diff --git a/src/server/__tests__/providers.test.ts b/src/server/__tests__/providers.test.ts
index 8bd7fbed..8d215bbd 100644
--- a/src/server/__tests__/providers.test.ts
+++ b/src/server/__tests__/providers.test.ts
@@ -355,6 +355,12 @@ describe('ProviderService', () => {
         expect(env.ANTHROPIC_DEFAULT_SONNET_MODEL).toBe('gpt-5.4')
         expect(env.ANTHROPIC_DEFAULT_OPUS_MODEL).toBe('gpt-5.3-codex')
         expect(typeof env.CLAUDE_CODE_MODEL_CONTEXT_WINDOWS).toBe('string')
+        expect(JSON.parse(env.CLAUDE_CODE_MODEL_CONTEXT_WINDOWS)).toEqual({
+          'gpt-5.3-codex': 258_400,
+          'gpt-5.4': 950_000,
+          'gpt-5.5': 258_400,
+          'gpt-5.4-mini': 258_400,
+        })
         expect(env.ANTHROPIC_BASE_URL).toBeUndefined()
         expect(env.ANTHROPIC_API_KEY).toBeUndefined()
         expect(env.ANTHROPIC_AUTH_TOKEN).toBeUndefined()
diff --git a/src/server/services/openaiOfficialProvider.ts b/src/server/services/openaiOfficialProvider.ts
index 5d39cbc4..bfc05a06 100644
--- a/src/server/services/openaiOfficialProvider.ts
+++ b/src/server/services/openaiOfficialProvider.ts
@@ -1,9 +1,10 @@
 import { OPENAI_CODEX_API_ENDPOINT } from '../../services/openaiAuth/client.js'
 import {
+  OPENAI_CODEX_MODEL_CATALOG,
   OPENAI_DEFAULT_HAIKU_MODEL,
   OPENAI_DEFAULT_MAIN_MODEL,
   OPENAI_DEFAULT_SONNET_MODEL,
-  getOpenAIContextWindowForModel,
+  getOpenAICodexContextWindowForModel,
 } from '../../services/openaiAuth/models.js'
 import { MODEL_CONTEXT_WINDOWS_ENV_KEY } from '../../utils/model/modelContextWindows.js'
 import { getHahaOpenAIOAuthFilePath } from './hahaOpenAIOAuthService.js'
@@ -28,8 +29,10 @@ const openAIModels: SavedProvider['models'] = {
 }
 
 const modelContextWindows = Object.fromEntries(
-  Object.values(openAIModels)
-    .map((model) => [model, getOpenAIContextWindowForModel(model)] as const)
+  OPENAI_CODEX_MODEL_CATALOG.map(
+    ({ value }) =>
+      [value, getOpenAICodexContextWindowForModel(value)] as const,
+  )
     .filter((entry): entry is readonly [string, number] => entry[1] !== null),
 )
 
diff --git a/src/services/compact/autoCompact.test.ts b/src/services/compact/autoCompact.test.ts
index e4c5853e..913f4ade 100644
--- a/src/services/compact/autoCompact.test.ts
+++ b/src/services/compact/autoCompact.test.ts
@@ -36,6 +36,13 @@ describe('model context window resolution', () => {
     expect(getContextWindowForModel('glm-4.5-air')).toBe(128_000)
   })
 
+  test('uses Codex OAuth effective context windows for OpenAI GPT models', () => {
+    expect(getContextWindowForModel('gpt-5.5')).toBe(258_400)
+    expect(getContextWindowForModel('gpt-5.4')).toBe(950_000)
+    expect(getContextWindowForModel('gpt-5.4-mini')).toBe(258_400)
+    expect(getContextWindowForModel('gpt-5.3-codex-spark')).toBe(121_600)
+  })
+
   test('uses per-model provider overrides before built-in defaults', () => {
     process.env[MODEL_CONTEXT_WINDOWS_ENV_KEY] = JSON.stringify({
       'deepseek-v4-pro': 500_000,
diff --git a/src/services/openaiAuth/models.test.ts b/src/services/openaiAuth/models.test.ts
index 284bf158..b8bcf9b6 100644
--- a/src/services/openaiAuth/models.test.ts
+++ b/src/services/openaiAuth/models.test.ts
@@ -1,9 +1,10 @@
 import { describe, expect, test } from 'bun:test'
 import {
+  OPENAI_CODEX_LARGE_EFFECTIVE_CONTEXT_WINDOW,
+  OPENAI_CODEX_SPARK_EFFECTIVE_CONTEXT_WINDOW,
+  OPENAI_CODEX_STANDARD_EFFECTIVE_CONTEXT_WINDOW,
   OPENAI_DEFAULT_MAIN_MODEL,
-  OPENAI_GPT5_LARGE_CONTEXT_WINDOW,
-  OPENAI_GPT5_STANDARD_CONTEXT_WINDOW,
-  getOpenAIContextWindowForModel,
+  getOpenAICodexContextWindowForModel,
   isOpenAIResponsesModel,
   resolveOpenAICodexModel,
 } from './models.js'
@@ -22,21 +23,21 @@ describe('openai auth model resolution', () => {
     expect(resolveOpenAICodexModel('opus')).toBe(OPENAI_DEFAULT_MAIN_MODEL)
   })
 
-  test('maps large-context GPT-5 models to a 1.05M context window', () => {
-    expect(getOpenAIContextWindowForModel('gpt-5.5')).toBe(
-      OPENAI_GPT5_LARGE_CONTEXT_WINDOW,
+  test('maps Codex OAuth GPT models to effective Codex context windows', () => {
+    expect(getOpenAICodexContextWindowForModel('gpt-5.5')).toBe(
+      OPENAI_CODEX_STANDARD_EFFECTIVE_CONTEXT_WINDOW,
     )
-    expect(getOpenAIContextWindowForModel('gpt-5.4')).toBe(
-      OPENAI_GPT5_LARGE_CONTEXT_WINDOW,
+    expect(getOpenAICodexContextWindowForModel('gpt-5.4')).toBe(
+      OPENAI_CODEX_LARGE_EFFECTIVE_CONTEXT_WINDOW,
     )
-  })
-
-  test('maps standard GPT-5 models to a 400k context window', () => {
-    expect(getOpenAIContextWindowForModel('gpt-5.3-codex')).toBe(
-      OPENAI_GPT5_STANDARD_CONTEXT_WINDOW,
+    expect(getOpenAICodexContextWindowForModel('gpt-5.3-codex')).toBe(
+      OPENAI_CODEX_STANDARD_EFFECTIVE_CONTEXT_WINDOW,
     )
-    expect(getOpenAIContextWindowForModel('gpt-5.4-mini')).toBe(
-      OPENAI_GPT5_STANDARD_CONTEXT_WINDOW,
+    expect(getOpenAICodexContextWindowForModel('gpt-5.4-mini')).toBe(
+      OPENAI_CODEX_STANDARD_EFFECTIVE_CONTEXT_WINDOW,
+    )
+    expect(getOpenAICodexContextWindowForModel('gpt-5.3-codex-spark')).toBe(
+      OPENAI_CODEX_SPARK_EFFECTIVE_CONTEXT_WINDOW,
     )
   })
 })
diff --git a/src/services/openaiAuth/models.ts b/src/services/openaiAuth/models.ts
index b5ed2505..1222d6dd 100644
--- a/src/services/openaiAuth/models.ts
+++ b/src/services/openaiAuth/models.ts
@@ -1,8 +1,22 @@
 export const OPENAI_DEFAULT_MAIN_MODEL = 'gpt-5.3-codex'
 export const OPENAI_DEFAULT_SONNET_MODEL = 'gpt-5.4'
 export const OPENAI_DEFAULT_HAIKU_MODEL = 'gpt-5.4-mini'
-export const OPENAI_GPT5_STANDARD_CONTEXT_WINDOW = 400_000
-export const OPENAI_GPT5_LARGE_CONTEXT_WINDOW = 1_050_000
+export const OPENAI_CODEX_EFFECTIVE_CONTEXT_PERCENT = 95
+export const OPENAI_CODEX_STANDARD_CONTEXT_WINDOW = 272_000
+export const OPENAI_CODEX_LARGE_CONTEXT_WINDOW = 1_000_000
+export const OPENAI_CODEX_SPARK_CONTEXT_WINDOW = 128_000
+export const OPENAI_CODEX_STANDARD_EFFECTIVE_CONTEXT_WINDOW = Math.floor(
+  (OPENAI_CODEX_STANDARD_CONTEXT_WINDOW * OPENAI_CODEX_EFFECTIVE_CONTEXT_PERCENT) /
+    100,
+)
+export const OPENAI_CODEX_LARGE_EFFECTIVE_CONTEXT_WINDOW = Math.floor(
+  (OPENAI_CODEX_LARGE_CONTEXT_WINDOW * OPENAI_CODEX_EFFECTIVE_CONTEXT_PERCENT) /
+    100,
+)
+export const OPENAI_CODEX_SPARK_EFFECTIVE_CONTEXT_WINDOW = Math.floor(
+  (OPENAI_CODEX_SPARK_CONTEXT_WINDOW * OPENAI_CODEX_EFFECTIVE_CONTEXT_PERCENT) /
+    100,
+)
 
 export type OpenAIModelCatalogEntry = {
   value: string
@@ -80,6 +94,8 @@ export function getOpenAIModelDisplayName(model: string): string | null {
   switch (model.trim().toLowerCase()) {
     case 'gpt-5.3-codex':
       return 'GPT-5.3 Codex'
+    case 'gpt-5.3-codex-spark':
+      return 'GPT-5.3 Codex Spark'
     case 'gpt-5.5':
       return 'GPT-5.5'
     case 'gpt-5.4':
@@ -101,21 +117,28 @@ export function getOpenAIModelDisplayName(model: string): string | null {
   }
 }
 
-export function getOpenAIContextWindowForModel(model: string): number | null {
+export function getOpenAICodexContextWindowForModel(
+  model: string,
+): number | null {
   const normalized = model.trim().toLowerCase()
 
-  // Current OpenAI model docs split GPT-5-family context windows into
-  // standard 400k models and larger 1.05M models.
+  // Codex OAuth follows the Codex app model catalog, not the public API model
+  // context limits. The catalog applies effective_context_window_percent=95,
+  // and the runtime /context display reports this effective window.
   if (
-    normalized === 'gpt-5.5' ||
-    normalized === 'gpt-5.5-pro' ||
     normalized === 'gpt-5.4' ||
     normalized === 'gpt-5.4-pro'
   ) {
-    return OPENAI_GPT5_LARGE_CONTEXT_WINDOW
+    return OPENAI_CODEX_LARGE_EFFECTIVE_CONTEXT_WINDOW
+  }
+
+  if (normalized === 'gpt-5.3-codex-spark') {
+    return OPENAI_CODEX_SPARK_EFFECTIVE_CONTEXT_WINDOW
   }
 
   if (
+    normalized === 'gpt-5.5' ||
+    normalized === 'gpt-5.5-pro' ||
     normalized === 'gpt-5.4-mini' ||
     normalized === 'gpt-5.4-nano' ||
     normalized === 'gpt-5.3-codex' ||
@@ -130,8 +153,11 @@ export function getOpenAIContextWindowForModel(model: string): number | null {
     normalized === 'gpt-5-mini' ||
     normalized === 'gpt-5-nano'
   ) {
-    return OPENAI_GPT5_STANDARD_CONTEXT_WINDOW
+    return OPENAI_CODEX_STANDARD_EFFECTIVE_CONTEXT_WINDOW
   }
 
   return null
 }
+
+export const getOpenAIContextWindowForModel =
+  getOpenAICodexContextWindowForModel
diff --git a/src/utils/context.ts b/src/utils/context.ts
index 8da26ad3..37045ed2 100644
--- a/src/utils/context.ts
+++ b/src/utils/context.ts
@@ -1,6 +1,6 @@
 // biome-ignore-all assist/source/organizeImports: ANT-ONLY import markers must not be reordered
 import { CONTEXT_1M_BETA_HEADER } from '../constants/betas.js'
-import { getOpenAIContextWindowForModel } from '../services/openaiAuth/models.js'
+import { getOpenAICodexContextWindowForModel } from '../services/openaiAuth/models.js'
 import { getGlobalConfig } from './config.js'
 import { isEnvTruthy } from './envUtils.js'
 import { getCanonicalName } from './model/model.js'
@@ -84,7 +84,7 @@ export function getContextWindowForModel(
     return configuredWindow
   }
 
-  const openAIContextWindow = getOpenAIContextWindowForModel(model)
+  const openAIContextWindow = getOpenAICodexContextWindowForModel(model)
   if (openAIContextWindow) {
     return openAIContextWindow
   }