diff --git a/docs/reports/hardening-inventory.json b/docs/reports/hardening-inventory.json
index c7a97bbc..b89917eb 100644
--- a/docs/reports/hardening-inventory.json
+++ b/docs/reports/hardening-inventory.json
@@ -739,7 +739,7 @@
         },
         {
           "file": "src/web-server/model-pricing.ts",
-          "loc": 1127
+          "loc": 1138
         },
         {
           "file": "src/cliproxy/config/generator.ts",
@@ -778,8 +778,8 @@
           "loc": 939
         },
         {
-          "file": "src/cliproxy/accounts/registry.ts",
-          "loc": 871
+          "file": "src/cliproxy/model-catalog.ts",
+          "loc": 884
         }
       ]
     }
diff --git a/docs/reports/hardening-inventory.md b/docs/reports/hardening-inventory.md
index ab01fc80..95856df3 100644
--- a/docs/reports/hardening-inventory.md
+++ b/docs/reports/hardening-inventory.md
@@ -93,7 +93,7 @@ Scope: `src/**/*.{ts,tsx,js,jsx,mjs,cjs}`
 | `src/web-server/routes/cliproxy-auth-routes.ts` | 1531 |
 | `src/cliproxy/auth/oauth-handler.ts` | 1510 |
 | `src/cursor/cursor-executor.ts` | 1234 |
-| `src/web-server/model-pricing.ts` | 1127 |
+| `src/web-server/model-pricing.ts` | 1138 |
 | `src/cliproxy/config/generator.ts` | 1109 |
 | `src/cliproxy/auth/oauth-process.ts` | 1048 |
 | `src/cliproxy/config/env-builder.ts` | 1045 |
@@ -103,5 +103,5 @@ Scope: `src/**/*.{ts,tsx,js,jsx,mjs,cjs}`
 | `src/cliproxy/quota/quota-manager.ts` | 954 |
 | `src/web-server/services/codex-dashboard-service.ts` | 940 |
 | `src/glmt/glmt-proxy.ts` | 939 |
-| `src/cliproxy/accounts/registry.ts` | 871 |
+| `src/cliproxy/model-catalog.ts` | 884 |
 
diff --git a/src/cliproxy/__tests__/thinking-validator.test.ts b/src/cliproxy/__tests__/thinking-validator.test.ts
index b6a47489..41be1a1a 100644
--- a/src/cliproxy/__tests__/thinking-validator.test.ts
+++ b/src/cliproxy/__tests__/thinking-validator.test.ts
@@ -60,6 +60,14 @@ describe('Thinking Validator', () => {
       expect(result.warning).toBeUndefined();
     });
 
+    it('should treat max as a distinct top tier on Claude Fable 5.1', () => {
+      // Fable 5.1 has always-on adaptive thinking steered only by effort level.
+      const result = validateThinking('claude', 'claude-fable-5-1', 'max');
+      expect(result.valid).toBe(true);
+      expect(result.value).toBe('max');
+      expect(result.warning).toBeUndefined();
+    });
+
     it('should treat max as a distinct top tier on Claude Fable 5', () => {
       // Fable 5 shares Opus 4.8's adaptive thinking surface; max must remain
       // distinct from xhigh.
diff --git a/src/cliproxy/config/extended-context-config.ts b/src/cliproxy/config/extended-context-config.ts
index 98115888..98fb26c9 100644
--- a/src/cliproxy/config/extended-context-config.ts
+++ b/src/cliproxy/config/extended-context-config.ts
@@ -10,10 +10,11 @@
  */
 
 import type { CLIProxyProvider } from '../types';
-import { supportsExtendedContext } from '../model-catalog';
+import { getDefaultFableTierModel, supportsExtendedContext } from '../model-catalog';
 import { warn } from '../../utils/ui';
 import {
   ANTHROPIC_MODEL_ENV_KEYS,
+  EXTENDED_CONTEXT_MODEL_ENV_KEYS,
   applyExtendedContextPreferenceToAnthropicModels,
   applyExtendedContextSuffix as applyExtendedContextSuffixShared,
   hasExtendedContextSuffix,
@@ -63,6 +64,39 @@ export function shouldApplyExtendedContext(
   return false;
 }
 
+/**
+ * Whether a saved Anthropic tier mapping still carries a [1m] suffix after the
+ * per-key pass, i.e. the launch is a long-context launch.
+ */
+function hasSavedLongContextTier(envVars: NodeJS.ProcessEnv): boolean {
+  return ANTHROPIC_MODEL_ENV_KEYS.some((key) => {
+    const value = envVars[key];
+    return typeof value === 'string' && hasExtendedContextSuffix(value);
+  });
+}
+
+/**
+ * Give a long-context launch a fable tier when the profile does not map one.
+ *
+ * Claude Code falls back to its own bare Fable id for `--model fable` / the
+ * fable tier, and behind a proxy base URL a bare natively-1M id is clamped to
+ * the standard 200k window. Only the [1m] suffix lifts that clamp, so a
+ * model-neutral claude profile that asked for 1M elsewhere would otherwise get
+ * a 200k Fable. An explicit mapping (dashboard "fable tier" field or settings
+ * file) always wins; providers without a catalog Fable model are untouched.
+ */
+function fillFableTierForLongContext(envVars: NodeJS.ProcessEnv, provider: CLIProxyProvider): void {
+  const existing = envVars.ANTHROPIC_DEFAULT_FABLE_MODEL;
+  if (typeof existing === 'string' && existing.trim().length > 0) {
+    return;
+  }
+  const fableModel = getDefaultFableTierModel(provider);
+  if (!fableModel || !supportsExtendedContext(provider, fableModel)) {
+    return;
+  }
+  envVars.ANTHROPIC_DEFAULT_FABLE_MODEL = applyExtendedContextSuffixShared(fableModel);
+}
+
 /**
  * Apply extended context configuration to env vars.
  * Modifies ANTHROPIC_MODEL and tier models with [1m] suffix.
@@ -88,6 +122,9 @@ export function applyExtendedContextConfig(
           ),
       })
     );
+    if (extendedContextOverride) {
+      fillFableTierForLongContext(envVars, provider);
+    }
     return;
   }
 
@@ -95,7 +132,7 @@ export function applyExtendedContextConfig(
   // previously saved [1m] preference just because the model is Claude — only
   // strip when the model no longer supports extended context. Native Gemini
   // models still get auto-toggled based on catalog support.
-  for (const key of ANTHROPIC_MODEL_ENV_KEYS) {
+  for (const key of EXTENDED_CONTEXT_MODEL_ENV_KEYS) {
     const value = envVars[key];
     if (typeof value !== 'string' || value.trim().length === 0) {
       continue;
@@ -113,4 +150,8 @@ export function applyExtendedContextConfig(
       envVars[key] = stripExtendedContextSuffix(value);
     }
   }
+
+  if (hasSavedLongContextTier(envVars)) {
+    fillFableTierForLongContext(envVars, provider);
+  }
 }
diff --git a/src/cliproxy/executor/__tests__/launch-settings.test.ts b/src/cliproxy/executor/__tests__/launch-settings.test.ts
index 6080ab27..0b313b84 100644
--- a/src/cliproxy/executor/__tests__/launch-settings.test.ts
+++ b/src/cliproxy/executor/__tests__/launch-settings.test.ts
@@ -57,6 +57,30 @@ describe('buildLaunchSettingsOverlay', () => {
     expect(env.ANTHROPIC_AUTH_TOKEN).toBe('ccs-internal-managed');
   });
 
+  it('overlays the extended-context extra model keys so a saved bare value cannot clobber --1m/--no-1m', () => {
+    writePersisted({
+      env: {
+        ANTHROPIC_BASE_URL: 'http://127.0.0.1:8317/api/provider/claude',
+        ANTHROPIC_MODEL: 'claude-opus-5[1m]',
+        ANTHROPIC_DEFAULT_MODEL: 'claude-opus-5[1m]',
+        CLAUDE_CODE_SUBAGENT_MODEL: 'claude-sonnet-5[1m]',
+      },
+    });
+
+    const { settings, changed } = buildLaunchSettingsOverlay(settingsPath, {
+      ANTHROPIC_BASE_URL: 'http://127.0.0.1:8317/api/provider/claude',
+      ANTHROPIC_MODEL: 'claude-opus-5',
+      ANTHROPIC_DEFAULT_MODEL: 'claude-opus-5',
+      CLAUDE_CODE_SUBAGENT_MODEL: 'claude-sonnet-5',
+    } as NodeJS.ProcessEnv);
+
+    expect(changed).toBe(true);
+    const env = settings.env as Record<string, string>;
+    expect(env.ANTHROPIC_MODEL).toBe('claude-opus-5');
+    expect(env.ANTHROPIC_DEFAULT_MODEL).toBe('claude-opus-5');
+    expect(env.CLAUDE_CODE_SUBAGENT_MODEL).toBe('claude-sonnet-5');
+  });
+
   it('preserves non-env settings (permissions, hooks, etc.)', () => {
     writePersisted({
       env: { ANTHROPIC_BASE_URL: 'http://127.0.0.1:8317/api/provider/codex' },
diff --git a/src/cliproxy/executor/launch-settings.ts b/src/cliproxy/executor/launch-settings.ts
index 5e33bf7e..aadbd96e 100644
--- a/src/cliproxy/executor/launch-settings.ts
+++ b/src/cliproxy/executor/launch-settings.ts
@@ -26,6 +26,7 @@ import * as os from 'os';
 import * as path from 'path';
 
 import { ANTHROPIC_MODEL_ENV_KEYS, ANTHROPIC_ROUTING_ENV_KEYS } from '../../utils/shell-executor';
+import { EXTRA_EXTENDED_CONTEXT_MODEL_ENV_KEYS } from '../../shared/extended-context-utils';
 
 // SIBLING HELPER: src/utils/openai-compat-launch-settings.ts solves the same
 // "persisted --settings env clobbers runtime routing env" problem by STRIPPING
@@ -38,9 +39,15 @@ import { ANTHROPIC_MODEL_ENV_KEYS, ANTHROPIC_ROUTING_ENV_KEYS } from '../../util
  * Environment keys that control provider routing/model selection and are read
  * by Claude from the settings `env` block. These must reflect the resolved
  * proxy-chain environment, not the persisted on-disk values. Reuses the
- * canonical routing/model key lists from shell-executor.
+ * canonical routing/model key lists from shell-executor, plus the extra model
+ * keys the [1m] preference manages (subagent + startup default): a saved bare
+ * value there would otherwise clobber the resolved --1m/--no-1m result.
  */
-const ROUTING_ENV_KEYS = [...ANTHROPIC_ROUTING_ENV_KEYS, ...ANTHROPIC_MODEL_ENV_KEYS];
+const ROUTING_ENV_KEYS = [
+  ...ANTHROPIC_ROUTING_ENV_KEYS,
+  ...ANTHROPIC_MODEL_ENV_KEYS,
+  ...EXTRA_EXTENDED_CONTEXT_MODEL_ENV_KEYS,
+];
 
 function isRecord(value: unknown): value is Record<string, unknown> {
   return typeof value === 'object' && value !== null && !Array.isArray(value);
diff --git a/src/cliproxy/model-catalog.ts b/src/cliproxy/model-catalog.ts
index ff2d632b..0b6cb2f8 100644
--- a/src/cliproxy/model-catalog.ts
+++ b/src/cliproxy/model-catalog.ts
@@ -531,10 +531,27 @@ export const MODEL_CATALOG: Partial<Record<CLIProxyProvider, ProviderCatalog>> =
         },
         extendedContext: true,
       },
+      {
+        id: 'claude-fable-5-1',
+        name: 'Claude Fable 5.1',
+        description: 'Most powerful model (1M context, 128K output)',
+        contextWindow: 1000000,
+        nativeImageInput: true,
+        // Thinking is always on and cannot be disabled: Anthropic rejects both
+        // `thinking.type: "disabled"` and manual budget_tokens with 400. Depth is
+        // steered only through effort levels (default `high`).
+        thinking: {
+          type: 'levels',
+          levels: ['low', 'medium', 'high', 'xhigh', 'max'],
+          maxLevel: 'max',
+          dynamicAllowed: true,
+        },
+        extendedContext: true,
+      },
       {
         id: 'claude-fable-5',
         name: 'Claude Fable 5',
-        description: 'Most powerful model',
+        description: 'Previous most powerful model',
         contextWindow: 1000000,
         nativeImageInput: true,
         // New tier above Opus. Same adaptive-thinking surface as Opus 4.8:
@@ -849,6 +866,17 @@ export function supportsExtendedContext(provider: CLIProxyProvider, modelId: str
   return model?.extendedContext === true;
 }
 
+/**
+ * Catalog model that backs the Claude Code `fable` tier for a provider.
+ * The catalog lists the newest Fable first, so the first match is the default.
+ * Returns undefined for providers that serve no Fable model.
+ */
+export function getDefaultFableTierModel(provider: CLIProxyProvider): string | undefined {
+  const catalog = MODEL_CATALOG[provider];
+  if (!catalog) return undefined;
+  return catalog.models.find((model) => model.id.toLowerCase().startsWith('claude-fable-'))?.id;
+}
+
 /**
  * Check if a model can read image inputs natively.
  */
diff --git a/src/shared/extended-context-utils.ts b/src/shared/extended-context-utils.ts
index 57468cef..ebed49c9 100644
--- a/src/shared/extended-context-utils.ts
+++ b/src/shared/extended-context-utils.ts
@@ -14,8 +14,43 @@ export const ANTHROPIC_MODEL_ENV_KEYS = [
 
 export type AnthropicModelEnvKey = (typeof ANTHROPIC_MODEL_ENV_KEYS)[number];
 
+/**
+ * Model env keys outside the Anthropic tier mappings that still carry a plain
+ * model id, so the extended-context preference has to cover them too. Kept
+ * separate from ANTHROPIC_MODEL_ENV_KEYS, which also drives routing, model-id
+ * normalization and profile validation.
+ *
+ * ANTHROPIC_DEFAULT_MODEL is Claude Code's lowest-priority startup model
+ * (after --model, ANTHROPIC_MODEL and the settings `model` field), so it needs
+ * the same [1m] treatment whenever a profile carries it.
+ */
+export const EXTRA_EXTENDED_CONTEXT_MODEL_ENV_KEYS = [
+  'CLAUDE_CODE_SUBAGENT_MODEL',
+  'ANTHROPIC_DEFAULT_MODEL',
+] as const;
+
+/** Every model env key the [1m] preference is applied to. */
+export const EXTENDED_CONTEXT_MODEL_ENV_KEYS = [
+  ...ANTHROPIC_MODEL_ENV_KEYS,
+  ...EXTRA_EXTENDED_CONTEXT_MODEL_ENV_KEYS,
+] as const;
+
+export type ExtendedContextModelEnvKey = (typeof EXTENDED_CONTEXT_MODEL_ENV_KEYS)[number];
+
 const ANTHROPIC_MODEL_ENV_KEY_SET = new Set<string>(ANTHROPIC_MODEL_ENV_KEYS);
 
+const EXTENDED_CONTEXT_MODEL_ENV_KEY_SET = new Set<string>(EXTENDED_CONTEXT_MODEL_ENV_KEYS);
+
+/*
+ * Why every key, including ANTHROPIC_DEFAULT_FABLE_MODEL, carries the suffix:
+ * Claude Code only grants a natively-1M model (Fable, Opus 5) its full window
+ * without the suffix when ANTHROPIC_BASE_URL is unset or points at
+ * api.anthropic.com. Behind any proxy (CLIProxy, headroom, ...) a bare id is
+ * clamped to 200k even when the backend advertises 1M, and the fable alias
+ * resolver passes the env value through untouched in that case. The [1m]
+ * suffix is therefore the only thing that turns the long window on for CCS.
+ */
+
 /** Check if model is a native Gemini model (auto-enabled behavior). */
 export function isNativeGeminiModel(modelId: string): boolean {
   return modelId.toLowerCase().startsWith('gemini-');
@@ -44,6 +79,11 @@ export function isAnthropicModelEnvKey(key: string): key is AnthropicModelEnvKey
   return ANTHROPIC_MODEL_ENV_KEY_SET.has(key);
 }
 
+/** True when key holds a model id the [1m] preference is applied to. */
+export function isExtendedContextModelEnvKey(key: string): key is ExtendedContextModelEnvKey {
+  return EXTENDED_CONTEXT_MODEL_ENV_KEY_SET.has(key);
+}
+
 /** Strip transient config suffixes so model IDs can be checked against catalogs. */
 export function stripModelConfigurationSuffixes(modelId: string): string {
   return stripExtendedContextSuffix(modelId.trim()).replace(/\([^)]+\)$/, '');
@@ -53,7 +93,7 @@ export function stripModelConfigurationSuffixes(modelId: string): string {
 export function hasAnthropicExtendedContextEnabled(
   env: Partial<Record<string, string | undefined>>
 ): boolean {
-  return ANTHROPIC_MODEL_ENV_KEYS.some((key) => {
+  return EXTENDED_CONTEXT_MODEL_ENV_KEYS.some((key) => {
     const value = env[key];
     return typeof value === 'string' && hasExtendedContextSuffix(value);
   });
@@ -66,12 +106,12 @@ export function applyExtendedContextPreferenceToAnthropicModels<
   env: T,
   enabled: boolean,
   options: {
-    supportsExtendedContext?: (modelId: string, key: AnthropicModelEnvKey) => boolean;
+    supportsExtendedContext?: (modelId: string, key: ExtendedContextModelEnvKey) => boolean;
   } = {}
 ): T {
   const nextEnv: Record<string, string | undefined> = { ...env };
 
-  for (const key of ANTHROPIC_MODEL_ENV_KEYS) {
+  for (const key of EXTENDED_CONTEXT_MODEL_ENV_KEYS) {
     const value = nextEnv[key];
     if (typeof value !== 'string' || value.trim().length === 0) {
       continue;
diff --git a/src/web-server/model-pricing.ts b/src/web-server/model-pricing.ts
index b4eec3e5..d1cdfacf 100644
--- a/src/web-server/model-pricing.ts
+++ b/src/web-server/model-pricing.ts
@@ -216,20 +216,21 @@ const PRICING_REGISTRY: Record<string, ModelPricing> = {
     cacheCreationPerMillion: 3.75,
     cacheReadPerMillion: 0.3,
   },
-  // Claude Sonnet 5 ($3/$15) — latest Sonnet; shares the standard Sonnet rates.
+  // Claude Sonnet 5 ($2/$10) — the launch introductory rate is now the standard
+  // price; Anthropic cancelled the scheduled 2026-09-01 increase to $3/$15.
   // Registered explicitly so it is a known model rather than relying on the
-  // unknown-model fallback that coincidentally matches these rates.
+  // unknown-model fallback.
   'claude-sonnet-5': {
-    inputPerMillion: 3.0,
-    outputPerMillion: 15.0,
-    cacheCreationPerMillion: 3.75,
-    cacheReadPerMillion: 0.3,
+    inputPerMillion: 2.0,
+    outputPerMillion: 10.0,
+    cacheCreationPerMillion: 2.5,
+    cacheReadPerMillion: 0.2,
   },
   'claude-sonnet-5-thinking': {
-    inputPerMillion: 3.0,
-    outputPerMillion: 15.0,
-    cacheCreationPerMillion: 3.75,
-    cacheReadPerMillion: 0.3,
+    inputPerMillion: 2.0,
+    outputPerMillion: 10.0,
+    cacheCreationPerMillion: 2.5,
+    cacheReadPerMillion: 0.2,
   },
   // Claude 4 Opus ($15/$75)
   'claude-4-opus-20250514': {
@@ -360,6 +361,16 @@ const PRICING_REGISTRY: Record<string, ModelPricing> = {
     cacheCreationPerMillion: 12.5,
     cacheReadPerMillion: 1.0,
   },
+  // Claude Fable 5.1 ($10/$50) — same tier and base rates as Fable 5, but cache
+  // hits are billed at 0.025x base input ($0.25/MTok) instead of the usual 0.1x.
+  // Anthropic applies that reduced multiplier only to Fable 5.1 and Mythos 5.1,
+  // so this entry cannot use CACHE_READ_MULTIPLIER-derived rates.
+  'claude-fable-5-1': {
+    inputPerMillion: 10.0,
+    outputPerMillion: 50.0,
+    cacheCreationPerMillion: 12.5,
+    cacheReadPerMillion: 0.25,
+  },
 
   // ---------------------------------------------------------------------------
   // OpenAI Models - Source: better-ccusage
diff --git a/tests/unit/cliproxy/extended-context-config.test.ts b/tests/unit/cliproxy/extended-context-config.test.ts
new file mode 100644
index 00000000..b8422b9f
--- /dev/null
+++ b/tests/unit/cliproxy/extended-context-config.test.ts
@@ -0,0 +1,117 @@
+import { describe, expect, it } from 'bun:test';
+
+import { applyExtendedContextConfig } from '../../../src/cliproxy/config/extended-context-config';
+
+describe('applyExtendedContextConfig', () => {
+  it('keeps a saved [1m] on the fable tier key in auto mode', () => {
+    const env: NodeJS.ProcessEnv = {
+      ANTHROPIC_MODEL: 'claude-opus-5[1m]',
+      ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1[1m]',
+    };
+
+    applyExtendedContextConfig(env, 'claude');
+
+    expect(env.ANTHROPIC_DEFAULT_FABLE_MODEL).toBe('claude-fable-5-1[1m]');
+    expect(env.ANTHROPIC_MODEL).toBe('claude-opus-5[1m]');
+  });
+
+  it('suffixes the fable tier key like every other tier when forced on', () => {
+    const env: NodeJS.ProcessEnv = {
+      ANTHROPIC_MODEL: 'claude-fable-5-1',
+      ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1',
+      CLAUDE_CODE_SUBAGENT_MODEL: 'claude-fable-5-1',
+    };
+
+    applyExtendedContextConfig(env, 'claude', true);
+
+    expect(env.ANTHROPIC_DEFAULT_FABLE_MODEL).toBe('claude-fable-5-1[1m]');
+    expect(env.ANTHROPIC_MODEL).toBe('claude-fable-5-1[1m]');
+    expect(env.CLAUDE_CODE_SUBAGENT_MODEL).toBe('claude-fable-5-1[1m]');
+  });
+
+  it('strips the fable tier key with the others when forced off', () => {
+    const env: NodeJS.ProcessEnv = {
+      ANTHROPIC_MODEL: 'claude-opus-5[1m]',
+      ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1[1m]',
+    };
+
+    applyExtendedContextConfig(env, 'claude', false);
+
+    expect(env.ANTHROPIC_DEFAULT_FABLE_MODEL).toBe('claude-fable-5-1');
+    expect(env.ANTHROPIC_MODEL).toBe('claude-opus-5');
+  });
+
+  describe('fable tier default on the claude provider', () => {
+    it('fills a missing fable tier with the catalog Fable model plus [1m] when a saved tier carries [1m]', () => {
+      const env: NodeJS.ProcessEnv = {
+        ANTHROPIC_MODEL: 'claude-opus-5[1m]',
+      };
+
+      applyExtendedContextConfig(env, 'claude');
+
+      expect(env.ANTHROPIC_DEFAULT_FABLE_MODEL).toBe('claude-fable-5-1[1m]');
+    });
+
+    it('fills a missing fable tier when --1m is passed', () => {
+      const env: NodeJS.ProcessEnv = {
+        ANTHROPIC_MODEL: 'claude-opus-5',
+      };
+
+      applyExtendedContextConfig(env, 'claude', true);
+
+      expect(env.ANTHROPIC_MODEL).toBe('claude-opus-5[1m]');
+      expect(env.ANTHROPIC_DEFAULT_FABLE_MODEL).toBe('claude-fable-5-1[1m]');
+    });
+
+    it('fills a missing fable tier on a model-neutral claude launch when --1m is passed', () => {
+      const env: NodeJS.ProcessEnv = {};
+
+      applyExtendedContextConfig(env, 'claude', true);
+
+      expect(env.ANTHROPIC_DEFAULT_FABLE_MODEL).toBe('claude-fable-5-1[1m]');
+      expect(Object.keys(env)).toEqual(['ANTHROPIC_DEFAULT_FABLE_MODEL']);
+    });
+
+    it('leaves the fable tier alone when no long-context intent exists', () => {
+      const env: NodeJS.ProcessEnv = {
+        ANTHROPIC_MODEL: 'claude-opus-5',
+      };
+
+      applyExtendedContextConfig(env, 'claude');
+
+      expect(env.ANTHROPIC_DEFAULT_FABLE_MODEL).toBeUndefined();
+    });
+
+    it('leaves the fable tier alone when --no-1m is passed', () => {
+      const env: NodeJS.ProcessEnv = {
+        ANTHROPIC_MODEL: 'claude-opus-5[1m]',
+      };
+
+      applyExtendedContextConfig(env, 'claude', false);
+
+      expect(env.ANTHROPIC_MODEL).toBe('claude-opus-5');
+      expect(env.ANTHROPIC_DEFAULT_FABLE_MODEL).toBeUndefined();
+    });
+
+    it('never overrides an explicit fable tier mapping', () => {
+      const env: NodeJS.ProcessEnv = {
+        ANTHROPIC_MODEL: 'claude-opus-5[1m]',
+        ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5[1m]',
+      };
+
+      applyExtendedContextConfig(env, 'claude');
+
+      expect(env.ANTHROPIC_DEFAULT_FABLE_MODEL).toBe('claude-fable-5[1m]');
+    });
+
+    it('does not invent a fable tier for providers without Fable models', () => {
+      const env: NodeJS.ProcessEnv = {
+        ANTHROPIC_MODEL: 'gpt-5.4[1m]',
+      };
+
+      applyExtendedContextConfig(env, 'codex');
+
+      expect(env.ANTHROPIC_DEFAULT_FABLE_MODEL).toBeUndefined();
+    });
+  });
+});
diff --git a/tests/unit/model-pricing.test.ts b/tests/unit/model-pricing.test.ts
index 2df898fc..8202db38 100644
--- a/tests/unit/model-pricing.test.ts
+++ b/tests/unit/model-pricing.test.ts
@@ -277,12 +277,24 @@ describe('model-pricing', () => {
       expect(fable5.cacheReadPerMillion).toBe(1.0);
     });
 
+    it('should return correct pricing for Claude Fable 5.1', () => {
+      // Same base rates as Fable 5, but cache hits bill at 0.025x base input
+      // ($0.25/MTok) rather than the standard 0.1x multiplier.
+      const fable51 = getModelPricing('claude-fable-5-1');
+      expect(fable51.inputPerMillion).toBe(10.0);
+      expect(fable51.outputPerMillion).toBe(50.0);
+      expect(fable51.cacheCreationPerMillion).toBe(12.5);
+      expect(fable51.cacheReadPerMillion).toBe(0.25);
+    });
+
     it('should return correct pricing for Claude Sonnet 5', () => {
+      // The $2/$10 launch introductory rate became the standard price; the
+      // scheduled 2026-09-01 increase to $3/$15 was cancelled.
       const sonnet5 = getModelPricing('claude-sonnet-5');
-      expect(sonnet5.inputPerMillion).toBe(3.0);
-      expect(sonnet5.outputPerMillion).toBe(15.0);
-      expect(sonnet5.cacheCreationPerMillion).toBe(3.75);
-      expect(sonnet5.cacheReadPerMillion).toBe(0.3);
+      expect(sonnet5.inputPerMillion).toBe(2.0);
+      expect(sonnet5.outputPerMillion).toBe(10.0);
+      expect(sonnet5.cacheCreationPerMillion).toBe(2.5);
+      expect(sonnet5.cacheReadPerMillion).toBe(0.2);
     });
 
     it('should return Opus-tier pricing for Claude Opus 5', () => {
@@ -430,7 +442,7 @@ describe('model-pricing', () => {
         cacheReadTokens: 1_000_000,
       };
       const cost = calculateCost(usage, 'claude-sonnet-5');
-      expect(cost).toBe(22.05); // 3 + 15 + 3.75 + 0.3
+      expect(cost).toBe(14.7); // 2 + 10 + 2.5 + 0.2
     });
 
     it('should calculate fast-tier Claude Opus 4.8 cost (2x premium)', () => {
diff --git a/tests/unit/shared/extended-context-utils.test.ts b/tests/unit/shared/extended-context-utils.test.ts
index 3694f74c..c1ce474a 100644
--- a/tests/unit/shared/extended-context-utils.test.ts
+++ b/tests/unit/shared/extended-context-utils.test.ts
@@ -2,7 +2,11 @@ import { describe, expect, it } from 'bun:test';
 
 import {
   ANTHROPIC_MODEL_ENV_KEYS,
+  EXTENDED_CONTEXT_MODEL_ENV_KEYS,
+  applyExtendedContextPreferenceToAnthropicModels,
+  hasAnthropicExtendedContextEnabled,
   isAnthropicModelEnvKey,
+  isExtendedContextModelEnvKey,
 } from '../../../src/shared/extended-context-utils';
 
 describe('Anthropic model env keys', () => {
@@ -22,3 +26,96 @@ describe('Anthropic model env keys', () => {
     expect(isAnthropicModelEnvKey('ANTHROPIC_BASE_URL')).toBe(false);
   });
 });
+
+describe('extended-context model env keys', () => {
+  it('covers the Anthropic tiers plus the subagent and startup-default model keys', () => {
+    expect([...EXTENDED_CONTEXT_MODEL_ENV_KEYS]).toEqual([
+      ...ANTHROPIC_MODEL_ENV_KEYS,
+      'CLAUDE_CODE_SUBAGENT_MODEL',
+      'ANTHROPIC_DEFAULT_MODEL',
+    ]);
+    expect(isExtendedContextModelEnvKey('CLAUDE_CODE_SUBAGENT_MODEL')).toBe(true);
+    expect(isExtendedContextModelEnvKey('ANTHROPIC_DEFAULT_MODEL')).toBe(true);
+    expect(isAnthropicModelEnvKey('CLAUDE_CODE_SUBAGENT_MODEL')).toBe(false);
+    expect(isAnthropicModelEnvKey('ANTHROPIC_DEFAULT_MODEL')).toBe(false);
+  });
+});
+
+describe('applyExtendedContextPreferenceToAnthropicModels', () => {
+  it('writes [1m] into every managed key, the fable tier included', () => {
+    // Behind a proxy base URL Claude Code clamps a bare Fable id to 200k, so the
+    // fable tier needs the suffix exactly like the opus/sonnet tiers do.
+    const env = applyExtendedContextPreferenceToAnthropicModels(
+      {
+        ANTHROPIC_MODEL: 'claude-fable-5-1',
+        ANTHROPIC_DEFAULT_OPUS_MODEL: 'claude-opus-5',
+        ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1',
+        CLAUDE_CODE_SUBAGENT_MODEL: 'claude-fable-5-1',
+      },
+      true
+    );
+
+    expect(env).toEqual({
+      ANTHROPIC_MODEL: 'claude-fable-5-1[1m]',
+      ANTHROPIC_DEFAULT_OPUS_MODEL: 'claude-opus-5[1m]',
+      ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1[1m]',
+      CLAUDE_CODE_SUBAGENT_MODEL: 'claude-fable-5-1[1m]',
+    });
+  });
+
+  it('strips every managed key when the preference is off', () => {
+    const env = applyExtendedContextPreferenceToAnthropicModels(
+      {
+        ANTHROPIC_MODEL: 'claude-opus-5[1m]',
+        ANTHROPIC_DEFAULT_MODEL: 'claude-opus-5[1m]',
+        ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1[1m]',
+        CLAUDE_CODE_SUBAGENT_MODEL: 'claude-fable-5-1[1m]',
+      },
+      false
+    );
+
+    expect(env).toEqual({
+      ANTHROPIC_MODEL: 'claude-opus-5',
+      ANTHROPIC_DEFAULT_MODEL: 'claude-opus-5',
+      ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1',
+      CLAUDE_CODE_SUBAGENT_MODEL: 'claude-fable-5-1',
+    });
+  });
+
+  it('suffixes the startup-default model key when the preference is on', () => {
+    const env = applyExtendedContextPreferenceToAnthropicModels(
+      { ANTHROPIC_DEFAULT_MODEL: 'claude-opus-5' },
+      true
+    );
+
+    expect(env).toEqual({ ANTHROPIC_DEFAULT_MODEL: 'claude-opus-5[1m]' });
+  });
+
+  it('honors a caller compatibility predicate', () => {
+    const env = applyExtendedContextPreferenceToAnthropicModels(
+      {
+        ANTHROPIC_MODEL: 'claude-opus-5',
+        ANTHROPIC_DEFAULT_HAIKU_MODEL: 'claude-haiku-4-5-20251001',
+      },
+      true,
+      { supportsExtendedContext: (modelId) => !modelId.startsWith('claude-haiku-') }
+    );
+
+    expect(env).toEqual({
+      ANTHROPIC_MODEL: 'claude-opus-5[1m]',
+      ANTHROPIC_DEFAULT_HAIKU_MODEL: 'claude-haiku-4-5-20251001',
+    });
+  });
+
+  it('reads saved intent from any managed key', () => {
+    expect(
+      hasAnthropicExtendedContextEnabled({ CLAUDE_CODE_SUBAGENT_MODEL: 'claude-fable-5-1[1m]' })
+    ).toBe(true);
+    expect(
+      hasAnthropicExtendedContextEnabled({ ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1[1m]' })
+    ).toBe(true);
+    expect(
+      hasAnthropicExtendedContextEnabled({ ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1' })
+    ).toBe(false);
+  });
+});
diff --git a/ui/src/components/cliproxy/provider-editor/use-provider-editor.ts b/ui/src/components/cliproxy/provider-editor/use-provider-editor.ts
index 35ac28b1..6bec47a4 100644
--- a/ui/src/components/cliproxy/provider-editor/use-provider-editor.ts
+++ b/ui/src/components/cliproxy/provider-editor/use-provider-editor.ts
@@ -12,7 +12,7 @@ import type { ProviderCatalog } from '../provider-model-selector';
 import {
   applyExtendedContextPreferenceToAnthropicModels,
   hasAnthropicExtendedContextEnabled,
-  isAnthropicModelEnvKey,
+  isExtendedContextModelEnvKey,
 } from '@/lib/extended-context-utils';
 import { supportsExtendedContext } from '@/lib/model-catalogs';
 import { isValidProvider } from '@/lib/provider-config';
@@ -104,7 +104,7 @@ export function useProviderEditor(
   const updateEnvValue = useCallback(
     (key: string, value: string) => {
       const newEnv = { ...(currentSettings?.env || {}), [key]: value };
-      const envWithIntent = isAnthropicModelEnvKey(key)
+      const envWithIntent = isExtendedContextModelEnvKey(key)
         ? applySavedLongContextIntent(newEnv, extendedContextEnabled)
         : newEnv;
       delete envWithIntent['CCS_EXTENDED_CONTEXT'];
@@ -132,7 +132,7 @@ export function useProviderEditor(
   const updateEnvValues = useCallback(
     (updates: Record<string, string>) => {
       const newEnv = { ...(currentSettings?.env || {}), ...updates };
-      const touchesAnthropicModel = Object.keys(updates).some(isAnthropicModelEnvKey);
+      const touchesAnthropicModel = Object.keys(updates).some(isExtendedContextModelEnvKey);
       const envWithIntent = touchesAnthropicModel
         ? applySavedLongContextIntent(newEnv, extendedContextEnabled)
         : newEnv;
diff --git a/ui/src/lib/extended-context-utils.ts b/ui/src/lib/extended-context-utils.ts
index 2ce76d69..1dbb35b8 100644
--- a/ui/src/lib/extended-context-utils.ts
+++ b/ui/src/lib/extended-context-utils.ts
@@ -4,10 +4,13 @@
 
 export {
   ANTHROPIC_MODEL_ENV_KEYS,
+  EXTENDED_CONTEXT_MODEL_ENV_KEYS,
   EXTENDED_CONTEXT_SUFFIX,
+  EXTRA_EXTENDED_CONTEXT_MODEL_ENV_KEYS,
   applyExtendedContextPreferenceToAnthropicModels,
   isNativeGeminiModel,
   isAnthropicModelEnvKey,
+  isExtendedContextModelEnvKey,
   hasAnthropicExtendedContextEnabled,
   hasExtendedContextSuffix,
   applyExtendedContextSuffix,
diff --git a/ui/src/lib/model-catalogs.ts b/ui/src/lib/model-catalogs.ts
index 32c3d523..265e49e9 100644
--- a/ui/src/lib/model-catalogs.ts
+++ b/ui/src/lib/model-catalogs.ts
@@ -977,10 +977,22 @@ export const MODEL_CATALOGS: Record<string, ProviderCatalog> = {
           haiku: 'claude-haiku-4-5-20251001',
         },
       },
+      {
+        id: 'claude-fable-5-1',
+        name: 'Claude Fable 5.1',
+        description: 'Most powerful model',
+        extendedContext: true,
+        presetMapping: {
+          default: 'claude-fable-5-1',
+          opus: 'claude-fable-5-1',
+          sonnet: 'claude-sonnet-5',
+          haiku: 'claude-haiku-4-5-20251001',
+        },
+      },
       {
         id: 'claude-fable-5',
         name: 'Claude Fable 5',
-        description: 'Most powerful model',
+        description: 'Previous most powerful model',
         extendedContext: true,
         presetMapping: {
           default: 'claude-fable-5',
diff --git a/ui/tests/unit/ui/lib/preset-utils.test.ts b/ui/tests/unit/ui/lib/preset-utils.test.ts
index 06615ca0..d8ce4632 100644
--- a/ui/tests/unit/ui/lib/preset-utils.test.ts
+++ b/ui/tests/unit/ui/lib/preset-utils.test.ts
@@ -22,6 +22,7 @@ describe('claude preset utils', () => {
 
     expect(claudeCatalog.defaultModel).toBe('claude-sonnet-5');
     expect(ids).toContain('claude-sonnet-5');
+    expect(ids).toContain('claude-fable-5-1');
     expect(ids).toContain('claude-fable-5');
     expect(ids).toContain('claude-opus-5');
     expect(ids).toContain('claude-opus-4-8');