diff --git a/src/main/text-generation/commit-message-text-generation-settings.test.ts b/src/main/text-generation/commit-message-text-generation-settings.test.ts
index b7640a33d72..e40514409bc 100644
--- a/src/main/text-generation/commit-message-text-generation-settings.test.ts
+++ b/src/main/text-generation/commit-message-text-generation-settings.test.ts
@@ -27,7 +27,7 @@ describe('resolveCommitMessageSettings', () => {
       ok: true,
       params: {
         agentId: 'codex',
-        model: 'gpt-5.5',
+        model: 'gpt-5.6-terra',
         thinkingLevel: 'low',
         customPrompt: 'Use Conventional Commits.',
         commandInputTemplate: '{basePrompt}\n\nUse Conventional Commits.'
@@ -69,7 +69,7 @@ describe('resolveCommitMessageSettings', () => {
       ok: true,
       params: {
         agentId: 'codex',
-        model: 'gpt-5.5',
+        model: 'gpt-5.6-terra',
         thinkingLevel: 'low'
       }
     })
diff --git a/src/shared/commit-message-agent-spec.test.ts b/src/shared/commit-message-agent-spec.test.ts
index 68d1ffc79bc..18635420b4c 100644
--- a/src/shared/commit-message-agent-spec.test.ts
+++ b/src/shared/commit-message-agent-spec.test.ts
@@ -45,9 +45,10 @@ describe('COMMIT_MESSAGE_AGENT_SPECS', () => {
     ])
   })
 
-  it('uses the strongest available defaults for core agents', () => {
+  it('uses the expected defaults for core agents', () => {
     expect(COMMIT_MESSAGE_AGENT_SPECS.claude?.defaultModelId).toBe('sonnet')
-    expect(COMMIT_MESSAGE_AGENT_SPECS.codex?.defaultModelId).toBe('gpt-5.5')
+    expect(COMMIT_MESSAGE_AGENT_SPECS.codex?.defaultModelId).toBe('gpt-5.6-terra')
+    expect(getCommitMessageModel('codex', 'gpt-5.6-terra')?.defaultThinkingLevel).toBe('low')
     expect(COMMIT_MESSAGE_AGENT_SPECS.pi?.defaultModelId).toBe('default')
   })
 
@@ -189,6 +190,7 @@ describe('COMMIT_MESSAGE_AGENT_SPECS', () => {
   it('orders Codex models by version descending to match the official picker', () => {
     const ids = COMMIT_MESSAGE_AGENT_SPECS.codex?.models.map((m) => m.id)
     expect(ids).toEqual([
+      'gpt-5.6-terra',
       'gpt-5.5',
       'gpt-5.4',
       'gpt-5.4-mini',
@@ -206,7 +208,7 @@ describe('COMMIT_MESSAGE_AGENT_SPECS', () => {
       id: 'codex',
       label: 'Codex',
       modelSource: 'dynamic',
-      defaultModelId: 'gpt-5.5'
+      defaultModelId: 'gpt-5.6-terra'
     })
     expect(codex).not.toHaveProperty('binary')
     expect(codex).not.toHaveProperty('buildArgs')
diff --git a/src/shared/commit-message-agent-specs-primary.ts b/src/shared/commit-message-agent-specs-primary.ts
index ce7b35afcfb..7a2aa70c979 100644
--- a/src/shared/commit-message-agent-specs-primary.ts
+++ b/src/shared/commit-message-agent-specs-primary.ts
@@ -109,6 +109,12 @@ export function buildPrimaryCommitMessageAgentSpecs({
       // Why: ordered to match the official `codex` model picker — descending
       // by version so the frontier model lands on top and legacy models trail.
       models: [
+        {
+          id: 'gpt-5.6-terra',
+          label: 'GPT-5.6 Terra',
+          thinkingLevels: OPENAI_THINKING_LEVELS,
+          defaultThinkingLevel: 'low'
+        },
         {
           id: 'gpt-5.5',
           label: 'GPT-5.5',
@@ -150,7 +156,7 @@ export function buildPrimaryCommitMessageAgentSpecs({
           defaultThinkingLevel: 'low'
         }
       ],
-      defaultModelId: 'gpt-5.5'
+      defaultModelId: 'gpt-5.6-terra'
     },
     opencode: {
       id: 'opencode',
diff --git a/src/shared/source-control-ai-policy-regression.test.ts b/src/shared/source-control-ai-policy-regression.test.ts
index c8cb6bd75ab..49261e68bf0 100644
--- a/src/shared/source-control-ai-policy-regression.test.ts
+++ b/src/shared/source-control-ai-policy-regression.test.ts
@@ -21,7 +21,7 @@ describe('source-control AI policy regressions', () => {
 
     expect(result).toMatchObject({
       ok: true,
-      value: { params: { agentId: 'codex', model: 'gpt-5.5' } }
+      value: { params: { agentId: 'codex', model: 'gpt-5.6-terra' } }
     })
   })