles.ts
@@ -212,13 +212,16 @@ function resolveProfileCapabilityRouteId(
   provider: string,
   baseUrl?: string,
 ): string {
+  const providerRouteId = resolveProfileRoute(provider).routeId
+  if (providerRouteId === 'custom-anthropic') {
+    return providerRouteId
+  }
+
   const routeIdFromBaseUrl = resolveRouteIdFromBaseUrl(baseUrl)
   if (routeIdFromBaseUrl) {
     return routeIdFromBaseUrl
   }
 
-  const providerRouteId = resolveProfileRoute(provider).routeId
-
   // A cloudflare profile retargeted away from the real Workers AI endpoint
   // (e.g. to gateway.ai.cloudflare.com or another OpenAI-compatible host) is
   // run generically at runtime — resolveActiveRouteIdFromEnv no longer resolves
@@ -405,6 +408,16 @@ function applySupportedProfileCustomHeaders(
   return customHeaders ? { ...env, ANTHROPIC_CUSTOM_HEADERS: customHeaders } : env
 }
 
+function buildAnthropicCredentialEnv(
+  provider: ProviderProfile['provider'],
+  apiKey: string | undefined,
+): ProfileEnv {
+  if (!apiKey) return {}
+  return provider === 'custom-anthropic'
+    ? { ANTHROPIC_AUTH_TOKEN: apiKey }
+    : { ANTHROPIC_API_KEY: apiKey }
+}
+
 function getModelCacheByProfile(
   profileId: string,
   config = getGlobalConfig(),
@@ -444,7 +457,7 @@ export function getProviderPresetDefaults(
   // Keep preset-pinned endpoints/models even when generic OpenAI env values
   // are present, but still read provider-specific credential env vars above.
   const routeDefaults =
-    preset === 'custom'
+    preset === 'custom' || preset === 'custom-anthropic'
       ? metadata
       : getProviderPresetUiMetadata(preset, {})
   return {
@@ -452,7 +465,13 @@ export function getProviderPresetDefaults(
     name: metadata.name,
     baseUrl: routeDefaults.baseUrl,
     model: routeDefaults.model,
-    apiKey: metadata.apiKey,
+    // The /provider custom Anthropic flow always saves a Bearer token. Keep
+    // direct ANTHROPIC_API_KEY/x-api-key setups out of that field so opening
+    // the preset cannot silently change their authentication scheme.
+    apiKey:
+      preset === 'custom-anthropic'
+        ? process.env.ANTHROPIC_AUTH_TOKEN?.trim() || undefined
+        : metadata.apiKey,
     requiresApiKey: metadata.requiresApiKey,
   }
 }
@@ -499,6 +518,14 @@ function hasCompleteProviderSelection(
   processEnv: NodeJS.ProcessEnv = process.env,
 ): boolean {
   if (resolveEnvOnlyProviderRouteId(processEnv) !== null) return true
+  if (
+    trimOrUndefined(processEnv.ANTHROPIC_BASE_URL) !== undefined &&
+    trimOrUndefined(processEnv.ANTHROPIC_MODEL) !== undefined &&
+    (trimOrUndefined(processEnv.ANTHROPIC_AUTH_TOKEN) !== undefined ||
+      trimOrUndefined(processEnv.ANTHROPIC_API_KEY) !== undefined)
+  ) {
+    return true
+  }
   if (!hasProviderSelectionFlags(processEnv)) return false
   if (processEnv.CLAUDE_CODE_USE_OPENAI !== undefined) {
     return (
@@ -591,7 +618,9 @@ function isProcessEnvAlignedWithProfile(
       sameOptionalEnvValue(processEnv.ANTHROPIC_BASE_URL, profile.baseUrl) &&
       sameOptionalEnvValue(processEnv.ANTHROPIC_MODEL, primaryModel) &&
       (!includeApiKey ||
-        sameOptionalEnvValue(processEnv.ANTHROPIC_API_KEY, profile.apiKey))
+        (profile.provider === 'custom-anthropic'
+          ? sameOptionalEnvValue(processEnv.ANTHROPIC_AUTH_TOKEN, profile.apiKey)
+          : sameOptionalEnvValue(processEnv.ANTHROPIC_API_KEY, profile.apiKey)))
     )
   }
 
@@ -838,7 +867,7 @@ export function applyProviderProfileToProcessEnv(
       profileEnv = {
         ANTHROPIC_BASE_URL: profile.baseUrl,
         ANTHROPIC_MODEL: primaryModel,
-        ...(profile.apiKey ? { ANTHROPIC_API_KEY: profile.apiKey } : {}),
+        ...buildAnthropicCredentialEnv(profile.provider, profile.apiKey),
       }
     }
   } else if (compatibilityMode === 'mistral') {
@@ -1185,7 +1214,7 @@ export function updateProviderProfile(
   }
 
   if (shouldApply) {
-    applyProviderProfileToProcessEnv(updatedProfile)
+    setActiveProviderProfile(profileId)
   }
 
   return updatedProfile
@@ -1398,9 +1427,10 @@ function buildStartupProfileFromActiveProfile(
         env: applySupportedProfileCustomHeaders(activeProfile, {
           ANTHROPIC_BASE_URL: activeProfile.baseUrl,
           ANTHROPIC_MODEL: getPrimaryModel(activeProfile.model),
-          ...(activeProfile.apiKey
-            ? { ANTHROPIC_API_KEY: activeProfile.apiKey }
-            : {}),
+          ...buildAnthropicCredentialEnv(
+            activeProfile.provider,
+            activeProfile.apiKey,
+          ),
         }),
       }
     case 'gemini': {
@@ -1626,6 +1656,7 @@ export function deleteProviderProfile(profileId: string): {
   let removed = false
   let deletedProfile: ProviderProfile | undefined
   let nextActiveProfile: ProviderProfile | undefined
+  let activeProfileWasDeleted = false
 
   saveGlobalConfig(current => {
     const currentProfiles = getProviderProfiles(current)
@@ -1648,6 +1679,7 @@ export function deleteProviderProfile(profileId: string): {
       currentActive === profileId ||
       (currentActive !== ANTHROPIC_DEFAULT_PROFILE_ID &&
         !nextProfiles.some(profile => profile.id === currentActive))
+    activeProfileWasDeleted = activeWasDeleted
 
     const nextActiveId = activeWasDeleted ? nextProfiles[0]?.id : currentActive
 
@@ -1682,14 +1714,16 @@ export function deleteProviderProfile(profileId: string): {
   })
 
   if (nextActiveProfile) {
-    applyProviderProfileToProcessEnv(nextActiveProfile)
-  } else if (
-    deletedProfile &&
-    isProcessEnvAlignedWithProfile(process.env, deletedProfile, {
-      includeApiKey: false,
-    })
-  ) {
-    clearProviderProfileEnvFromProcessEnv()
+    setActiveProviderProfile(nextActiveProfile.id)
+  } else if (deletedProfile && activeProfileWasDeleted) {
+    if (
+      isProcessEnvAlignedWithProfile(process.env, deletedProfile, {
+        includeApiKey: false,
+      })
+    ) {
+      clearProviderProfileEnvFromProcessEnv()
+    }
+    deleteProfileFile()
   }
 
   return {
diff --git a/src/utils/providerStartupOverrides.test.ts b/src/utils/providerStartupOverrides.test.ts
index 8082de709..c6d9e444f 100644
--- a/src/utils/providerStartupOverrides.test.ts
+++ b/src/utils/providerStartupOverrides.test.ts
@@ -17,6 +17,7 @@ describe('clearStartupProviderOverrides', () => {
           OPENAI_API_KEY: 'single-key',
           MINIMAX_API_KEY: 'sk-minimax',
           VENICE_API_KEY: 'sk-venice',
+          ANTHROPIC_AUTH_TOKEN: 'stale-proxy-token',
           KEEP_ME: '1',
         },
       }),
@@ -39,6 +40,7 @@ describe('clearStartupProviderOverrides', () => {
           OPENAI_API_KEY: undefined,
           MINIMAX_API_KEY: undefined,
           VENICE_API_KEY: undefined,
+          ANTHROPIC_AUTH_TOKEN: undefined,
         }),
       }),
     )
diff --git a/src/utils/providerStartupOverrides.ts b/src/utils/providerStartupOverrides.ts
index b39b0e125..29af28e29 100644
--- a/src/utils/providerStartupOverrides.ts
+++ b/src/utils/providerStartupOverrides.ts
@@ -20,6 +20,7 @@ export const STARTUP_PROVIDER_OVERRIDE_ENV_KEYS = [
   'ANTHROPIC_BASE_URL',
   'ANTHROPIC_MODEL',
   'ANTHROPIC_API_KEY',
+  'ANTHROPIC_AUTH_TOKEN',
   'ANTHROPIC_CUSTOM_HEADERS',
   'GEMINI_API_KEY',
   'GOOGLE_API_KEY',
diff --git a/src/utils/statusNoticeDefinitions.tsx b/src/utils/statusNoticeDefinitions.tsx
index 62570fe5c..9899822f4 100644
--- a/src/utils/statusNoticeDefinitions.tsx
+++ b/src/utils/statusNoticeDefinitions.tsx
@@ -15,7 +15,7 @@ import { isJetBrainsPluginInstalledCachedSync } from './jetbrains.js';
 import type { LocalModelContextWarning } from './statusNoticeLocalModel.js';
 import type { PermissionMode } from './permissions/PermissionMode.js';
 import { modelSupportsAutoMode } from './betas.js';
-import { getAPIProvider } from './model/providers.js';
+import { getAPIProvider, isFirstPartyAnthropicBaseUrl } from './model/providers.js';
 import { logForDebugging } from './debug.js';
 
 // Types
@@ -269,7 +269,7 @@ const thirdPartyPermissiveModeNotice: StatusNoticeDefinition = {
     if (ctx.mainLoopModel && modelSupportsAutoMode(ctx.mainLoopModel)) {
       return false;
     }
-    return getAPIProvider() !== 'firstParty';
+    return getAPIProvider() !== 'firstParty' || !isFirstPartyAnthropicBaseUrl();
   },
   render: ctx => {
     const mode = ctx.permissionMode;
diff --git a/src/utils/thinking.ts b/src/utils/thinking.ts
index 86320faef..774231bc5 100644
--- a/src/utils/thinking.ts
+++ b/src/utils/thinking.ts
@@ -10,7 +10,9 @@ import {
 import { getCanonicalName } from './model/model.js'
 import { resolveAntModel } from './model/antModels.js'
 import { get3PModelCapabilityOverride } from './model/modelSupportOverrides.js'
-import { getAPIProvider } from './model/providers.js'
+import {
+  getAPIProvider,
+} from './model/providers.js'
 import { getSettingsWithErrors } from './settings/settings.js'
 import { isEnvTruthy } from './envUtils.js'