diff --git a/src/services/api/codexShim.test.ts b/src/services/api/codexShim.test.ts
index 7589311a..387660dc 100644
--- a/src/services/api/codexShim.test.ts
+++ b/src/services/api/codexShim.test.ts
@@ -88,7 +88,7 @@ describe('Codex provider config', () => {
 
     const resolved = resolveProviderRequest({ model: 'codexplan' })
     expect(resolved.transport).toBe('codex_responses')
-    expect(resolved.resolvedModel).toBe('gpt-5.4')
+    expect(resolved.resolvedModel).toBe('gpt-5.5')
     expect(resolved.reasoning).toEqual({ effort: 'high' })
     expect(resolved.baseUrl).toBe('https://chatgpt.com/backend-api/codex')
   })
@@ -114,7 +114,7 @@ describe('Codex provider config', () => {
 
     expect(resolved.transport).toBe('chat_completions')
     expect(resolved.baseUrl).toBe('http://127.0.0.1:8080/v1')
-    expect(resolved.resolvedModel).toBe('gpt-5.4')
+    expect(resolved.resolvedModel).toBe('gpt-5.5')
   })
 
   test('resolves codexplan to Codex transport even when OPENAI_BASE_URL is the string "undefined"', async () => {
@@ -161,7 +161,7 @@ describe('Codex provider config', () => {
     const resolved = resolveProviderRequest()
     expect(resolved.transport).toBe('codex_responses')
     expect(resolved.baseUrl).toBe('https://chatgpt.com/backend-api/codex')
-    expect(resolved.resolvedModel).toBe('gpt-5.4')
+    expect(resolved.resolvedModel).toBe('gpt-5.5')
   })
 
   test('does not override custom base URL for codexplan (e.g., local provider)', async () => {
diff --git a/src/services/api/providerConfig.ts b/src/services/api/providerConfig.ts
index 27d55cfa..9d6c5ca0 100644
--- a/src/services/api/providerConfig.ts
+++ b/src/services/api/providerConfig.ts
@@ -31,7 +31,11 @@ const CODEX_ALIAS_MODELS: Record<
   }
 > = {
   codexplan: {
-    model: 'gpt-5.4',
+    model: 'gpt-5.5',
+    reasoningEffort: 'high',
+  },
+  'gpt-5.5': {
+    model: 'gpt-5.5',
     reasoningEffort: 'high',
   },
   'gpt-5.4': {
@@ -59,6 +63,10 @@ const CODEX_ALIAS_MODELS: Record<
   'gpt-5.1-codex-mini': {
     model: 'gpt-5.1-codex-mini',
   },
+  'gpt-5.5-mini': {
+    model: 'gpt-5.5-mini',
+    reasoningEffort: 'medium',
+  },
   'gpt-5.4-mini': {
     model: 'gpt-5.4-mini',
     reasoningEffort: 'medium',
diff --git a/src/utils/model/configs.ts b/src/utils/model/configs.ts
index fffb46e7..91a97e58 100644
--- a/src/utils/model/configs.ts
+++ b/src/utils/model/configs.ts
@@ -36,7 +36,7 @@ export const CLAUDE_3_7_SONNET_CONFIG = {
   openai: 'gpt-4o-mini',
   gemini: 'gemini-2.0-flash',
   github: 'github:copilot',
-  codex: 'gpt-5.4',
+  codex: 'gpt-5.5',
   'nvidia-nim': 'nvidia/llama-3.1-nemotron-70b-instruct',
   minimax: 'MiniMax-M2.5',
 } as const satisfies ModelConfig
@@ -49,7 +49,7 @@ export const CLAUDE_3_5_V2_SONNET_CONFIG = {
   openai: 'gpt-4o-mini',
   gemini: 'gemini-2.0-flash',
   github: 'github:copilot',
-  codex: 'gpt-5.4',
+  codex: 'gpt-5.5',
   'nvidia-nim': 'nvidia/llama-3.1-nemotron-70b-instruct',
   minimax: 'MiniMax-M2.5',
 } as const satisfies ModelConfig
@@ -62,7 +62,7 @@ export const CLAUDE_3_5_HAIKU_CONFIG = {
   openai: 'gpt-4o-mini',
   gemini: 'gemini-2.0-flash-lite',
   github: 'github:copilot',
-  codex: 'gpt-5.4',
+  codex: 'gpt-5.5',
   'nvidia-nim': 'nvidia/llama-3.1-nemotron-70b-instruct',
   minimax: 'MiniMax-M2.5',
 } as const satisfies ModelConfig
@@ -75,7 +75,7 @@ export const CLAUDE_HAIKU_4_5_CONFIG = {
   openai: 'gpt-4o-mini',
   gemini: 'gemini-2.0-flash-lite',
   github: 'github:copilot',
-  codex: 'gpt-5.4',
+  codex: 'gpt-5.5',
   'nvidia-nim': 'nvidia/llama-3.1-nemotron-70b-instruct',
   minimax: 'MiniMax-M2.5',
 } as const satisfies ModelConfig
@@ -88,7 +88,7 @@ export const CLAUDE_SONNET_4_CONFIG = {
   openai: 'gpt-4o-mini',
   gemini: 'gemini-2.0-flash',
   github: 'github:copilot',
-  codex: 'gpt-5.4',
+  codex: 'gpt-5.5',
   'nvidia-nim': 'nvidia/llama-3.1-nemotron-70b-instruct',
   minimax: 'MiniMax-M2.5',
 } as const satisfies ModelConfig
@@ -101,7 +101,7 @@ export const CLAUDE_SONNET_4_5_CONFIG = {
   openai: 'gpt-4o',
   gemini: 'gemini-2.0-flash',
   github: 'github:copilot',
-  codex: 'gpt-5.4',
+  codex: 'gpt-5.5',
   'nvidia-nim': 'nvidia/llama-3.1-nemotron-70b-instruct',
   minimax: 'MiniMax-M2.5',
 } as const satisfies ModelConfig
@@ -114,7 +114,7 @@ export const CLAUDE_OPUS_4_CONFIG = {
   openai: 'gpt-4o',
   gemini: 'gemini-2.5-pro',
   github: 'github:copilot',
-  codex: 'gpt-5.4',
+  codex: 'gpt-5.5',
   'nvidia-nim': 'nvidia/llama-3.1-nemotron-70b-instruct',
   minimax: 'MiniMax-M2.5',
 } as const satisfies ModelConfig
@@ -127,7 +127,7 @@ export const CLAUDE_OPUS_4_1_CONFIG = {
   openai: 'gpt-4o',
   gemini: 'gemini-2.5-pro',
   github: 'github:copilot',
-  codex: 'gpt-5.4',
+  codex: 'gpt-5.5',
   'nvidia-nim': 'nvidia/llama-3.1-nemotron-70b-instruct',
   minimax: 'MiniMax-M2.5',
 } as const satisfies ModelConfig
@@ -140,7 +140,7 @@ export const CLAUDE_OPUS_4_5_CONFIG = {
   openai: 'gpt-4o',
   gemini: 'gemini-2.5-pro',
   github: 'github:copilot',
-  codex: 'gpt-5.4',
+  codex: 'gpt-5.5',
   'nvidia-nim': 'nvidia/llama-3.1-nemotron-70b-instruct',
   minimax: 'MiniMax-M2.5',
 } as const satisfies ModelConfig
@@ -153,7 +153,7 @@ export const CLAUDE_OPUS_4_6_CONFIG = {
   openai: 'gpt-4o',
   gemini: 'gemini-2.5-pro',
   github: 'github:copilot',
-  codex: 'gpt-5.4',
+  codex: 'gpt-5.5',
   'nvidia-nim': 'nvidia/llama-3.1-nemotron-70b-instruct',
   minimax: 'MiniMax-M2.5',
 } as const satisfies ModelConfig
@@ -166,7 +166,7 @@ export const CLAUDE_SONNET_4_6_CONFIG = {
   openai: 'gpt-4o',
   gemini: 'gemini-2.0-flash',
   github: 'github:copilot',
-  codex: 'gpt-5.4',
+  codex: 'gpt-5.5',
   'nvidia-nim': 'nvidia/llama-3.1-nemotron-70b-instruct',
   minimax: 'MiniMax-M2.5',
 } as const satisfies ModelConfig
diff --git a/src/utils/model/copilotModels.ts b/src/utils/model/copilotModels.ts
index cd3204bd..51f039c5 100644
--- a/src/utils/model/copilotModels.ts
+++ b/src/utils/model/copilotModels.ts
@@ -32,6 +32,38 @@ export type CopilotModel = {
 }
 
 export const COPILOT_MODELS: Record<string, CopilotModel> = {
+  'gpt-5.5': {
+    id: 'gpt-5.5',
+    name: 'GPT-5.5',
+    family: 'gpt',
+    attachment: false,
+    reasoning: true,
+    tool_call: true,
+    temperature: true,
+    knowledge: '2025-05',
+    release_date: '2025-05-01',
+    last_updated: '2025-05-01',
+    modalities: { input: ['text'], output: ['text'] },
+    open_weights: false,
+    cost: { input: 0, output: 0 },
+    limit: { context: 400000, output: 32768 },
+  },
+  'gpt-5.5-mini': {
+    id: 'gpt-5.5-mini',
+    name: 'GPT-5.5 mini',
+    family: 'gpt-mini',
+    attachment: false,
+    reasoning: true,
+    tool_call: true,
+    temperature: true,
+    knowledge: '2025-05',
+    release_date: '2025-05-01',
+    last_updated: '2025-05-01',
+    modalities: { input: ['text'], output: ['text'] },
+    open_weights: false,
+    cost: { input: 0, output: 0 },
+    limit: { context: 400000, output: 32768 },
+  },
   'gpt-5.4': {
     id: 'gpt-5.4',
     name: 'GPT-5.4',
diff --git a/src/utils/model/model.ts b/src/utils/model/model.ts
index f5a7607b..d19bde76 100644
--- a/src/utils/model/model.ts
+++ b/src/utils/model/model.ts
@@ -178,9 +178,9 @@ export function getDefaultOpusModel(): ModelName {
   if (getAPIProvider() === 'openai') {
     return process.env.OPENAI_MODEL || 'gpt-4o'
   }
-  // Codex provider: use user-specified model or default to gpt-5.4
+  // Codex provider: use user-specified model or default to gpt-5.5
   if (getAPIProvider() === 'codex') {
-    return process.env.OPENAI_MODEL || 'gpt-5.4'
+    return process.env.OPENAI_MODEL || 'gpt-5.5'
   }
   // GitHub Copilot provider
   if (getAPIProvider() === 'github') {
@@ -222,7 +222,7 @@ export function getDefaultSonnetModel(): ModelName {
   }
   // Codex provider
   if (getAPIProvider() === 'codex') {
-    return process.env.OPENAI_MODEL || 'gpt-5.4'
+    return process.env.OPENAI_MODEL || 'gpt-5.5'
   }
   // GitHub Copilot provider
   if (getAPIProvider() === 'github') {
@@ -258,7 +258,7 @@ export function getDefaultHaikuModel(): ModelName {
   }
   // Codex provider
   if (getAPIProvider() === 'codex') {
-    return process.env.OPENAI_MODEL || 'gpt-5.4'
+    return process.env.OPENAI_MODEL || 'gpt-5.5'
   }
   // GitHub Copilot provider
   if (getAPIProvider() === 'github') {
@@ -340,9 +340,9 @@ export function getDefaultMainLoopModelSetting(): ModelName | ModelAlias {
   if (getAPIProvider() === 'openai') {
     return process.env.OPENAI_MODEL || 'gpt-4o'
   }
-  // Codex provider: always use the configured Codex model (default gpt-5.4)
+  // Codex provider: always use the configured Codex model (default gpt-5.5)
   if (getAPIProvider() === 'codex') {
-    return process.env.OPENAI_MODEL || 'gpt-5.4'
+    return process.env.OPENAI_MODEL || 'gpt-5.5'
   }
 
   // Ants default to defaultModel from flag config, or Opus 1M if not configured
@@ -506,7 +506,7 @@ export function renderModelSetting(setting: ModelName | ModelAlias): string {
   }
   // Handle Codex models - show actual model name + resolved model
   if (setting === 'codexplan') {
-    return 'codexplan (gpt-5.4)'
+    return 'codexplan (gpt-5.5)'
   }
   if (setting === 'codexspark') {
     return 'codexspark (gpt-5.3-codex-spark)'
@@ -527,6 +527,8 @@ export function getPublicModelDisplayName(model: ModelName): string | null {
   if (getAPIProvider() === 'openai' || getAPIProvider() === 'gemini' || getAPIProvider() === 'codex' || getAPIProvider() === 'github') {
     // Return display names for known GitHub Copilot models
     const copilotModelNames: Record<string, string> = {
+      'gpt-5.5': 'GPT-5.5',
+      'gpt-5.5-mini': 'GPT-5.5 mini',
       'gpt-5.4': 'GPT-5.4',
       'gpt-5.4-mini': 'GPT-5.4 mini',
       'gpt-5.3-codex': 'GPT-5.3 Codex',
@@ -553,6 +555,8 @@ export function getPublicModelDisplayName(model: ModelName): string | null {
     return null
   }
   switch (model) {
+    case 'gpt-5.5':
+      return 'GPT-5.5'
     case 'gpt-5.4':
       return 'GPT-5.4'
     case 'gpt-5.3-codex-spark':
@@ -687,7 +691,7 @@ export function parseUserSpecifiedModel(
 
   // Handle Codex aliases - map to actual model names
   if (modelString === 'codexplan') {
-    return 'gpt-5.4'
+    return 'gpt-5.5'
   }
   if (modelString === 'codexspark') {
     return 'gpt-5.3-codex-spark'
diff --git a/src/utils/model/modelOptions.ts b/src/utils/model/modelOptions.ts
index c9e35167..b2cc785a 100644
--- a/src/utils/model/modelOptions.ts
+++ b/src/utils/model/modelOptions.ts
@@ -297,9 +297,9 @@ function getOpusPlanOption(): ModelOption {
 
 function getCodexPlanOption(): ModelOption {
   return {
-    value: 'gpt-5.4',
-    label: 'gpt-5.4',
-    description: 'GPT-5.4 on the Codex backend with high reasoning',
+    value: 'gpt-5.5',
+    label: 'gpt-5.5',
+    description: 'GPT-5.5 on the Codex backend with high reasoning',
   }
 }
 
@@ -313,6 +313,11 @@ function getCodexSparkOption(): ModelOption {
 
 function getCodexModelOptions(): ModelOption[] {
   return [
+    {
+      value: 'gpt-5.5',
+      label: 'gpt-5.5',
+      description: 'GPT-5.5 with high reasoning',
+    },
     {
       value: 'gpt-5.4',
       label: 'gpt-5.4',
@@ -348,6 +353,11 @@ function getCodexModelOptions(): ModelOption[] {
       label: 'gpt-5.1-codex-mini',
       description: 'GPT-5.1 Codex Mini - faster, cheaper',
     },
+    {
+      value: 'gpt-5.5-mini',
+      label: 'gpt-5.5-mini',
+      description: 'GPT-5.5 Mini - faster, cheaper',
+    },
     {
       value: 'gpt-5.4-mini',
       label: 'gpt-5.4-mini',
@@ -679,7 +689,7 @@ export function getModelOptions(fastMode = false): ModelOption[] {
     return filterModelOptionsByAllowlist(options)
   } else if (customModel === 'opusplan') {
     return filterModelOptionsByAllowlist([...options, getOpusPlanOption()])
-  } else if (customModel === 'gpt-5.4') {
+  } else if (customModel === 'gpt-5.5') {
     return filterModelOptionsByAllowlist([...options, getCodexPlanOption()])
   } else if (customModel === 'gpt-5.3-codex-spark') {
     return filterModelOptionsByAllowlist([...options, getCodexSparkOption()])
diff --git a/src/utils/model/openaiContextWindows.ts b/src/utils/model/openaiContextWindows.ts
index 20cf5e4c..7de2a6e7 100644
--- a/src/utils/model/openaiContextWindows.ts
+++ b/src/utils/model/openaiContextWindows.ts
@@ -38,6 +38,8 @@ const OPENAI_CONTEXT_WINDOWS: Record<string, number> = {
   'github:copilot:gpt-5.2':                  400_000,
   'github:copilot:gpt-5.2-codex':            400_000,
   'github:copilot:gpt-5.3-codex':            400_000,
+  'github:copilot:gpt-5.5':                  400_000,
+  'github:copilot:gpt-5.5-mini':             400_000,
   'github:copilot:gpt-5.4':                  400_000,
   'github:copilot:gpt-5.4-mini':             400_000,
   // Gemini
@@ -60,6 +62,8 @@ const OPENAI_CONTEXT_WINDOWS: Record<string, number> = {
   'github_copilot/gpt-4.1':                  128_000,
   'github_copilot/gpt-4o':                   128_000,
   'github_copilot/gpt-5-mini':               264_000,
+  'github_copilot/gpt-5.5':                  400_000,
+  'github_copilot/gpt-5.5-mini':             400_000,
   'github_copilot/gpt-5.4':                  400_000,
   'github_copilot/gpt-5.4-mini':             400_000,
   'github_copilot/gemini-2.5-pro':           128_000,
@@ -71,6 +75,9 @@ const OPENAI_CONTEXT_WINDOWS: Record<string, number> = {
   // limits for the same model name, so we cannot safely hardcode values here.
 
   // OpenAI
+  'gpt-5.5':               1_050_000,
+  'gpt-5.5-mini':            400_000,
+  'gpt-5.5-nano':            400_000,
   'gpt-5.4':               1_050_000,
   'gpt-5.4-mini':            400_000,
   'gpt-5.4-nano':            400_000,
@@ -288,6 +295,9 @@ const OPENAI_MAX_OUTPUT_TOKENS: Record<string, number> = {
   // NOTE: bare Claude model names omitted — see context windows comment above.
 
   // OpenAI
+  'gpt-5.5':                 128_000,
+  'gpt-5.5-mini':            128_000,
+  'gpt-5.5-nano':            128_000,
   'gpt-5.4':                 128_000,
   'gpt-5.4-mini':            128_000,
   'gpt-5.4-nano':            128_000,
diff --git a/src/utils/providerProfiles.ts b/src/utils/providerProfiles.ts
index 6da78329..eeca893d 100644
--- a/src/utils/providerProfiles.ts
+++ b/src/utils/providerProfiles.ts
@@ -153,7 +153,7 @@ export function getProviderPresetDefaults(
         provider: 'openai',
         name: 'OpenAI',
         baseUrl: 'https://api.openai.com/v1',
-        model: 'gpt-5.3-codex',
+        model: 'gpt-5.4',
         apiKey: '',
         requiresApiKey: true,
       }