From 6d9a3a9364c4c846ef0093f6633f9b35c38b3a39 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E7=A8=8B=E5=BA=8F=E5=91=98=E9=98=BF=E6=B1=9F=28Relakkes?=
 =?UTF-8?q?=29?= <relakkes@gmail.com>
Date: Tue, 29 Sep 2026 16:25:20 +0800
Subject: [PATCH] feat(models): support Sonnet 5.5 and refresh Claude defaults

---
 .../chat/PlanModePermissionDialog.test.tsx    |   5 +-
 .../controls/ModelSelector.test.tsx           |  24 +-
 desktop/src/constants/modelCatalog.test.ts    |  15 +
 desktop/src/constants/modelCatalog.ts         |   8 +
 src/constants/prompts.ts                      |  32 ++-
 src/server/__tests__/conversations.test.ts    |   4 +-
 .../__tests__/e2e/business-flow.test.ts       |   5 +-
 src/server/__tests__/e2e/full-flow.test.ts    |   2 +-
 src/server/__tests__/settings.test.ts         |  34 ++-
 src/server/api/models.ts                      |  13 +-
 .../services/claudeOfficialRuntime.test.ts    |  29 +-
 src/server/services/claudeOfficialRuntime.ts  |   2 +-
 .../services/localIndex/coordinator.test.ts   |  95 +++++++
 .../services/localIndex/sessionProjector.ts   |   4 +-
 .../api/claudeRequiredThinking.test.ts        |  20 ++
 src/skills/bundled/claudeApiContent.ts        |  10 +-
 src/utils/commitAttribution.ts                |   1 +
 src/utils/context.ts                          |   2 +-
 src/utils/effort.ts                           |   5 +-
 src/utils/model/configs.ts                    |   9 +
 src/utils/model/fable.test.ts                 |  48 +++-
 src/utils/model/model.ts                      |  33 ++-
 src/utils/model/modelContextWindows.ts        |   1 +
 src/utils/model/modelOptions.ts               |  43 +--
 src/utils/model/opus5.test.ts                 |  63 ++++-
 src/utils/model/sonnet55.test.ts              | 256 ++++++++++++++++++
 src/utils/modelCost.ts                        |  30 +-
 src/utils/modelCostParity.test.ts             |  42 +++
 src/utils/thinking.ts                         |  21 +-
 src/utils/usageAccounting.test.ts             |  79 +++++-
 src/utils/usageAccounting.ts                  |   9 +-
 31 files changed, 842 insertions(+), 102 deletions(-)
 create mode 100644 src/utils/model/sonnet55.test.ts
 create mode 100644 src/utils/modelCostParity.test.ts

diff --git a/desktop/src/components/chat/PlanModePermissionDialog.test.tsx b/desktop/src/components/chat/PlanModePermissionDialog.test.tsx
index c61fb119..c5c78225 100644
--- a/desktop/src/components/chat/PlanModePermissionDialog.test.tsx
+++ b/desktop/src/components/chat/PlanModePermissionDialog.test.tsx
@@ -389,7 +389,8 @@ describe('plan mode permission UI', () => {
     await waitFor(() => {
       expect(screen.getByTestId('model-selector-dropdown')).toBeTruthy()
     })
-    fireEvent.click(screen.getByRole('button', { name: /Sonnet 5/ }))
+    // Anchored so the official catalog's "Sonnet 5.5" is not also matched.
+    fireEvent.click(screen.getByRole('button', { name: /^Sonnet 5(?![.\d])/ }))
 
     await waitFor(() => {
       expect(screen.getByTestId('plan-execution-model').textContent).toContain('applies on approve')
@@ -445,7 +446,7 @@ describe('plan mode permission UI', () => {
     await waitFor(() => {
       expect(screen.getByTestId('model-selector-dropdown')).toBeTruthy()
     })
-    fireEvent.click(screen.getByRole('button', { name: /Sonnet 5/ }))
+    fireEvent.click(screen.getByRole('button', { name: /^Sonnet 5(?![.\d])/ }))
     await waitFor(() => {
       expect(screen.getByTestId('plan-execution-model').textContent).toContain('applies on approve')
     })
diff --git a/desktop/src/components/controls/ModelSelector.test.tsx b/desktop/src/components/controls/ModelSelector.test.tsx
index 2b85c717..6dc35d7d 100644
--- a/desktop/src/components/controls/ModelSelector.test.tsx
+++ b/desktop/src/components/controls/ModelSelector.test.tsx
@@ -194,7 +194,7 @@ describe('ModelSelector', () => {
     },
   )
 
-  it('keeps the current Claude Official catalog visible when the API returns legacy settings models', async () => {
+  function renderClaudeOfficialWithLegacyModels() {
     const legacyModels: ModelInfo[] = [
       { id: 'claude-opus-4-7', name: 'Opus 4.7', description: 'Legacy Opus', context: '1m' },
       { id: 'claude-sonnet-4-6', name: 'Sonnet 4.6', description: 'Legacy Sonnet', context: '200k' },
@@ -224,6 +224,11 @@ describe('ModelSelector', () => {
 
     const onRuntimeChange = vi.fn()
     render(<ModelSelector runtimeKey="session-claude-legacy" onRuntimeSelectionChange={onRuntimeChange} />)
+    return onRuntimeChange
+  }
+
+  it('keeps the current Claude Official catalog visible when the API returns legacy settings models', async () => {
+    const onRuntimeChange = renderClaudeOfficialWithLegacyModels()
 
     await clickByRole(/Opus 4\.7/i)
 
@@ -231,7 +236,8 @@ describe('ModelSelector', () => {
     expect(screen.getByRole('button', { name: /Opus 5\.5/ })).toBeInTheDocument()
     expect(screen.getByRole('button', { name: /^Opus 5 / })).toBeInTheDocument()
     expect(screen.getByRole('button', { name: /Opus 4\.8/ })).toBeInTheDocument()
-    expect(screen.getByRole('button', { name: /Sonnet 5/ })).toBeInTheDocument()
+    expect(screen.getByRole('button', { name: /Sonnet 5\.5/ })).toBeInTheDocument()
+    expect(screen.getByRole('button', { name: /^Sonnet 5 / })).toBeInTheDocument()
     expect(screen.getAllByRole('button', { name: /Opus 4\.7/ }).length).toBeGreaterThan(0)
     await clickByRole(/Opus 5\.5/)
     expect(onRuntimeChange).toHaveBeenCalledWith(expect.objectContaining({
@@ -239,6 +245,20 @@ describe('ModelSelector', () => {
     }))
   })
 
+  it('selects Sonnet 5.5 from the Claude Official catalog instead of the Sonnet 5 it supersedes', async () => {
+    const onRuntimeChange = renderClaudeOfficialWithLegacyModels()
+
+    await clickByRole(/Opus 4\.7/i)
+    await clickByRole(/Sonnet 5\.5/)
+
+    expect(onRuntimeChange).toHaveBeenCalledWith(expect.objectContaining({
+      providerId: null, modelId: 'claude-sonnet-5-5',
+    }))
+    expect(onRuntimeChange).not.toHaveBeenCalledWith(expect.objectContaining({
+      modelId: 'claude-sonnet-5',
+    }))
+  })
+
   it('does not query official OAuth status when mounted', () => {
     const fetchClaudeStatus = vi.fn(async () => {})
     const fetchOpenAIStatus = vi.fn(async () => {})
diff --git a/desktop/src/constants/modelCatalog.test.ts b/desktop/src/constants/modelCatalog.test.ts
index f876f9c5..4321e8a2 100644
--- a/desktop/src/constants/modelCatalog.test.ts
+++ b/desktop/src/constants/modelCatalog.test.ts
@@ -12,6 +12,21 @@ describe('Claude official model catalog', () => {
     })
   })
 
+  it('offers Sonnet 5.5 with the Claude Code default effort and context for OAuth selection', () => {
+    expect(OFFICIAL_MODELS.find(model => model.id === 'claude-sonnet-5-5')).toMatchObject({
+      name: 'Sonnet 5.5',
+      context: '1m',
+      defaultReasoningEffort: 'medium',
+      supportedReasoningEfforts: ['low', 'medium', 'high', 'xhigh', 'max'],
+    })
+  })
+
+  it('lists Sonnet 5.5 ahead of the Sonnet 5 it supersedes', () => {
+    const ids = OFFICIAL_MODELS.map(model => model.id)
+    expect(ids.indexOf('claude-sonnet-5-5')).toBeGreaterThanOrEqual(0)
+    expect(ids.indexOf('claude-sonnet-5-5')).toBeLessThan(ids.indexOf('claude-sonnet-5'))
+  })
+
   it('keeps older explicit model selections available', () => {
     expect(OFFICIAL_MODELS.map(model => model.id)).toEqual(expect.arrayContaining([
       'claude-opus-5', 'claude-opus-4-8', 'claude-fable-5-1', 'claude-sonnet-5',
diff --git a/desktop/src/constants/modelCatalog.ts b/desktop/src/constants/modelCatalog.ts
index 49339f52..d39cffdc 100644
--- a/desktop/src/constants/modelCatalog.ts
+++ b/desktop/src/constants/modelCatalog.ts
@@ -41,6 +41,14 @@ export const OFFICIAL_MODELS: ModelInfo[] = [
     defaultReasoningEffort: 'high',
     supportedReasoningEfforts: ['low', 'medium', 'high', 'xhigh', 'max'],
   },
+  {
+    id: 'claude-sonnet-5-5',
+    name: 'Sonnet 5.5',
+    description: 'Best combination of speed and intelligence',
+    context: '1m',
+    defaultReasoningEffort: 'medium',
+    supportedReasoningEfforts: ['low', 'medium', 'high', 'xhigh', 'max'],
+  },
   {
     id: 'claude-sonnet-5',
     name: 'Sonnet 5',
diff --git a/src/constants/prompts.ts b/src/constants/prompts.ts
index 23e62bac..a51bd73a 100644
--- a/src/constants/prompts.ts
+++ b/src/constants/prompts.ts
@@ -114,15 +114,14 @@ export const CLAUDE_CODE_DOCS_MAP_URL =
 export const SYSTEM_PROMPT_DYNAMIC_BOUNDARY =
   '__SYSTEM_PROMPT_DYNAMIC_BOUNDARY__'
 
-// @[MODEL LAUNCH]: Update the latest frontier model.
-const FRONTIER_MODEL_NAME = 'Claude Opus 4.8'
-
-// @[MODEL LAUNCH]: Update the model family IDs below to the latest in each tier.
+// @[MODEL LAUNCH]: Update the model family IDs below to the latest in each tier, and the
+// matching names in the "most recent Claude models" sentence in computeSimpleEnvInfo.
+// The Haiku ID is the pinned snapshot, as in the official Claude Code prompt.
 const LATEST_CLAUDE_MODEL_IDS = {
-  fable: 'claude-fable-5',
-  opus: 'claude-opus-4-8',
-  sonnet: 'claude-sonnet-5',
-  haiku: 'claude-haiku-4-5',
+  fable: 'claude-fable-5-1',
+  opus: 'claude-opus-5-5',
+  sonnet: 'claude-sonnet-5-5',
+  haiku: 'claude-haiku-4-5-20251001',
 }
 
 function getHooksSection(): string {
@@ -694,13 +693,13 @@ export async function computeSimpleEnvInfo(
     knowledgeCutoffMessage,
     process.env.USER_TYPE === 'ant' && isUndercover()
       ? null
-      : `The most recent Claude flagship models are Claude Fable 5, Claude Opus 4.8, Claude Sonnet 5, and Claude Haiku 4.5. Model IDs — Fable 5: '${LATEST_CLAUDE_MODEL_IDS.fable}', Opus 4.8: '${LATEST_CLAUDE_MODEL_IDS.opus}', Sonnet 5: '${LATEST_CLAUDE_MODEL_IDS.sonnet}', Haiku 4.5: '${LATEST_CLAUDE_MODEL_IDS.haiku}'. When building AI applications, default to the latest and most capable Claude models.`,
+      : `The most recent Claude models are the Claude 5 family and Haiku 4.5. Model IDs — Fable 5.1: '${LATEST_CLAUDE_MODEL_IDS.fable}', Opus 5.5: '${LATEST_CLAUDE_MODEL_IDS.opus}', Sonnet 5.5: '${LATEST_CLAUDE_MODEL_IDS.sonnet}', Haiku 4.5: '${LATEST_CLAUDE_MODEL_IDS.haiku}'. When building AI applications, default to the latest and most capable Claude models.`,
     process.env.USER_TYPE === 'ant' && isUndercover()
       ? null
       : `Claude Code is available as a CLI in the terminal, desktop app (Mac/Windows), web app (claude.ai/code), and IDE extensions (VS Code, JetBrains).`,
     process.env.USER_TYPE === 'ant' && isUndercover()
       ? null
-      : `Fast mode for Claude Code uses the same ${FRONTIER_MODEL_NAME} model with faster output. It does NOT switch to a different model. It can be toggled with /fast.`,
+      : `Fast mode for Claude Code uses Claude Opus with faster output (it does not downgrade to a smaller model). It can be toggled with /fast.`,
   ].filter(item => item !== null)
 
   return [
@@ -713,16 +712,25 @@ export async function computeSimpleEnvInfo(
 // @[MODEL LAUNCH]: Add a knowledge cutoff date for the new model.
 function getKnowledgeCutoff(modelId: string): string | null {
   const canonical = getCanonicalName(modelId)
+  // Order matters: a point release (`-5-5`, `-5-1`) contains its whole-number id, so it is
+  // matched first. Values follow Anthropic's model pages and the official Claude Code catalog.
   if (
+    canonical.includes('claude-fable-5-1') ||
+    canonical.includes('claude-opus-5-5') ||
+    canonical.includes('claude-sonnet-5-5')
+  ) {
+    return 'June 2026'
+  } else if (canonical.includes('claude-opus-5')) {
+    return 'May 2026'
+  } else if (
     canonical.includes('claude-fable-5') ||
     canonical.includes('claude-opus-4-8') ||
+    canonical.includes('claude-opus-4-7') ||
     canonical.includes('claude-sonnet-5')
   ) {
     return 'January 2026'
   } else if (canonical.includes('claude-sonnet-4-6')) {
     return 'August 2025'
-  } else if (canonical.includes('claude-opus-4-7')) {
-    return 'May 2025'
   } else if (canonical.includes('claude-opus-4-5')) {
     return 'May 2025'
   } else if (canonical.includes('claude-haiku-4')) {
diff --git a/src/server/__tests__/conversations.test.ts b/src/server/__tests__/conversations.test.ts
index 0b5099b7..5f58c185 100644
--- a/src/server/__tests__/conversations.test.ts
+++ b/src/server/__tests__/conversations.test.ts
@@ -3570,12 +3570,12 @@ describe('WebSocket Chat Integration', () => {
         sessionId,
         options: {
           providerId: null,
-          model: 'claude-sonnet-5',
+          model: 'claude-sonnet-5-5',
         },
       })
       await expect(sessionService.getSessionLaunchInfo(sessionId)).resolves.toMatchObject({
         runtimeProviderId: null,
-        runtimeModelId: 'claude-sonnet-5',
+        runtimeModelId: 'claude-sonnet-5-5',
       })
     } finally {
       conversationService.startSession = originalStartSession
diff --git a/src/server/__tests__/e2e/business-flow.test.ts b/src/server/__tests__/e2e/business-flow.test.ts
index 2ddffeef..58645edb 100644
--- a/src/server/__tests__/e2e/business-flow.test.ts
+++ b/src/server/__tests__/e2e/business-flow.test.ts
@@ -374,20 +374,21 @@ describe('Business Flow: Models & Effort', () => {
 
   it('should return available fallback models', async () => {
     const { data } = await api('GET', '/api/models')
-    expect(data.models.length).toBe(7)
+    expect(data.models.length).toBe(8)
     const names = data.models.map((m: any) => m.name)
     expect(names).toContain('Fable 5.1')
     expect(names).toContain('Fable 5')
     expect(names).toContain('Opus 5.5')
     expect(names).toContain('Opus 5')
     expect(names).toContain('Opus 4.8')
+    expect(names).toContain('Sonnet 5.5')
     expect(names).toContain('Sonnet 5')
     expect(names).toContain('Haiku 4.5')
   })
 
   it('should default to Opus model', async () => {
     const { data } = await api('GET', '/api/models/current')
-    expect(data.model.id).toBe('claude-opus-5')
+    expect(data.model.id).toBe('claude-opus-5-5')
   })
 
   it('should switch to Opus 4.8', async () => {
diff --git a/src/server/__tests__/e2e/full-flow.test.ts b/src/server/__tests__/e2e/full-flow.test.ts
index 7c7ebd64..2a5268f0 100644
--- a/src/server/__tests__/e2e/full-flow.test.ts
+++ b/src/server/__tests__/e2e/full-flow.test.ts
@@ -216,7 +216,7 @@ describe('E2E: Full Flow', () => {
 
   it('should list available models', async () => {
     const { data } = await api('GET', '/api/models')
-    expect(data.models.length).toBe(7)
+    expect(data.models.length).toBe(8)
     expect(data.models[0].name).toBe('Fable 5.1')
   })
 
diff --git a/src/server/__tests__/settings.test.ts b/src/server/__tests__/settings.test.ts
index 0ee5930b..5f8b466c 100644
--- a/src/server/__tests__/settings.test.ts
+++ b/src/server/__tests__/settings.test.ts
@@ -968,6 +968,14 @@ describe('Models API', () => {
         defaultReasoningEffort: 'high',
         supportedReasoningEfforts: ['low', 'medium', 'high', 'xhigh', 'max'],
       },
+      {
+        id: 'claude-sonnet-5-5',
+        name: 'Sonnet 5.5',
+        description: 'Best combination of speed and intelligence',
+        context: '1m',
+        defaultReasoningEffort: 'medium',
+        supportedReasoningEfforts: ['low', 'medium', 'high', 'xhigh', 'max'],
+      },
       {
         id: 'claude-sonnet-5',
         name: 'Sonnet 5',
@@ -1177,7 +1185,8 @@ describe('Models API', () => {
 
     expect(res.status).toBe(200)
     const body = await res.json()
-    expect(body.model.id).toBe('claude-opus-5')
+    // The CLI launches without an explicit model here and its `opus` alias is Opus 5.5.
+    expect(body.model).toMatchObject({ id: 'claude-opus-5-5', name: 'Opus 5.5' })
   })
 
   it('GET /api/models/current should replace the legacy opus[1m] default with the Claude OAuth Pro default', async () => {
@@ -1200,8 +1209,9 @@ describe('Models API', () => {
     const currentBody = await currentResponse.json()
 
     expect(currentBody.model).toMatchObject({
-      id: 'claude-sonnet-5',
-      name: 'Sonnet 5',
+      id: 'claude-sonnet-5-5',
+      name: 'Sonnet 5.5',
+      defaultReasoningEffort: 'medium',
     })
 
     const listRequest = makeRequest('GET', '/api/models')
@@ -1217,6 +1227,7 @@ describe('Models API', () => {
       'claude-opus-5-5',
       'claude-opus-5',
       'claude-opus-4-8',
+      'claude-sonnet-5-5',
       'claude-sonnet-5',
       'claude-haiku-4-5',
     ])
@@ -1574,16 +1585,17 @@ describe('Model Options', () => {
   beforeEach(setup)
   afterEach(teardown)
 
-  it('defaults Anthropic API users to Opus 5 and exposes the current official options once', () => {
+  it('defaults Anthropic API users to Opus 5.5 and exposes the current official options once', () => {
     process.env.ANTHROPIC_API_KEY = 'test-api-key'
 
-    expect(getDefaultMainLoopModelSetting()).toBe('claude-opus-5')
+    expect(getDefaultMainLoopModelSetting()).toBe('claude-opus-5-5')
 
     const options = getModelOptions()
     const values = options.map(option => option.value)
 
-    expect(options[0]?.description).toContain('Opus 5')
-    expect(options[0]?.description).toContain('$5')
+    expect(options[0]?.description).toContain('Opus 5.5')
+    // Opus 5.5 is $4/$20, not the $5/$25 of the Opus 5 it replaces as the default.
+    expect(options[0]?.description).toContain('$4/$20 per Mtok')
     expect(values).toContain('fable')
     expect(values).toContain('sonnet')
     expect(values).not.toContain('opus')
@@ -1623,10 +1635,10 @@ describe('Model Options', () => {
   it('labels extended-context options with current first-party and conservative third-party names', () => {
     process.env.ANTHROPIC_API_KEY = 'test-api-key'
 
-    expect(getSonnet46_1MOption().description).toContain('Sonnet 5')
-    expect(getOpus46_1MOption().description).toContain('Opus 5')
-    expect(getMaxSonnet46_1MOption().description).toContain('Sonnet 5')
-    expect(getMaxOpus46_1MOption().description).toContain('Opus 5')
+    expect(getSonnet46_1MOption().description).toContain('Sonnet 5.5')
+    expect(getOpus46_1MOption().description).toContain('Opus 5.5')
+    expect(getMaxSonnet46_1MOption().description).toContain('Sonnet 5.5')
+    expect(getMaxOpus46_1MOption().description).toContain('Opus 5.5')
 
     process.env.ANTHROPIC_BASE_URL = 'https://api.deepseek.com/anthropic'
 
diff --git a/src/server/api/models.ts b/src/server/api/models.ts
index aef44ff2..b9af8ae5 100644
--- a/src/server/api/models.ts
+++ b/src/server/api/models.ts
@@ -89,6 +89,14 @@ const DEFAULT_MODELS = [
     defaultReasoningEffort: 'high',
     supportedReasoningEfforts: ['low', 'medium', 'high', 'xhigh', 'max'],
   },
+  {
+    id: 'claude-sonnet-5-5',
+    name: 'Sonnet 5.5',
+    description: 'Best combination of speed and intelligence',
+    context: '1m',
+    defaultReasoningEffort: 'medium',
+    supportedReasoningEfforts: ['low', 'medium', 'high', 'xhigh', 'max'],
+  },
   {
     id: 'claude-sonnet-5',
     name: 'Sonnet 5',
@@ -107,7 +115,10 @@ const DEFAULT_MODELS = [
 
 const EFFORT_LEVELS = MODEL_REASONING_EFFORTS
 
-const DEFAULT_MODEL = 'claude-opus-5'
+// Standalone sessions (no provider, no Claude OAuth) start the CLI without an explicit model, so the
+// CLI's own default runs. Keep this in step with what the `opus` alias resolves to there
+// (getDefaultOpusModel) so the UI names the model that actually runs.
+const DEFAULT_MODEL = 'claude-opus-5-5'
 const DEFAULT_EFFORT = 'max'
 
 const settingsService = new SettingsService()
diff --git a/src/server/services/claudeOfficialRuntime.test.ts b/src/server/services/claudeOfficialRuntime.test.ts
index dfd29b4f..e86ecc76 100644
--- a/src/server/services/claudeOfficialRuntime.test.ts
+++ b/src/server/services/claudeOfficialRuntime.test.ts
@@ -23,10 +23,33 @@ describe('Claude official runtime model selection', () => {
     })
   }
 
-  test('selects Opus 5.5 for Max and preserves the Sonnet default for other subscriptions', () => {
+  function useProSubscription() {
+    tokenSpy.mockResolvedValue({
+      accessToken: 'fake-access-token',
+      refreshToken: null,
+      expiresAt: null,
+      scopes: [],
+      subscriptionType: 'pro',
+    })
+  }
+
+  test('selects Opus 5.5 for Max and Sonnet 5.5 for other subscriptions', () => {
     expect(getClaudeOfficialDefaultModelId('max')).toBe('claude-opus-5-5')
-    expect(getClaudeOfficialDefaultModelId('pro')).toBe('claude-sonnet-5')
-    expect(getClaudeOfficialDefaultModelId(null)).toBe('claude-sonnet-5')
+    expect(getClaudeOfficialDefaultModelId('pro')).toBe('claude-sonnet-5-5')
+    expect(getClaudeOfficialDefaultModelId(null)).toBe('claude-sonnet-5-5')
+  })
+
+  test('resolves Sonnet aliases and the unset default to Sonnet 5.5', async () => {
+    useProSubscription()
+    for (const model of [undefined, 'sonnet', 'sonnet[1m]', 'SONNET:1m', 'claude-sonnet-5-5[1m]']) {
+      expect(await resolveClaudeOfficialRuntimeModel(model)).toBe('claude-sonnet-5-5')
+    }
+  })
+
+  test('preserves an explicitly selected Sonnet 5 instead of rewriting it to Sonnet 5.5', async () => {
+    useProSubscription()
+    expect(await resolveClaudeOfficialRuntimeModel('claude-sonnet-5')).toBe('claude-sonnet-5')
+    expect(await resolveClaudeOfficialRuntimeModel('claude-sonnet-5[1m]')).toBe('claude-sonnet-5')
   })
 
   test('resolves Opus aliases and legacy defaults to Opus 5.5', async () => {
diff --git a/src/server/services/claudeOfficialRuntime.ts b/src/server/services/claudeOfficialRuntime.ts
index 4cff2724..3cf9f7e7 100644
--- a/src/server/services/claudeOfficialRuntime.ts
+++ b/src/server/services/claudeOfficialRuntime.ts
@@ -3,7 +3,7 @@ import type { ModelMapping } from '../types/provider.js'
 import { hahaOAuthService } from './hahaOAuthService.js'
 
 export const CLAUDE_OFFICIAL_OPUS_MODEL_ID = 'claude-opus-5-5'
-export const CLAUDE_OFFICIAL_SONNET_MODEL_ID = 'claude-sonnet-5'
+export const CLAUDE_OFFICIAL_SONNET_MODEL_ID = 'claude-sonnet-5-5'
 
 export const CLAUDE_OFFICIAL_DEFAULT_MODELS: ModelMapping = {
   main: CLAUDE_OFFICIAL_OPUS_MODEL_ID,
diff --git a/src/server/services/localIndex/coordinator.test.ts b/src/server/services/localIndex/coordinator.test.ts
index 4edff93f..142a9058 100644
--- a/src/server/services/localIndex/coordinator.test.ts
+++ b/src/server/services/localIndex/coordinator.test.ts
@@ -1,4 +1,5 @@
 import { afterEach, describe, expect, it } from 'bun:test'
+import { Database } from 'bun:sqlite'
 import { getEventListeners } from 'node:events'
 import { appendFile, chmod, mkdir, mkdtemp, readdir, rm, stat, symlink, writeFile } from 'node:fs/promises'
 import { tmpdir } from 'node:os'
@@ -777,6 +778,100 @@ describe('local index coordinator', () => {
     }
   })
 
+  it('replaces persisted per-model dollars with the current rates after a parser upgrade', async () => {
+    // Version 9 corrected the Sonnet 5 / Sonnet 5.5 / Opus 5.5 rates. Dollars are persisted per model,
+    // so without a parser bump every already-indexed transcript would keep its old price forever.
+    expect(SESSION_SUMMARY_PARSER_VERSION).toBeGreaterThanOrEqual(9)
+
+    const root = await createTempDir('coordinator-activity-cost-upgrade')
+    const configDir = join(root, 'config')
+    const databasePath = join(configDir, 'cc-haha', 'db', 'index-v1.sqlite')
+    const transcriptPath = join(configDir, 'projects', '-repo', 'cost-upgrade.jsonl')
+    await mkdir(dirname(transcriptPath), { recursive: true })
+    await writeFile(transcriptPath, [
+      {
+        type: 'user',
+        message: { role: 'user', content: 'Price this' },
+        timestamp: '2026-01-01T00:00:00.000Z',
+      },
+      {
+        type: 'assistant',
+        requestId: 'req_cost_upgrade',
+        message: {
+          id: 'msg_cost_upgrade',
+          role: 'assistant',
+          model: 'claude-sonnet-5',
+          content: [{ type: 'text', text: 'Priced' }],
+          usage: { input_tokens: 1_000_000, output_tokens: 1_000_000 },
+        },
+        timestamp: '2026-01-01T00:00:01.000Z',
+      },
+    ].map(entry => JSON.stringify(entry)).join('\n') + '\n')
+
+    const createIdleWatcher = (): ReconciliationWatcher => ({
+      async start() {},
+      async stop() {},
+      queueTranscriptPath() {},
+      queueFullSweep() {},
+      getMetrics: () => ({
+        queuedPaths: 0,
+        maxBatchSize: 0,
+        yielded: 0,
+        fullSweeps: 0,
+        watchFailures: 0,
+      }),
+    })
+    const previousCoordinator = createLocalIndexCoordinator({
+      resolveMode: () => ({ mode: 'on', warningCode: null }),
+      resolveScope: () => configDir,
+      resolveDatabasePath: () => databasePath,
+      createProjector: options => createSessionProjector({
+        ...options,
+        parserVersion: SESSION_SUMMARY_PARSER_VERSION - 1,
+      }),
+      createWatcher: createIdleWatcher,
+    })
+    await previousCoordinator.start()
+    await waitFor(() => previousCoordinator.isActivityScopeReady())
+    await previousCoordinator.stop()
+
+    // Leave behind what the previous release persisted: Sonnet 5 at the old $3/$15 rate.
+    const staleDatabase = new Database(databasePath)
+    try {
+      staleDatabase.run(
+        "UPDATE activity_daily_models SET cost_usd = 18 WHERE model = 'claude-sonnet-5'",
+      )
+      expect(staleDatabase.query<{ cost_usd: number }, []>(
+        "SELECT cost_usd FROM activity_daily_models WHERE model = 'claude-sonnet-5'",
+      ).get()?.cost_usd).toBe(18)
+    } finally {
+      staleDatabase.close()
+    }
+
+    let runScheduledDiscovery: (() => void) | undefined
+    const upgradedCoordinator = createLocalIndexCoordinator({
+      resolveMode: () => ({ mode: 'on', warningCode: null }),
+      resolveScope: () => configDir,
+      resolveDatabasePath: () => databasePath,
+      schedule: operation => { runScheduledDiscovery = operation },
+      createWatcher: createIdleWatcher,
+    })
+
+    try {
+      await upgradedCoordinator.start()
+      // The stale dollars are withheld until the rebuild has replaced them.
+      expect(upgradedCoordinator.getActivityStats('all')).toBeNull()
+
+      runScheduledDiscovery?.()
+      await waitFor(() => upgradedCoordinator.isActivityScopeReady())
+      // 1M input at $2 + 1M output at $10.
+      expect(upgradedCoordinator.getActivityStats('all')?.modelUsage['claude-sonnet-5']?.costUSD)
+        .toBeCloseTo(12, 6)
+    } finally {
+      await upgradedCoordinator.stop()
+    }
+  })
+
   it('keeps retained rows degraded after watch failure and ignores late batches after stop', async () => {
     const index = createFakeIndex([candidate(1)])
     let watcherOptions!: ReconciliationWatcherOptions
diff --git a/src/server/services/localIndex/sessionProjector.ts b/src/server/services/localIndex/sessionProjector.ts
index c9848816..df5f77c5 100644
--- a/src/server/services/localIndex/sessionProjector.ts
+++ b/src/server/services/localIndex/sessionProjector.ts
@@ -38,7 +38,9 @@ import type {
 // 6: protocol enforcement was removed; rebuild v5 summaries without protocol restrictions.
 // 7: independent desktop team workers remain addressable but leave sidebar listings.
 // 8: complete runtime selections clear the previous effort when no override is saved.
-export const SESSION_SUMMARY_PARSER_VERSION = 8
+// 9: usage cost rates were corrected (Sonnet 5, Sonnet 5.5, Opus 5.5, fast mode); rebuild the
+//    persisted per-model dollars.
+export const SESSION_SUMMARY_PARSER_VERSION = 9
 
 export type SessionSourceCandidate = {
   path: string
diff --git a/src/services/api/claudeRequiredThinking.test.ts b/src/services/api/claudeRequiredThinking.test.ts
index ec337def..7966f359 100644
--- a/src/services/api/claudeRequiredThinking.test.ts
+++ b/src/services/api/claudeRequiredThinking.test.ts
@@ -855,6 +855,26 @@ for (const disableAdaptive of [false, true]) {
   }, 10_000)
 }
 
+for (const disableAdaptive of [false, true]) {
+  test(`Sonnet 5.5 never sends disabled thinking, with optional adaptive disabled=${disableAdaptive}`, async () => {
+    const { content, requests } = await captureQueryRequest({
+      model: 'claude-sonnet-5-5',
+      configureCapabilityOverrides: false,
+      globalThinkingEnabled: false,
+      env: {
+        CLAUDE_CODE_DISABLE_ADAPTIVE_THINKING: disableAdaptive ? '1' : undefined,
+        CLAUDE_CODE_ALWAYS_ENABLE_EFFORT: '1',
+      },
+    })
+    expect(content).toContainEqual({ type: 'text', text: 'OK' })
+    expect(requests).toHaveLength(1)
+    expect(requests[0]?.model).toBe('claude-sonnet-5-5')
+    expect(requests[0]?.thinking).toEqual({ type: 'adaptive' })
+    expect(requests[0]?.max_tokens).toBe(128_000)
+    expect(requests[0]?.output_config).toEqual({ effort: 'medium' })
+  }, 10_000)
+}
+
 test('Opus 5.5 respects an explicit third-party capability opt-out', async () => {
   const { requests } = await captureQueryRequest({
     model: 'claude-opus-5-5',
diff --git a/src/skills/bundled/claudeApiContent.ts b/src/skills/bundled/claudeApiContent.ts
index 901cf3c8..3ade8abb 100644
--- a/src/skills/bundled/claudeApiContent.ts
+++ b/src/skills/bundled/claudeApiContent.ts
@@ -34,14 +34,14 @@ import typescriptClaudeApiToolUse from './claude-api/typescript/claude-api/tool-
 //   - claude-api/SKILL.md (Current Models pricing table)
 //   - claude-api/shared/models.md (full model catalog with legacy versions and alias mappings)
 export const SKILL_MODEL_VARS = {
-  OPUS_ID: 'claude-opus-4-8',
-  OPUS_NAME: 'Claude Opus 4.8',
-  SONNET_ID: 'claude-sonnet-5',
-  SONNET_NAME: 'Claude Sonnet 5',
+  OPUS_ID: 'claude-opus-5-5',
+  OPUS_NAME: 'Claude Opus 5.5',
+  SONNET_ID: 'claude-sonnet-5-5',
+  SONNET_NAME: 'Claude Sonnet 5.5',
   HAIKU_ID: 'claude-haiku-4-5',
   HAIKU_NAME: 'Claude Haiku 4.5',
   // Previous Sonnet ID — used in "do not append date suffixes" example in SKILL.md.
-  PREV_SONNET_ID: 'claude-sonnet-4-5',
+  PREV_SONNET_ID: 'claude-sonnet-5',
 } satisfies Record<string, string>
 
 export const SKILL_PROMPT: string = skillPrompt
diff --git a/src/utils/commitAttribution.ts b/src/utils/commitAttribution.ts
index 4857074f..f4f9eea8 100644
--- a/src/utils/commitAttribution.ts
+++ b/src/utils/commitAttribution.ts
@@ -162,6 +162,7 @@ export function sanitizeModelName(shortName: string): string {
   if (shortName.includes('opus-4-5')) return 'claude-opus-4-5'
   if (shortName.includes('opus-4-1')) return 'claude-opus-4-1'
   if (shortName.includes('opus-4')) return 'claude-opus-4'
+  if (shortName.includes('sonnet-5-5')) return 'claude-sonnet-5-5'
   if (shortName.includes('sonnet-5')) return 'claude-sonnet-5'
   if (shortName.includes('sonnet-4-6')) return 'claude-sonnet-4-6'
   if (shortName.includes('sonnet-4-5')) return 'claude-sonnet-4-5'
diff --git a/src/utils/context.ts b/src/utils/context.ts
index c34e0732..7698396d 100644
--- a/src/utils/context.ts
+++ b/src/utils/context.ts
@@ -269,7 +269,7 @@ export function getModelMaxOutputTokens(model: string): {
 
   const m = getCanonicalName(model)
 
-  if (m === 'claude-opus-5-5') {
+  if (m === 'claude-opus-5-5' || m === 'claude-sonnet-5-5') {
     defaultTokens = 128_000
     upperLimit = 128_000
   } else if (
diff --git a/src/utils/effort.ts b/src/utils/effort.ts
index 0b92abde..ed2f75f8 100644
--- a/src/utils/effort.ts
+++ b/src/utils/effort.ts
@@ -435,7 +435,10 @@ export function getDefaultEffortForModel(
   // the model launch DRI and research. Default effort is a sensitive setting
   // that can greatly affect model quality and bashing.
 
-  if (getCanonicalName(model) === 'claude-opus-5-5') {
+  // Claude Code runs Opus 5.5 and Sonnet 5.5 at medium; the API default for
+  // Sonnet 5.5 is high, so it must be sent explicitly.
+  const canonicalModel = getCanonicalName(model)
+  if (canonicalModel === 'claude-opus-5-5' || canonicalModel === 'claude-sonnet-5-5') {
     return 'medium'
   }
 
diff --git a/src/utils/model/configs.ts b/src/utils/model/configs.ts
index 0895d68c..9948c9d7 100644
--- a/src/utils/model/configs.ts
+++ b/src/utils/model/configs.ts
@@ -62,6 +62,14 @@ export const CLAUDE_SONNET_5_CONFIG = {
   azureOpenAI: 'claude-sonnet-5',
 } as const satisfies ModelConfig
 
+export const CLAUDE_SONNET_5_5_CONFIG = {
+  firstParty: 'claude-sonnet-5-5',
+  bedrock: 'us.anthropic.claude-sonnet-5-5',
+  vertex: 'claude-sonnet-5-5',
+  foundry: 'claude-sonnet-5-5',
+  azureOpenAI: 'claude-sonnet-5-5',
+} as const satisfies ModelConfig
+
 export const CLAUDE_SONNET_4_CONFIG = {
   firstParty: 'claude-sonnet-4-20250514',
   bedrock: 'us.anthropic.claude-sonnet-4-20250514-v1:0',
@@ -178,6 +186,7 @@ export const ALL_MODEL_CONFIGS = {
   sonnet45: CLAUDE_SONNET_4_5_CONFIG,
   sonnet46: CLAUDE_SONNET_4_6_CONFIG,
   sonnet50: CLAUDE_SONNET_5_CONFIG,
+  sonnet55: CLAUDE_SONNET_5_5_CONFIG,
   opus40: CLAUDE_OPUS_4_CONFIG,
   opus41: CLAUDE_OPUS_4_1_CONFIG,
   opus45: CLAUDE_OPUS_4_5_CONFIG,
diff --git a/src/utils/model/fable.test.ts b/src/utils/model/fable.test.ts
index 8c10711a..d3c3eb71 100644
--- a/src/utils/model/fable.test.ts
+++ b/src/utils/model/fable.test.ts
@@ -129,7 +129,7 @@ describe('Fable model configuration', () => {
     expect(getMarketingNameForModel('claude-opus-4-8')).toBe('Opus 4.8')
     expect(getMarketingNameForModel('claude-sonnet-5')).toBe('Sonnet 5')
     expect(renderDefaultModelSetting('opusplan')).toBe(
-      'Opus 5 in plan mode, else Sonnet 5',
+      'Opus 5.5 in plan mode, else Sonnet 5.5',
     )
   })
 
@@ -158,24 +158,48 @@ describe('Fable model configuration', () => {
     })
   })
 
-  test('publishes current model IDs and knowledge cutoffs in environment context', async () => {
+  test('publishes the current model lineup in environment context', async () => {
     expect(SKILL_MODEL_VARS).toMatchObject({
-      OPUS_ID: 'claude-opus-4-8',
-      OPUS_NAME: 'Claude Opus 4.8',
-      SONNET_ID: 'claude-sonnet-5',
-      SONNET_NAME: 'Claude Sonnet 5',
+      OPUS_ID: 'claude-opus-5-5',
+      OPUS_NAME: 'Claude Opus 5.5',
+      SONNET_ID: 'claude-sonnet-5-5',
+      SONNET_NAME: 'Claude Sonnet 5.5',
+      PREV_SONNET_ID: 'claude-sonnet-5',
     })
 
-    for (const model of ['claude-fable-5', 'claude-opus-4-8', 'claude-sonnet-5']) {
+    for (const model of ['claude-fable-5', 'claude-opus-4-8', 'claude-sonnet-5', 'claude-sonnet-5-5']) {
       const info = await computeSimpleEnvInfo(model)
-      expect(info).toContain('Assistant knowledge cutoff is January 2026.')
-      expect(info).toContain("Fable 5: 'claude-fable-5'")
-      expect(info).toContain("Opus 4.8: 'claude-opus-4-8'")
-      expect(info).toContain("Sonnet 5: 'claude-sonnet-5'")
-      expect(info).toContain('same Claude Opus 4.8 model')
+      expect(info).toContain('The most recent Claude models are the Claude 5 family and Haiku 4.5.')
+      expect(info).toContain("Fable 5.1: 'claude-fable-5-1'")
+      expect(info).toContain("Opus 5.5: 'claude-opus-5-5'")
+      expect(info).toContain("Sonnet 5.5: 'claude-sonnet-5-5'")
+      expect(info).toContain("Haiku 4.5: 'claude-haiku-4-5-20251001'")
+      // The fast-mode note no longer names an Opus generation that has since been superseded.
+      expect(info).toContain('Fast mode for Claude Code uses Claude Opus with faster output')
+      expect(info).not.toContain('same Claude Opus 4.8 model')
     }
   })
 
+  // Reliable knowledge cutoffs: https://platform.claude.com/docs/en/models/overview and each
+  // model's page, which match the official Claude Code model catalog.
+  test.each([
+    ['claude-fable-5-1', 'June 2026'],
+    ['claude-opus-5-5', 'June 2026'],
+    ['claude-sonnet-5-5', 'June 2026'],
+    ['claude-opus-5', 'May 2026'],
+    ['claude-fable-5', 'January 2026'],
+    ['claude-opus-4-8', 'January 2026'],
+    ['claude-opus-4-7', 'January 2026'],
+    ['claude-sonnet-5', 'January 2026'],
+    ['claude-sonnet-4-6', 'August 2025'],
+    ['claude-opus-4-5', 'May 2025'],
+    ['claude-haiku-4-5', 'February 2025'],
+  ])('tells %s its knowledge cutoff is %s', async (model, cutoff) => {
+    expect(await computeSimpleEnvInfo(model)).toContain(`Assistant knowledge cutoff is ${cutoff}.`)
+    // A context-window marker does not change what the model knows.
+    expect(await computeSimpleEnvInfo(`${model}[1m]`)).toContain(`Assistant knowledge cutoff is ${cutoff}.`)
+  })
+
   test('sanitizes new model trailers and keeps teammate fallbacks provider-safe', () => {
     expect(sanitizeModelName('claude-fable-5-1-experimental')).toBe('claude-fable-5-1')
     expect(sanitizeModelName('claude-fable-5-experimental')).toBe('claude-fable-5')
diff --git a/src/utils/model/model.ts b/src/utils/model/model.ts
index 90c8ffb4..fed3d9c9 100644
--- a/src/utils/model/model.ts
+++ b/src/utils/model/model.ts
@@ -22,7 +22,11 @@ import {
 } from '../context.js'
 import { isEnvTruthy } from '../envUtils.js'
 import { getModelStrings, resolveOverriddenModel } from './modelStrings.js'
-import { formatModelPricing, getOpus46CostTier } from '../modelCost.js'
+import {
+  formatModelPricing,
+  getModelPricingString,
+  getOpus46CostTier,
+} from '../modelCost.js'
 import { getSettings_DEPRECATED } from '../settings/settings.js'
 import type { PermissionMode } from '../permissions/PermissionMode.js'
 import {
@@ -144,7 +148,7 @@ export function getDefaultOpusModel(): ModelName {
   if (shouldUseThirdPartyAnthropicModelDefaults()) {
     return getModelStrings().opus46
   }
-  return getModelStrings().opus50
+  return getModelStrings().opus55
 }
 
 // @[MODEL LAUNCH]: Update the default Sonnet model (3P providers may lag so keep defaults unchanged).
@@ -159,7 +163,7 @@ export function getDefaultSonnetModel(): ModelName {
   if (shouldUseThirdPartyAnthropicModelDefaults()) {
     return getModelStrings().sonnet45
   }
-  return getModelStrings().sonnet50
+  return getModelStrings().sonnet55
 }
 
 // @[MODEL LAUNCH]: Update the default Haiku model (3P providers may lag so keep defaults unchanged).
@@ -296,6 +300,9 @@ export function firstPartyNameToCanonical(name: ModelName): ModelShortName {
   if (name.includes('claude-opus-4')) {
     return 'claude-opus-4'
   }
+  if (name.includes('claude-sonnet-5-5')) {
+    return 'claude-sonnet-5-5'
+  }
   if (name.includes('claude-sonnet-5')) {
     return 'claude-sonnet-5'
   }
@@ -363,11 +370,11 @@ export function getClaudeAiUserDefaultModelDescription(
   }
   if (isMaxSubscriber() || isTeamPremiumSubscriber()) {
     if (isOpus1mMergeEnabled()) {
-      return `Opus 5 with 1M context · Most capable for complex work${fastMode ? getOpus46PricingSuffix(true) : ''}`
+      return `Opus 5.5 with 1M context · Most capable for complex work${fastMode ? getOpus46PricingSuffix(true) : ''}`
     }
-    return `Opus 5 · Most capable for complex work${fastMode ? getOpus46PricingSuffix(true) : ''}`
+    return `Opus 5.5 · Most capable for complex work${fastMode ? getOpus46PricingSuffix(true) : ''}`
   }
-  return 'Sonnet 5 · Best for everyday tasks'
+  return 'Sonnet 5.5 · Best for everyday tasks'
 }
 
 export function renderDefaultModelSetting(
@@ -381,7 +388,12 @@ export function renderDefaultModelSetting(
 
 export function getOpus46PricingSuffix(fastMode: boolean): string {
   if (getAPIProvider() !== 'firstParty') return ''
-  const pricing = formatModelPricing(getOpus46CostTier(fastMode))
+  // Standard rates follow whichever Opus the `opus` alias resolves to; only the fast-mode
+  // premium is still the tier published for Opus 4.7.
+  const pricing = fastMode
+    ? formatModelPricing(getOpus46CostTier(true))
+    : (getModelPricingString(getDefaultOpusModel()) ??
+      formatModelPricing(getOpus46CostTier(false)))
   const fastModeIndicator = fastMode ? ` (${LIGHTNING_BOLT})` : ''
   return ` ·${fastModeIndicator} ${pricing}`
 }
@@ -461,6 +473,10 @@ export function getPublicModelDisplayName(model: ModelName): string | null {
       return 'Sonnet 4.6 (1M context)'
     case getModelStrings().sonnet46:
       return 'Sonnet 4.6'
+    case getModelStrings().sonnet55 + '[1m]':
+      return 'Sonnet 5.5 (1M context)'
+    case getModelStrings().sonnet55:
+      return 'Sonnet 5.5'
     case getModelStrings().sonnet50 + '[1m]':
       return 'Sonnet 5 (1M context)'
     case getModelStrings().sonnet50:
@@ -712,6 +728,9 @@ export function getMarketingNameForModel(modelId: string): string | undefined {
   if (canonical.includes('claude-opus-4')) {
     return 'Opus 4'
   }
+  if (canonical.includes('claude-sonnet-5-5')) {
+    return has1m ? 'Sonnet 5.5 (with 1M context)' : 'Sonnet 5.5'
+  }
   if (canonical.includes('claude-sonnet-5')) {
     return has1m ? 'Sonnet 5 (with 1M context)' : 'Sonnet 5'
   }
diff --git a/src/utils/model/modelContextWindows.ts b/src/utils/model/modelContextWindows.ts
index 69d888b5..10938e56 100644
--- a/src/utils/model/modelContextWindows.ts
+++ b/src/utils/model/modelContextWindows.ts
@@ -9,6 +9,7 @@ const DIRECT_MODEL_CONTEXT_WINDOWS: Record<string, number> = {
   'claude-opus-5': 1_000_000,
   'claude-opus-4-8': 1_000_000,
   'claude-opus-4-7': 1_000_000,
+  'claude-sonnet-5-5': 1_000_000,
   'claude-sonnet-5': 1_000_000,
   'claude-sonnet-4-6': 200_000,
   'claude-haiku-4-5': 200_000,
diff --git a/src/utils/model/modelOptions.ts b/src/utils/model/modelOptions.ts
index b7b6490f..48d199ae 100644
--- a/src/utils/model/modelOptions.ts
+++ b/src/utils/model/modelOptions.ts
@@ -10,7 +10,7 @@ import {
 import { getModelStrings } from './modelStrings.js'
 import {
   COST_TIER_10_50,
-  COST_TIER_3_15,
+  COST_TIER_2_10,
   COST_HAIKU_35,
   COST_HAIKU_45,
   formatModelPricing,
@@ -122,7 +122,7 @@ export function getDefaultOptionForUser(fastMode = false): ModelOption {
       ? ''
       : currentModel.includes('Opus')
         ? getOpus46PricingSuffix(fastMode)
-        : ` · ${formatModelPricing(COST_TIER_3_15)}`
+        : ` · ${formatModelPricing(COST_TIER_2_10)}`
   return {
     value: null,
     label: 'Default (recommended)',
@@ -182,11 +182,11 @@ function getFable5Option(): ModelOption | undefined {
 
 function getSonnet46Option(): ModelOption {
   const is3P = shouldUseThirdPartyAnthropicOptions()
-  const modelName = is3P ? 'Sonnet 4.6' : 'Sonnet 5'
+  const modelName = is3P ? 'Sonnet 4.6' : 'Sonnet 5.5'
   return {
     value: is3P ? getModelStrings().sonnet46 : 'sonnet',
     label: 'Sonnet',
-    description: `${modelName} · Best for everyday tasks${is3P ? '' : ` · ${formatModelPricing(COST_TIER_3_15)}`}`,
+    description: `${modelName} · Best for everyday tasks${is3P ? '' : ` · ${formatModelPricing(COST_TIER_2_10)}`}`,
     descriptionForModel:
       `${modelName} - best for everyday tasks. Generally recommended for most coding tasks`,
   }
@@ -223,18 +223,18 @@ function getOpus46Option(fastMode = false): ModelOption {
   return {
     value: is3P ? getModelStrings().opus46 : 'opus',
     label: 'Opus',
-    description: `${is3P ? 'Opus 4.7' : 'Opus 5'} · Most capable for complex work${getOpus46PricingSuffix(fastMode)}`,
-    descriptionForModel: `${is3P ? 'Opus 4.7' : 'Opus 5'} - most capable for complex work`,
+    description: `${is3P ? 'Opus 4.7' : 'Opus 5.5'} · Most capable for complex work${getOpus46PricingSuffix(fastMode)}`,
+    descriptionForModel: `${is3P ? 'Opus 4.7' : 'Opus 5.5'} - most capable for complex work`,
   }
 }
 
 export function getSonnet46_1MOption(): ModelOption {
   const is3P = shouldUseThirdPartyAnthropicOptions()
-  const modelName = is3P ? 'Sonnet 4.6' : 'Sonnet 5'
+  const modelName = is3P ? 'Sonnet 4.6' : 'Sonnet 5.5'
   return {
     value: is3P ? getModelStrings().sonnet46 + '[1m]' : 'sonnet[1m]',
     label: 'Sonnet (1M context)',
-    description: `${modelName} for long sessions${is3P ? '' : ` · ${formatModelPricing(COST_TIER_3_15)}`}`,
+    description: `${modelName} for long sessions${is3P ? '' : ` · ${formatModelPricing(COST_TIER_2_10)}`}`,
     descriptionForModel:
       `${modelName} with 1M context window - for long sessions with large codebases`,
   }
@@ -242,7 +242,7 @@ export function getSonnet46_1MOption(): ModelOption {
 
 export function getOpus46_1MOption(fastMode = false): ModelOption {
   const is3P = shouldUseThirdPartyAnthropicOptions()
-  const modelName = is3P ? 'Opus 4.7' : 'Opus 5'
+  const modelName = is3P ? 'Opus 4.7' : 'Opus 5.5'
   return {
     value: is3P ? getModelStrings().opus46 + '[1m]' : 'opus[1m]',
     label: 'Opus (1M context)',
@@ -302,7 +302,7 @@ function getMaxOpusOption(fastMode = false): ModelOption {
   return {
     value: 'opus',
     label: 'Opus',
-    description: `Opus 5 · Most capable for complex work${fastMode ? getOpus46PricingSuffix(true) : ''}`,
+    description: `Opus 5.5 · Most capable for complex work${fastMode ? getOpus46PricingSuffix(true) : ''}`,
   }
 }
 
@@ -312,7 +312,7 @@ export function getMaxSonnet46_1MOption(): ModelOption {
   return {
     value: 'sonnet[1m]',
     label: 'Sonnet (1M context)',
-    description: `Sonnet 5 with 1M context${billingInfo}${is3P ? '' : ` · ${formatModelPricing(COST_TIER_3_15)}`}`,
+    description: `Sonnet 5.5 with 1M context${billingInfo}${is3P ? '' : ` · ${formatModelPricing(COST_TIER_2_10)}`}`,
   }
 }
 
@@ -321,7 +321,7 @@ export function getMaxOpus46_1MOption(fastMode = false): ModelOption {
   return {
     value: 'opus[1m]',
     label: 'Opus (1M context)',
-    description: `Opus 5 with 1M context${billingInfo}${getOpus46PricingSuffix(fastMode)}`,
+    description: `Opus 5.5 with 1M context${billingInfo}${getOpus46PricingSuffix(fastMode)}`,
   }
 }
 
@@ -330,16 +330,16 @@ function getMergedOpus1MOption(fastMode = false): ModelOption {
   return {
     value: is3P ? getModelStrings().opus46 + '[1m]' : 'opus[1m]',
     label: 'Opus (1M context)',
-    description: `${is3P ? 'Opus 4.7' : 'Opus 5'} with 1M context · Most capable for complex work${!is3P && fastMode ? getOpus46PricingSuffix(fastMode) : ''}`,
+    description: `${is3P ? 'Opus 4.7' : 'Opus 5.5'} with 1M context · Most capable for complex work${!is3P && fastMode ? getOpus46PricingSuffix(fastMode) : ''}`,
     descriptionForModel:
-      `${is3P ? 'Opus 4.7' : 'Opus 5'} with 1M context - most capable for complex work`,
+      `${is3P ? 'Opus 4.7' : 'Opus 5.5'} with 1M context - most capable for complex work`,
   }
 }
 
 const MaxSonnet46Option: ModelOption = {
   value: 'sonnet',
   label: 'Sonnet',
-  description: 'Sonnet 5 · Best for everyday tasks',
+  description: 'Sonnet 5.5 · Best for everyday tasks',
 }
 
 const MaxHaiku45Option: ModelOption = {
@@ -476,8 +476,8 @@ function getModelOptionsBase(fastMode = false): ModelOption[] {
     return standardOptions
   }
 
-  // PAYG 1P API: Default (Opus 5) + Fable + Sonnet + Haiku.
-  // Opus 5 and Sonnet 5 already have native 1M context windows.
+  // PAYG 1P API: Default (Opus 5.5) + Fable + Sonnet + Haiku.
+  // Opus 5.x and Sonnet 5.x already have native 1M context windows.
   if (!shouldUseThirdPartyAnthropicOptions()) {
     const payg1POptions = [getDefaultOptionForUser(fastMode)]
     pushUniqueOption(payg1POptions, getFable5Option())
@@ -569,8 +569,13 @@ function getModelFamilyInfo(
     }
   }
 
-  // Opus family
-  if (canonical.includes('claude-opus-4')) {
+  // Opus family. A pinned Opus 5 only has a newer alias target where the alias has moved
+  // on to Opus 5.5; third-party defaults lag on Opus 4.7, which is not an upgrade.
+  if (
+    canonical.includes('claude-opus-4') ||
+    (canonical === 'claude-opus-5' &&
+      getCanonicalName(getDefaultOpusModel()) === 'claude-opus-5-5')
+  ) {
     const currentName = getMarketingNameForModel(getDefaultOpusModel())
     if (currentName) {
       return { alias: 'Opus', currentVersionName: currentName }
diff --git a/src/utils/model/opus5.test.ts b/src/utils/model/opus5.test.ts
index 80d033e2..f80539d7 100644
--- a/src/utils/model/opus5.test.ts
+++ b/src/utils/model/opus5.test.ts
@@ -6,11 +6,16 @@ import { clearOAuthTokenCache } from '../auth.js'
 import { resetSettingsCache } from '../settings/settingsCache.js'
 import { sanitizeModelName } from '../commitAttribution.js'
 import { ALL_MODEL_CONFIGS } from './configs.js'
-import { getOpus46_1MOption, getMaxOpus46_1MOption } from './modelOptions.js'
+import {
+  getModelOptions,
+  getOpus46_1MOption,
+  getMaxOpus46_1MOption,
+} from './modelOptions.js'
 import {
   firstPartyNameToCanonical,
   getDefaultOpusModel,
   getMarketingNameForModel,
+  getOpus46PricingSuffix,
   getPublicModelDisplayName,
   isNonCustomOpusModel,
   parseUserSpecifiedModel,
@@ -22,6 +27,7 @@ const envKeys = [
   'CLAUDE_CONFIG_DIR',
   'ANTHROPIC_BASE_URL',
   'ANTHROPIC_API_KEY',
+  'ANTHROPIC_MODEL',
   'ANTHROPIC_DEFAULT_OPUS_MODEL',
   'CLAUDE_CODE_USE_BEDROCK',
   'CLAUDE_CODE_USE_VERTEX',
@@ -52,13 +58,15 @@ afterEach(() => {
 })
 
 describe('Opus 5 runtime model identity', () => {
-  test('registers and resolves the latest official Opus without rewriting pinned models', () => {
+  test('registers Opus 5 and leaves a pinned Opus 5 alone now that the opus alias tracks Opus 5.5', () => {
     expect(Object.values(ALL_MODEL_CONFIGS).some(config => config.firstParty === 'claude-opus-5')).toBe(true)
-    expect(getDefaultOpusModel()).toBe('claude-opus-5')
-    expect(parseUserSpecifiedModel('opus')).toBe('claude-opus-5')
-    expect(parseUserSpecifiedModel('opus[1m]')).toBe('claude-opus-5[1m]')
+    expect(getDefaultOpusModel()).toBe('claude-opus-5-5')
+    expect(parseUserSpecifiedModel('opus')).toBe('claude-opus-5-5')
+    expect(parseUserSpecifiedModel('opus[1m]')).toBe('claude-opus-5-5[1m]')
+    expect(parseUserSpecifiedModel('claude-opus-5')).toBe('claude-opus-5')
+    expect(parseUserSpecifiedModel('claude-opus-5[1m]')).toBe('claude-opus-5[1m]')
     expect(parseUserSpecifiedModel('claude-opus-4-8')).toBe('claude-opus-4-8')
-    expect(renderDefaultModelSetting('opusplan')).toBe('Opus 5 in plan mode, else Sonnet 5')
+    expect(renderDefaultModelSetting('opusplan')).toBe('Opus 5.5 in plan mode, else Sonnet 5.5')
   })
 
   test('preserves explicit provider overrides and third-party defaults', () => {
@@ -70,13 +78,52 @@ describe('Opus 5 runtime model identity', () => {
   })
 
   test('describes the Opus alias with its actual resolved generation', () => {
-    expect(getOpus46_1MOption().description).toContain('Opus 5')
-    expect(getMaxOpus46_1MOption().description).toContain('Opus 5')
+    expect(getOpus46_1MOption().description).toContain('Opus 5.5')
+    expect(getMaxOpus46_1MOption().description).toContain('Opus 5.5')
     process.env.ANTHROPIC_BASE_URL = 'https://provider.example.invalid'
     process.env.ANTHROPIC_API_KEY = 'fixture-key'
     expect(getOpus46_1MOption().description).toContain('Opus 4.7')
   })
 
+  test('quotes the price of the Opus the alias resolves to', () => {
+    // Opus 5.5 is $4/$20; quoting the $5/$25 of Opus 5 or 4.7 would overstate it.
+    expect(getOpus46PricingSuffix(false)).toBe(' · $4/$20 per Mtok')
+
+    process.env.ANTHROPIC_BASE_URL = 'https://provider.example.invalid'
+    process.env.ANTHROPIC_API_KEY = 'fixture-key'
+    // The lag-safe third-party default is Opus 4.7 ($5/$25).
+    expect(getOpus46PricingSuffix(false)).toBe(' · $5/$25 per Mtok')
+
+    process.env.CLAUDE_CODE_USE_BEDROCK = '1'
+    expect(getOpus46PricingSuffix(false)).toBe('')
+  })
+
+  test('hints that a pinned Opus 5 has a newer alias target only where the alias moved to Opus 5.5', () => {
+    process.env.ANTHROPIC_API_KEY = 'fixture-key'
+    process.env.ANTHROPIC_MODEL = 'claude-opus-5'
+    expect(getModelOptions()).toContainEqual({
+      value: 'claude-opus-5',
+      label: 'Opus 5',
+      description: 'Newer version available · select Opus for Opus 5.5',
+    })
+
+    process.env.ANTHROPIC_MODEL = 'claude-opus-5-5'
+    expect(getModelOptions()).toContainEqual({
+      value: 'claude-opus-5-5',
+      label: 'Opus 5.5',
+      description: 'claude-opus-5-5',
+    })
+
+    // Third-party defaults lag on Opus 4.7, which is not an upgrade over a pinned Opus 5.
+    process.env.ANTHROPIC_BASE_URL = 'https://provider.example.invalid'
+    process.env.ANTHROPIC_MODEL = 'claude-opus-5'
+    expect(getModelOptions()).toContainEqual({
+      value: 'claude-opus-5',
+      label: 'Opus 5',
+      description: 'claude-opus-5',
+    })
+  })
+
   test('recognizes Opus 5 throughout canonicalization, public display, and attribution', () => {
     expect(firstPartyNameToCanonical('anthropic.claude-opus-5')).toBe('claude-opus-5')
     expect(isNonCustomOpusModel('claude-opus-5')).toBe(true)
diff --git a/src/utils/model/sonnet55.test.ts b/src/utils/model/sonnet55.test.ts
new file mode 100644
index 00000000..a6ecaf8e
--- /dev/null
+++ b/src/utils/model/sonnet55.test.ts
@@ -0,0 +1,256 @@
+import { afterEach, beforeEach, describe, expect, test } from 'bun:test'
+import { mkdtempSync, rmSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { computeSimpleEnvInfo } from '../../constants/prompts.js'
+import { clearOAuthTokenCache } from '../auth.js'
+import { sanitizeModelName } from '../commitAttribution.js'
+import {
+  getContextWindowForModel,
+  getModelMaxOutputTokens,
+  modelSupports1M,
+} from '../context.js'
+import {
+  getDefaultEffortForModel,
+  modelSupportsEffort,
+  modelSupportsMaxEffort,
+  modelSupportsXHighEffort,
+} from '../effort.js'
+import { calculateCostFromTokens, getModelPricingString } from '../modelCost.js'
+import { resetSettingsCache } from '../settings/settingsCache.js'
+import { resolveSideQueryThinkingConfig } from '../sideQuery.js'
+import {
+  modelRequiresThinking,
+  modelSupportsAdaptiveThinking,
+  modelSupportsThinking,
+  modelUsesBoundThinking,
+} from '../thinking.js'
+import { resolveModelCosts } from '../usageAccounting.js'
+import { ALL_MODEL_CONFIGS } from './configs.js'
+import {
+  firstPartyNameToCanonical,
+  getClaudeAiUserDefaultModelDescription,
+  getDefaultSonnetModel,
+  getMarketingNameForModel,
+  getPublicModelDisplayName,
+  parseUserSpecifiedModel,
+  renderDefaultModelSetting,
+} from './model.js'
+import { getMaxSonnet46_1MOption, getSonnet46_1MOption } from './modelOptions.js'
+import { get3PModelCapabilityOverride } from './modelSupportOverrides.js'
+
+const envKeys = [
+  'HOME',
+  'CLAUDE_CONFIG_DIR',
+  'ANTHROPIC_BASE_URL',
+  'ANTHROPIC_API_KEY',
+  'ANTHROPIC_MODEL',
+  'ANTHROPIC_DEFAULT_SONNET_MODEL',
+  'ANTHROPIC_DEFAULT_SONNET_MODEL_SUPPORTED_CAPABILITIES',
+  'CLAUDE_CODE_USE_BEDROCK',
+  'CLAUDE_CODE_USE_VERTEX',
+  'CLAUDE_CODE_USE_FOUNDRY',
+  'CLAUDE_CODE_DISABLE_1M_CONTEXT',
+  'CLAUDE_CODE_DISABLE_ADAPTIVE_THINKING',
+  'CC_HAHA_SEND_DISABLED_THINKING',
+] as const
+let savedEnv: (string | undefined)[]
+let temporaryHome: string
+
+function clearCapabilityCache() {
+  ;(get3PModelCapabilityOverride as typeof get3PModelCapabilityOverride & {
+    cache?: { clear?: () => void }
+  }).cache?.clear?.()
+}
+
+beforeEach(() => {
+  savedEnv = envKeys.map(key => process.env[key])
+  for (const key of envKeys) delete process.env[key]
+  temporaryHome = mkdtempSync(join(tmpdir(), 'sonnet55-model-test-'))
+  process.env.HOME = temporaryHome
+  process.env.CLAUDE_CONFIG_DIR = join(temporaryHome, 'config')
+  resetSettingsCache()
+  clearOAuthTokenCache()
+  clearCapabilityCache()
+})
+
+afterEach(() => {
+  resetSettingsCache()
+  clearOAuthTokenCache()
+  clearCapabilityCache()
+  rmSync(temporaryHome, { recursive: true, force: true })
+  envKeys.forEach((key, index) => {
+    const value = savedEnv[index]
+    if (value === undefined) delete process.env[key]
+    else process.env[key] = value
+  })
+})
+
+const SONNET_55_VARIANTS = [
+  'claude-sonnet-5-5',
+  'claude-sonnet-5-5[1m]',
+  'us.anthropic.claude-sonnet-5-5',
+  'anthropic.claude-sonnet-5-5',
+]
+
+describe('Sonnet 5.5 identity', () => {
+  test('registers the official IDs without absorbing the Sonnet 5 it supersedes', () => {
+    expect(ALL_MODEL_CONFIGS.sonnet55).toMatchObject({
+      firstParty: 'claude-sonnet-5-5',
+      vertex: 'claude-sonnet-5-5',
+      foundry: 'claude-sonnet-5-5',
+    })
+    expect(ALL_MODEL_CONFIGS.sonnet55.bedrock).toMatch(/anthropic\.claude-sonnet-5-5$/)
+
+    for (const model of SONNET_55_VARIANTS) {
+      expect(firstPartyNameToCanonical(model)).toBe('claude-sonnet-5-5')
+      expect(sanitizeModelName(model)).toBe('claude-sonnet-5-5')
+    }
+    // `claude-sonnet-5` is a prefix of `claude-sonnet-5-5`; each keeps its own identity.
+    for (const model of ['claude-sonnet-5', 'anthropic.claude-sonnet-5']) {
+      expect(firstPartyNameToCanonical(model)).toBe('claude-sonnet-5')
+      expect(sanitizeModelName(model)).toBe('claude-sonnet-5')
+    }
+  })
+
+  test('renders distinct public and marketing names', () => {
+    expect(getPublicModelDisplayName('claude-sonnet-5-5')).toBe('Sonnet 5.5')
+    expect(getPublicModelDisplayName('claude-sonnet-5-5[1m]')).toBe('Sonnet 5.5 (1M context)')
+    expect(getMarketingNameForModel('claude-sonnet-5-5')).toBe('Sonnet 5.5')
+    expect(getMarketingNameForModel('claude-sonnet-5-5[1m]')).toBe('Sonnet 5.5 (with 1M context)')
+    expect(getPublicModelDisplayName('claude-sonnet-5')).toBe('Sonnet 5')
+    expect(getMarketingNameForModel('claude-sonnet-5')).toBe('Sonnet 5')
+  })
+
+  test('tells the model its own name, ID and June 2026 knowledge cutoff', async () => {
+    const info = await computeSimpleEnvInfo('claude-sonnet-5-5')
+    expect(info).toContain(
+      'You are powered by the model named Sonnet 5.5. The exact model ID is claude-sonnet-5-5.',
+    )
+    expect(info).toContain('Assistant knowledge cutoff is June 2026.')
+  })
+})
+
+describe('Sonnet alias resolution', () => {
+  test('resolves the sonnet alias to Sonnet 5.5 and keeps explicit pins untouched', () => {
+    expect(getDefaultSonnetModel()).toBe('claude-sonnet-5-5')
+    expect(parseUserSpecifiedModel('sonnet')).toBe('claude-sonnet-5-5')
+    expect(parseUserSpecifiedModel('sonnet[1m]')).toBe('claude-sonnet-5-5[1m]')
+    expect(parseUserSpecifiedModel('claude-sonnet-5')).toBe('claude-sonnet-5')
+    expect(parseUserSpecifiedModel('claude-sonnet-5-5')).toBe('claude-sonnet-5-5')
+    expect(renderDefaultModelSetting('opusplan')).toBe('Opus 5.5 in plan mode, else Sonnet 5.5')
+  })
+
+  test('keeps lag-safe third-party defaults and honors provider overrides', () => {
+    process.env.ANTHROPIC_BASE_URL = 'https://provider.example.invalid'
+    process.env.ANTHROPIC_API_KEY = 'fixture-key'
+    expect(getDefaultSonnetModel()).toBe('claude-sonnet-4-5-20250929')
+    process.env.ANTHROPIC_DEFAULT_SONNET_MODEL = 'provider-custom-sonnet'
+    expect(parseUserSpecifiedModel('sonnet')).toBe('provider-custom-sonnet')
+  })
+
+  test('describes the alias with its actual resolved generation and price', () => {
+    expect(getClaudeAiUserDefaultModelDescription()).toBe('Sonnet 5.5 · Best for everyday tasks')
+    expect(getSonnet46_1MOption().description).toBe('Sonnet 5.5 for long sessions · $2/$10 per Mtok')
+    expect(getMaxSonnet46_1MOption().description).toBe('Sonnet 5.5 with 1M context · $2/$10 per Mtok')
+
+    process.env.ANTHROPIC_BASE_URL = 'https://provider.example.invalid'
+    process.env.ANTHROPIC_API_KEY = 'fixture-key'
+    expect(getSonnet46_1MOption().description).toBe('Sonnet 4.6 for long sessions')
+  })
+})
+
+describe('Sonnet 5.5 runtime limits and thinking', () => {
+  test('exposes the native 1M window and the 128K output limit', () => {
+    for (const model of SONNET_55_VARIANTS) {
+      expect(modelSupports1M(model)).toBe(true)
+    }
+    expect(getContextWindowForModel('claude-sonnet-5-5')).toBe(1_000_000)
+    expect(getContextWindowForModel('claude-sonnet-5-5[1m]')).toBe(1_000_000)
+    expect(getModelMaxOutputTokens('claude-sonnet-5-5')).toEqual({
+      default: 128_000,
+      upperLimit: 128_000,
+    })
+    expect(getModelMaxOutputTokens('claude-sonnet-5')).toEqual({
+      default: 64_000,
+      upperLimit: 128_000,
+    })
+  })
+
+  test('always runs adaptive thinking because the API rejects thinking: disabled', () => {
+    for (const model of SONNET_55_VARIANTS) {
+      expect(modelSupportsThinking(model)).toBe(true)
+      expect(modelSupportsAdaptiveThinking(model)).toBe(true)
+      expect(modelRequiresThinking(model)).toBe(true)
+    }
+    expect(modelUsesBoundThinking('claude-sonnet-5-5')).toBe(false)
+    // Sonnet 5 still accepts an explicit disable.
+    expect(modelRequiresThinking('claude-sonnet-5')).toBe(false)
+  })
+
+  test('never lets a side query send disabled thinking to Sonnet 5.5', () => {
+    expect(resolveSideQueryThinkingConfig(false, 1024, 'claude-sonnet-5-5')).toEqual({
+      type: 'adaptive',
+    })
+    expect(resolveSideQueryThinkingConfig(undefined, 1024, 'claude-sonnet-5-5[1m]')).toEqual({
+      type: 'adaptive',
+    })
+    expect(resolveSideQueryThinkingConfig(false, 1024, 'claude-sonnet-5')).toEqual({
+      type: 'disabled',
+    })
+  })
+
+  test('respects an explicit third-party capability opt-out', () => {
+    process.env.ANTHROPIC_BASE_URL = 'https://provider.example.invalid'
+    process.env.ANTHROPIC_API_KEY = 'fixture-key'
+    process.env.ANTHROPIC_DEFAULT_SONNET_MODEL = 'claude-sonnet-5-5'
+    process.env.ANTHROPIC_DEFAULT_SONNET_MODEL_SUPPORTED_CAPABILITIES = ''
+    clearCapabilityCache()
+    expect(modelRequiresThinking('claude-sonnet-5-5')).toBe(false)
+    expect(modelSupportsAdaptiveThinking('claude-sonnet-5-5')).toBe(false)
+
+    // A provider that declares the capabilities keeps the required adaptive mode.
+    process.env.ANTHROPIC_DEFAULT_SONNET_MODEL_SUPPORTED_CAPABILITIES =
+      'thinking,required_thinking,adaptive_thinking'
+    clearCapabilityCache()
+    expect(modelRequiresThinking('claude-sonnet-5-5')).toBe(true)
+    expect(modelSupportsAdaptiveThinking('claude-sonnet-5-5')).toBe(true)
+  })
+
+  test('defaults to medium effort while supporting every effort level', () => {
+    expect(getDefaultEffortForModel('claude-sonnet-5-5')).toBe('medium')
+    expect(getDefaultEffortForModel('claude-sonnet-5-5[1m]')).toBe('medium')
+    expect(modelSupportsEffort('claude-sonnet-5-5')).toBe(true)
+    expect(modelSupportsXHighEffort('claude-sonnet-5-5')).toBe(true)
+    expect(modelSupportsMaxEffort('claude-sonnet-5-5')).toBe(true)
+  })
+})
+
+describe('Sonnet 5.5 pricing', () => {
+  test('uses the published $2/$10 pricing, $2.50 cache writes and $0.20 cached reads', () => {
+    expect(getModelPricingString('claude-sonnet-5-5')).toBe('$2/$10 per Mtok')
+    for (const model of SONNET_55_VARIANTS) {
+      expect(
+        calculateCostFromTokens(model, {
+          inputTokens: 1_000_000,
+          outputTokens: 1_000_000,
+          cacheReadInputTokens: 1_000_000,
+          cacheCreationInputTokens: 1_000_000,
+        }),
+      ).toBeCloseTo(14.7, 10)
+    }
+  })
+
+  test('prices activity stats at the Sonnet 5.5 rate instead of the Sonnet 5 prefix rate', () => {
+    const expected = {
+      inputTokens: 2,
+      outputTokens: 10,
+      promptCacheWriteTokens: 2.5,
+      promptCacheReadTokens: 0.2,
+      webSearchRequests: 0.01,
+    }
+    for (const model of ['claude-sonnet-5-5', 'anthropic/claude-sonnet-5-5', 'claude-sonnet-5-5-20260928']) {
+      expect(resolveModelCosts(model)).toEqual(expected)
+    }
+  })
+})
diff --git a/src/utils/modelCost.ts b/src/utils/modelCost.ts
index 282e8827..2f3f25c8 100644
--- a/src/utils/modelCost.ts
+++ b/src/utils/modelCost.ts
@@ -16,9 +16,11 @@ import {
   CLAUDE_OPUS_4_8_CONFIG,
   CLAUDE_OPUS_4_CONFIG,
   CLAUDE_OPUS_5_5_CONFIG,
+  CLAUDE_OPUS_5_CONFIG,
   CLAUDE_SONNET_4_5_CONFIG,
   CLAUDE_SONNET_4_6_CONFIG,
   CLAUDE_SONNET_4_CONFIG,
+  CLAUDE_SONNET_5_5_CONFIG,
   CLAUDE_SONNET_5_CONFIG,
 } from './model/configs.js'
 import {
@@ -37,7 +39,7 @@ export type ModelCosts = {
   webSearchRequests: number
 }
 
-// Standard pricing tier for Sonnet models: $3 input / $15 output per Mtok
+// Pricing tier for Sonnet 4.x and earlier: $3 input / $15 output per Mtok
 export const COST_TIER_3_15 = {
   inputTokens: 3,
   outputTokens: 15,
@@ -46,6 +48,17 @@ export const COST_TIER_3_15 = {
   webSearchRequests: 0.01,
 } as const satisfies ModelCosts
 
+// Pricing tier for Sonnet 5 and Sonnet 5.5: $2 input / $10 output per Mtok.
+// Sonnet 5 launched at this price as introductory pricing; Anthropic made it the
+// standard price and cancelled the announced $3/$15 increase, so do not restore it.
+export const COST_TIER_2_10 = {
+  inputTokens: 2,
+  outputTokens: 10,
+  promptCacheWriteTokens: 2.5,
+  promptCacheReadTokens: 0.2,
+  webSearchRequests: 0.01,
+} as const satisfies ModelCosts
+
 // Pricing tier for Opus 4/4.1: $15 input / $75 output per Mtok
 export const COST_TIER_15_75 = {
   inputTokens: 15,
@@ -88,6 +101,16 @@ export const COST_OPUS_55 = {
   webSearchRequests: 0.01,
 } as const satisfies ModelCosts
 
+// Opus 5.5 fast mode (research preview): $8 input / $40 output per Mtok, with the cache
+// multipliers stacked on top (1.25x writes, 0.05x reads on Opus 5.5).
+export const COST_OPUS_55_FAST = {
+  inputTokens: 8,
+  outputTokens: 40,
+  promptCacheWriteTokens: 10,
+  promptCacheReadTokens: 0.4,
+  webSearchRequests: 0.01,
+} as const satisfies ModelCosts
+
 // Fast mode pricing for Opus 4.7: $30 input / $150 output per Mtok
 export const COST_TIER_30_150 = {
   inputTokens: 30,
@@ -132,6 +155,7 @@ export function getOpus46CostTier(fastMode: boolean): ModelCosts {
 // Web search cost: $10 per 1000 requests = $0.01 per request
 export const MODEL_COSTS: Record<ModelShortName, ModelCosts> = {
   [firstPartyNameToCanonical(CLAUDE_OPUS_5_5_CONFIG.firstParty)]: COST_OPUS_55,
+  [firstPartyNameToCanonical(CLAUDE_OPUS_5_CONFIG.firstParty)]: COST_TIER_5_25,
   [firstPartyNameToCanonical(CLAUDE_FABLE_5_1_CONFIG.firstParty)]:
     COST_FABLE_51,
   [firstPartyNameToCanonical(CLAUDE_FABLE_5_CONFIG.firstParty)]:
@@ -150,8 +174,10 @@ export const MODEL_COSTS: Record<ModelShortName, ModelCosts> = {
     COST_TIER_3_15,
   [firstPartyNameToCanonical(CLAUDE_SONNET_4_6_CONFIG.firstParty)]:
     COST_TIER_3_15,
+  [firstPartyNameToCanonical(CLAUDE_SONNET_5_5_CONFIG.firstParty)]:
+    COST_TIER_2_10,
   [firstPartyNameToCanonical(CLAUDE_SONNET_5_CONFIG.firstParty)]:
-    COST_TIER_3_15,
+    COST_TIER_2_10,
   [firstPartyNameToCanonical(CLAUDE_OPUS_4_CONFIG.firstParty)]: COST_TIER_15_75,
   [firstPartyNameToCanonical(CLAUDE_OPUS_4_1_CONFIG.firstParty)]:
     COST_TIER_15_75,
diff --git a/src/utils/modelCostParity.test.ts b/src/utils/modelCostParity.test.ts
new file mode 100644
index 00000000..7ddb119e
--- /dev/null
+++ b/src/utils/modelCostParity.test.ts
@@ -0,0 +1,42 @@
+import { describe, expect, it } from 'bun:test'
+import { ALL_MODEL_CONFIGS } from './model/configs.js'
+import { firstPartyNameToCanonical } from './model/model.js'
+import { MODEL_COSTS } from './modelCost.js'
+import { resolveModelCosts } from './usageAccounting.js'
+
+// Two independent tables price Claude models: `MODEL_COSTS` (canonical-name lookup, used for the
+// CLI's /cost) and the indexer's prefix table in usageAccounting (activity stats). A model added to
+// only one, or a shorter prefix such as `claude-sonnet-5` shadowing `claude-sonnet-5-5`, misprices
+// it without any error, so the two must agree for every model the app registers.
+const claudeModels = Object.entries(ALL_MODEL_CONFIGS).filter(([, config]) =>
+  config.firstParty.startsWith('claude-'),
+)
+
+describe('Claude model pricing tables', () => {
+  it.each(claudeModels)('%s is priced by both tables, identically', (_key, config) => {
+    const canonical = firstPartyNameToCanonical(config.firstParty)
+    expect(MODEL_COSTS[canonical]).toBeDefined()
+    expect(resolveModelCosts(config.firstParty)).toEqual(MODEL_COSTS[canonical]!)
+  })
+
+  // https://platform.claude.com/docs/en/about-claude/pricing (checked 2026-09-29), $ per MTok.
+  it.each([
+    ['claude-fable-5-1', 10, 50, 0.25],
+    ['claude-fable-5', 10, 50, 1],
+    ['claude-opus-5-5', 4, 20, 0.2],
+    ['claude-opus-5', 5, 25, 0.5],
+    ['claude-opus-4-8', 5, 25, 0.5],
+    ['claude-sonnet-5-5', 2, 10, 0.2],
+    ['claude-sonnet-5', 2, 10, 0.2],
+    ['claude-sonnet-4-6', 3, 15, 0.3],
+    ['claude-haiku-4-5', 1, 5, 0.1],
+  ])('%s matches the published input/output/cache-read prices', (model, input, output, cacheRead) => {
+    for (const costs of [MODEL_COSTS[firstPartyNameToCanonical(model)], resolveModelCosts(model)]) {
+      expect(costs).toMatchObject({
+        inputTokens: input,
+        outputTokens: output,
+        promptCacheReadTokens: cacheRead,
+      })
+    }
+  })
+})
diff --git a/src/utils/thinking.ts b/src/utils/thinking.ts
index fca8f4ae..74b112a8 100644
--- a/src/utils/thinking.ts
+++ b/src/utils/thinking.ts
@@ -86,6 +86,16 @@ export function getRainbowColor(
   return colors[charIndex % colors.length]!
 }
 
+// Fable, Opus 5.5 and Sonnet 5.5 reject `thinking: disabled` and manual budgets;
+// they always run adaptive thinking.
+function isAdaptiveOnlyModel(canonical: string): boolean {
+  return (
+    canonical.includes('claude-fable-5') ||
+    canonical === 'claude-opus-5-5' ||
+    canonical === 'claude-sonnet-5-5'
+  )
+}
+
 // TODO(inigo): add support for probing unknown models via API error detection
 // Provider-aware thinking support detection (aligns with modelSupportsISP in betas.ts)
 export function modelSupportsThinking(model: string): boolean {
@@ -101,9 +111,9 @@ export function modelSupportsThinking(model: string): boolean {
   // IMPORTANT: Do not change thinking support without notifying the model
   // launch DRI and research. This can greatly affect model quality and bashing.
   const canonical = getCanonicalName(model)
-  // Fable and Opus 5.5 use always-on adaptive thinking. Keep this after the provider
+  // Adaptive-only models use always-on adaptive thinking. Keep this after the provider
   // capability override so an explicitly incompatible 3P route can opt out.
-  if (canonical.includes('claude-fable-5') || canonical === 'claude-opus-5-5') {
+  if (isAdaptiveOnlyModel(canonical)) {
     return true
   }
   const provider = getAPIProvider()
@@ -126,8 +136,7 @@ export function modelRequiresThinking(model: string): boolean {
   if (required3P !== undefined) {
     return required3P
   }
-  const canonical = getCanonicalName(model)
-  return canonical.includes('claude-fable-5') || canonical === 'claude-opus-5-5'
+  return isAdaptiveOnlyModel(getCanonicalName(model))
 }
 
 /** Fable 5.1 binds replayed thinking to the preceding system, tools and history. */
@@ -154,9 +163,9 @@ export function modelSupportsAdaptiveThinking(model: string): boolean {
     return supported3P
   }
   const canonical = getCanonicalName(model)
-  // Fable and Opus 5.5 reject disabled/manual thinking and require adaptive thinking.
+  // Adaptive-only models reject disabled/manual thinking and require adaptive thinking.
   // Explicit 3P capability declarations above remain authoritative.
-  if (canonical.includes('claude-fable-5') || canonical === 'claude-opus-5-5') {
+  if (isAdaptiveOnlyModel(canonical)) {
     return true
   }
   const provider = getAPIProvider()
diff --git a/src/utils/usageAccounting.test.ts b/src/utils/usageAccounting.test.ts
index 0eea2cb8..81329e28 100644
--- a/src/utils/usageAccounting.test.ts
+++ b/src/utils/usageAccounting.test.ts
@@ -28,10 +28,33 @@ describe('resolveModelCosts', () => {
     expect(resolveModelCosts('claude-opus-4-8')?.inputTokens).toBe(5)
     expect(resolveModelCosts('claude-opus-4-1')?.inputTokens).toBe(15)
     expect(resolveModelCosts('claude-fable-5')?.outputTokens).toBe(50)
-    expect(resolveModelCosts('claude-sonnet-5')?.outputTokens).toBe(15)
     expect(resolveModelCosts('claude-haiku-4-5')?.outputTokens).toBe(5)
   })
 
+  it('prices Sonnet 5 at its published $2/$10, which replaced the announced $3/$15', () => {
+    expect(resolveModelCosts('claude-sonnet-5')).toEqual({
+      inputTokens: 2,
+      outputTokens: 10,
+      promptCacheWriteTokens: 2.5,
+      promptCacheReadTokens: 0.2,
+      webSearchRequests: 0.01,
+    })
+    // Sonnet 4.x keeps the older Sonnet rate.
+    expect(resolveModelCosts('claude-sonnet-4-6')).toMatchObject({ inputTokens: 3, outputTokens: 15 })
+  })
+
+  it('prices Opus 5.5 below Opus 5 rather than inheriting the shorter prefix', () => {
+    expect(resolveModelCosts('claude-opus-5-5')).toEqual({
+      inputTokens: 4,
+      outputTokens: 20,
+      promptCacheWriteTokens: 5,
+      promptCacheReadTokens: 0.2,
+      webSearchRequests: 0.01,
+    })
+    expect(resolveModelCosts('anthropic/claude-opus-5-5')).toEqual(resolveModelCosts('claude-opus-5-5')!)
+    expect(resolveModelCosts('claude-opus-5')).toMatchObject({ inputTokens: 5, outputTokens: 25 })
+  })
+
   it('sees through the decorations gateways and dated snapshots add', () => {
     const opus = resolveModelCosts('claude-opus-4-8')
     expect(resolveModelCosts('claude-opus-4-8-r')).toEqual(opus!)
@@ -44,6 +67,11 @@ describe('resolveModelCosts', () => {
     // `claude-opus-4-1` bills at the old Opus tier; a bare `claude-opus-4` must not swallow it.
     expect(resolveModelCosts('claude-opus-4-1')?.inputTokens).toBe(15)
     expect(resolveModelCosts('claude-opus-4-5')?.inputTokens).toBe(5)
+    // The same holds when a point release extends a whole-number model id.
+    expect(resolveModelCosts('claude-sonnet-5')?.inputTokens).toBe(2)
+    expect(resolveModelCosts('claude-sonnet-5-5')?.inputTokens).toBe(2)
+    expect(resolveModelCosts('claude-fable-5')?.promptCacheReadTokens).toBe(1)
+    expect(resolveModelCosts('claude-fable-5-1')?.promptCacheReadTokens).toBe(0.25)
   })
 
   it('returns null for third-party models instead of guessing Claude rates', () => {
@@ -69,7 +97,23 @@ describe('resolveModelCosts', () => {
     expect(resolveModelCosts('claude-opus-5', 'fast')?.inputTokens).toBe(10)
     expect(resolveModelCosts('claude-opus-5', 'standard')?.inputTokens).toBe(5)
     // Sonnet has no fast mode — a stray `speed` must not change what it costs.
-    expect(resolveModelCosts('claude-sonnet-5', 'fast')?.inputTokens).toBe(3)
+    expect(resolveModelCosts('claude-sonnet-5', 'fast')?.inputTokens).toBe(2)
+    expect(resolveModelCosts('claude-sonnet-5-5', 'fast')).toEqual(resolveModelCosts('claude-sonnet-5-5')!)
+  })
+
+  it('bills Opus 5.5 and Opus 4.8 fast mode at their published premiums', () => {
+    // https://platform.claude.com/docs/en/about-claude/pricing#fast-mode-pricing
+    expect(resolveModelCosts('claude-opus-5-5', 'fast')).toEqual({
+      inputTokens: 8,
+      outputTokens: 40,
+      promptCacheWriteTokens: 10,
+      promptCacheReadTokens: 0.4,
+      webSearchRequests: 0.01,
+    })
+    // Opus 5.5 must not inherit Opus 5's $10/$50 fast rate through the shorter prefix.
+    expect(resolveModelCosts('claude-opus-5', 'fast')).toMatchObject({ inputTokens: 10, outputTokens: 50 })
+    expect(resolveModelCosts('claude-opus-4-8', 'fast')).toMatchObject({ inputTokens: 10, outputTokens: 50 })
+    expect(resolveModelCosts('claude-opus-4-8', 'standard')).toMatchObject({ inputTokens: 5, outputTokens: 25 })
   })
 })
 
@@ -119,6 +163,37 @@ describe('estimateCostUSD', () => {
     expect(cost).toBeCloseTo(36.75, 10)
   })
 
+  it('bills Sonnet 5 and the newer Sonnet 5.5 identically at $2/$10', () => {
+    const million = tokens({
+      inputTokens: ONE_MILLION,
+      outputTokens: ONE_MILLION,
+      cacheReadInputTokens: ONE_MILLION,
+      cacheCreationInputTokens: ONE_MILLION,
+    })
+    // 2 input + 10 output + 0.20 cache read + 2.50 cache write
+    expect(estimateCostUSD('claude-sonnet-5', million)).toBeCloseTo(14.7, 10)
+    expect(estimateCostUSD('claude-sonnet-5-5', million)).toBeCloseTo(14.7, 10)
+  })
+
+  it('bills Opus 5.5 at $4/$20 with the 5%-of-input cache read rate', () => {
+    // 4 input + 20 output + 0.20 cache read + 5 cache write
+    expect(estimateCostUSD('claude-opus-5-5', tokens({
+      inputTokens: ONE_MILLION,
+      outputTokens: ONE_MILLION,
+      cacheReadInputTokens: ONE_MILLION,
+      cacheCreationInputTokens: ONE_MILLION,
+    }))).toBeCloseTo(29.2, 10)
+    expect(estimateCostUSD('claude-opus-5-5', tokens({ cacheReadInputTokens: ONE_MILLION })))
+      .toBeCloseTo(0.2, 10)
+  })
+
+  it('bills fast-mode usage at the fast rate and standard usage at the standard rate', () => {
+    const million = tokens({ inputTokens: ONE_MILLION, outputTokens: ONE_MILLION })
+    expect(estimateCostUSD('claude-opus-5-5', million, 'fast')).toBeCloseTo(48, 10)
+    expect(estimateCostUSD('claude-opus-5-5', million, 'standard')).toBeCloseTo(24, 10)
+    expect(estimateCostUSD('claude-opus-4-8', million, 'fast')).toBeCloseTo(60, 10)
+  })
+
   it('prices cache reads at a tenth of input, which is why token totals overstate spend', () => {
     const cacheRead = estimateCostUSD('claude-opus-5', tokens({ cacheReadInputTokens: ONE_MILLION }))
     const input = estimateCostUSD('claude-opus-5', tokens({ inputTokens: ONE_MILLION }))
diff --git a/src/utils/usageAccounting.ts b/src/utils/usageAccounting.ts
index 0ddf5b84..529e8d28 100644
--- a/src/utils/usageAccounting.ts
+++ b/src/utils/usageAccounting.ts
@@ -2,6 +2,9 @@ import {
   COST_FABLE_51,
   COST_HAIKU_35,
   COST_HAIKU_45,
+  COST_OPUS_55,
+  COST_OPUS_55_FAST,
+  COST_TIER_2_10,
   COST_TIER_3_15,
   COST_TIER_5_25,
   COST_TIER_10_50,
@@ -44,6 +47,7 @@ export type PricedTokens = {
 // @[MODEL LAUNCH]: add the new model's canonical prefix here alongside its entry in MODEL_COSTS.
 // Longest match wins, so a bare family name may sit next to its versioned variants.
 const MODEL_TIERS: ReadonlyArray<readonly [prefix: string, costs: ModelCosts]> = [
+  ['claude-opus-5-5', COST_OPUS_55],
   ['claude-opus-5', COST_TIER_5_25],
   ['claude-opus-4-8', COST_TIER_5_25],
   ['claude-opus-4-7', COST_TIER_5_25],
@@ -54,7 +58,8 @@ const MODEL_TIERS: ReadonlyArray<readonly [prefix: string, costs: ModelCosts]> =
   ['claude-fable-5', COST_TIER_10_50],
   ['claude-fable-5-1', COST_FABLE_51],
   ['claude-mythos-5', COST_TIER_10_50],
-  ['claude-sonnet-5', COST_TIER_3_15],
+  ['claude-sonnet-5-5', COST_TIER_2_10],
+  ['claude-sonnet-5', COST_TIER_2_10],
   ['claude-sonnet-4-6', COST_TIER_3_15],
   ['claude-sonnet-4-5', COST_TIER_3_15],
   ['claude-sonnet-4', COST_TIER_3_15],
@@ -68,7 +73,9 @@ const MODEL_TIERS: ReadonlyArray<readonly [prefix: string, costs: ModelCosts]> =
 
 // Fast mode bills at its own rate on the models that offer it; everything else ignores `speed`.
 const FAST_MODE_TIERS: ReadonlyArray<readonly [prefix: string, costs: ModelCosts]> = [
+  ['claude-opus-5-5', COST_OPUS_55_FAST],
   ['claude-opus-5', COST_TIER_10_50],
+  ['claude-opus-4-8', COST_TIER_10_50],
   ['claude-opus-4-7', COST_TIER_30_150],
 ]