diff --git a/src/cliproxy/config/extended-context-config.ts b/src/cliproxy/config/extended-context-config.ts
index 443591d9..98fb26c9 100644
--- a/src/cliproxy/config/extended-context-config.ts
+++ b/src/cliproxy/config/extended-context-config.ts
@@ -10,13 +10,13 @@
  */
 
 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,
-  envKeyAcceptsExtendedContextSuffix,
   hasExtendedContextSuffix,
   isNativeGeminiModel,
   stripExtendedContextSuffix,
@@ -64,6 +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.
@@ -89,6 +122,9 @@ export function applyExtendedContextConfig(
           ),
       })
     );
+    if (extendedContextOverride) {
+      fillFableTierForLongContext(envVars, provider);
+    }
     return;
   }
 
@@ -103,13 +139,6 @@ export function applyExtendedContextConfig(
     }
     const modelId = stripModelConfigurationSuffixes(value);
 
-    // Keys whose resolver strips [1m] must never keep a saved suffix: the
-    // stripped value loses the model's native long context window.
-    if (!envKeyAcceptsExtendedContextSuffix(key)) {
-      envVars[key] = stripExtendedContextSuffix(value);
-      continue;
-    }
-
     if (isNativeGeminiModel(modelId)) {
       envVars[key] = supportsExtendedContext(provider, modelId)
         ? applyExtendedContextSuffixShared(value)
@@ -121,4 +150,8 @@ export function applyExtendedContextConfig(
       envVars[key] = stripExtendedContextSuffix(value);
     }
   }
+
+  if (hasSavedLongContextTier(envVars)) {
+    fillFableTierForLongContext(envVars, provider);
+  }
 }
diff --git a/src/cliproxy/model-catalog.ts b/src/cliproxy/model-catalog.ts
index 509639bc..0b6cb2f8 100644
--- a/src/cliproxy/model-catalog.ts
+++ b/src/cliproxy/model-catalog.ts
@@ -866,6 +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 78419abd..8c717720 100644
--- a/src/shared/extended-context-utils.ts
+++ b/src/shared/extended-context-utils.ts
@@ -34,21 +34,15 @@ 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);
 
-/**
- * Keys whose value Claude Code resolves through a resolver that removes [1m]
- * before use. ANTHROPIC_DEFAULT_FABLE_MODEL is the only one today: its resolver
- * strips the suffix (unlike the opus/sonnet resolvers, which pass the value
- * through), and the stripped env-supplied default is then held to the standard
- * 200k window instead of the model's native 1M. Writing [1m] here therefore
- * costs the long context window rather than granting it, and Fable models are
- * natively 1M, so the suffix is never needed on this key.
+/*
+ * 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.
  */
-const SUFFIX_STRIPPING_MODEL_ENV_KEYS = new Set<string>(['ANTHROPIC_DEFAULT_FABLE_MODEL']);
-
-/** True when writing an explicit [1m] suffix into this env key is meaningful. */
-export function envKeyAcceptsExtendedContextSuffix(key: string): boolean {
-  return !SUFFIX_STRIPPING_MODEL_ENV_KEYS.has(key);
-}
 
 /** Check if model is a native Gemini model (auto-enabled behavior). */
 export function isNativeGeminiModel(modelId: string): boolean {
@@ -117,9 +111,7 @@ export function applyExtendedContextPreferenceToAnthropicModels<
     }
 
     const modelId = stripModelConfigurationSuffixes(value);
-    const supported =
-      envKeyAcceptsExtendedContextSuffix(key) &&
-      (options.supportsExtendedContext?.(modelId, key) ?? true);
+    const supported = options.supportsExtendedContext?.(modelId, key) ?? true;
     nextEnv[key] =
       enabled && supported ? applyExtendedContextSuffix(value) : stripExtendedContextSuffix(value);
   }
diff --git a/tests/unit/cliproxy/extended-context-config.test.ts b/tests/unit/cliproxy/extended-context-config.test.ts
index 29b7a575..b8422b9f 100644
--- a/tests/unit/cliproxy/extended-context-config.test.ts
+++ b/tests/unit/cliproxy/extended-context-config.test.ts
@@ -3,7 +3,7 @@ import { describe, expect, it } from 'bun:test';
 import { applyExtendedContextConfig } from '../../../src/cliproxy/config/extended-context-config';
 
 describe('applyExtendedContextConfig', () => {
-  it('strips a saved [1m] from the fable tier key in auto mode', () => {
+  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]',
@@ -11,11 +11,11 @@ describe('applyExtendedContextConfig', () => {
 
     applyExtendedContextConfig(env, 'claude');
 
-    expect(env.ANTHROPIC_DEFAULT_FABLE_MODEL).toBe('claude-fable-5-1');
+    expect(env.ANTHROPIC_DEFAULT_FABLE_MODEL).toBe('claude-fable-5-1[1m]');
     expect(env.ANTHROPIC_MODEL).toBe('claude-opus-5[1m]');
   });
 
-  it('keeps the fable tier key plain when extended context is forced on', () => {
+  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',
@@ -24,8 +24,94 @@ describe('applyExtendedContextConfig', () => {
 
     applyExtendedContextConfig(env, 'claude', true);
 
-    expect(env.ANTHROPIC_DEFAULT_FABLE_MODEL).toBe('claude-fable-5-1');
+    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/shared/extended-context-utils.test.ts b/tests/unit/shared/extended-context-utils.test.ts
index bb319ce1..a65af8b1 100644
--- a/tests/unit/shared/extended-context-utils.test.ts
+++ b/tests/unit/shared/extended-context-utils.test.ts
@@ -4,7 +4,6 @@ import {
   ANTHROPIC_MODEL_ENV_KEYS,
   EXTENDED_CONTEXT_MODEL_ENV_KEYS,
   applyExtendedContextPreferenceToAnthropicModels,
-  envKeyAcceptsExtendedContextSuffix,
   hasAnthropicExtendedContextEnabled,
   isAnthropicModelEnvKey,
   isExtendedContextModelEnvKey,
@@ -37,22 +36,17 @@ describe('extended-context model env keys', () => {
     expect(isExtendedContextModelEnvKey('CLAUDE_CODE_SUBAGENT_MODEL')).toBe(true);
     expect(isAnthropicModelEnvKey('CLAUDE_CODE_SUBAGENT_MODEL')).toBe(false);
   });
-
-  it('marks the fable tier key as suffix-stripping', () => {
-    expect(envKeyAcceptsExtendedContextSuffix('ANTHROPIC_DEFAULT_FABLE_MODEL')).toBe(false);
-    expect(envKeyAcceptsExtendedContextSuffix('ANTHROPIC_MODEL')).toBe(true);
-    expect(envKeyAcceptsExtendedContextSuffix('ANTHROPIC_DEFAULT_OPUS_MODEL')).toBe(true);
-    expect(envKeyAcceptsExtendedContextSuffix('CLAUDE_CODE_SUBAGENT_MODEL')).toBe(true);
-  });
 });
 
 describe('applyExtendedContextPreferenceToAnthropicModels', () => {
-  it('never writes [1m] into the fable tier key and strips a saved one', () => {
+  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[1m]',
+        ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1',
         CLAUDE_CODE_SUBAGENT_MODEL: 'claude-fable-5-1',
       },
       true
@@ -61,7 +55,7 @@ describe('applyExtendedContextPreferenceToAnthropicModels', () => {
     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',
+      ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1[1m]',
       CLAUDE_CODE_SUBAGENT_MODEL: 'claude-fable-5-1[1m]',
     });
   });
@@ -83,7 +77,7 @@ describe('applyExtendedContextPreferenceToAnthropicModels', () => {
     });
   });
 
-  it('honors a caller compatibility predicate on top of the key guard', () => {
+  it('honors a caller compatibility predicate', () => {
     const env = applyExtendedContextPreferenceToAnthropicModels(
       {
         ANTHROPIC_MODEL: 'claude-opus-5',
@@ -99,10 +93,13 @@ describe('applyExtendedContextPreferenceToAnthropicModels', () => {
     });
   });
 
-  it('reads saved intent from the subagent key too', () => {
+  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/lib/extended-context-utils.ts b/ui/src/lib/extended-context-utils.ts
index aa7fde05..1dbb35b8 100644
--- a/ui/src/lib/extended-context-utils.ts
+++ b/ui/src/lib/extended-context-utils.ts
@@ -8,7 +8,6 @@ export {
   EXTENDED_CONTEXT_SUFFIX,
   EXTRA_EXTENDED_CONTEXT_MODEL_ENV_KEYS,
   applyExtendedContextPreferenceToAnthropicModels,
-  envKeyAcceptsExtendedContextSuffix,
   isNativeGeminiModel,
   isAnthropicModelEnvKey,
   isExtendedContextModelEnvKey,