diff --git a/config/base-codex.settings.json b/config/base-codex.settings.json
index b64fe8a4..fbf1314a 100644
--- a/config/base-codex.settings.json
+++ b/config/base-codex.settings.json
@@ -4,7 +4,7 @@
     "ANTHROPIC_AUTH_TOKEN": "ccs-internal-managed",
     "ANTHROPIC_MODEL": "gpt-5.3-codex",
     "ANTHROPIC_DEFAULT_OPUS_MODEL": "gpt-5.3-codex",
-    "ANTHROPIC_DEFAULT_SONNET_MODEL": "gpt-5.3-codex",
-    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "gpt-5.3-codex"
+    "ANTHROPIC_DEFAULT_SONNET_MODEL": "gpt-5.3-codex-high",
+    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "gpt-5-mini"
   }
 }
diff --git a/src/cliproxy/model-config.ts b/src/cliproxy/model-config.ts
index 1442a93a..8e1644a2 100644
--- a/src/cliproxy/model-config.ts
+++ b/src/cliproxy/model-config.ts
@@ -142,6 +142,10 @@ export async function configureProviderModel(
 
   // Get base env vars for defaults
   const baseEnv = getClaudeEnvVars(provider);
+  const codexSonnetModel =
+    provider === 'codex' && !selectedModel.match(/-(xhigh|high|medium)$/)
+      ? `${selectedModel}-high`
+      : selectedModel;
 
   // Read existing settings to preserve user customizations
   let existingSettings: Record<string, unknown> = {};
@@ -165,7 +169,7 @@ export async function configureProviderModel(
     ANTHROPIC_AUTH_TOKEN: baseEnv.ANTHROPIC_AUTH_TOKEN || '',
     ANTHROPIC_MODEL: selectedModel,
     ANTHROPIC_DEFAULT_OPUS_MODEL: selectedModel,
-    ANTHROPIC_DEFAULT_SONNET_MODEL: selectedModel,
+    ANTHROPIC_DEFAULT_SONNET_MODEL: codexSonnetModel,
     ANTHROPIC_DEFAULT_HAIKU_MODEL: baseEnv.ANTHROPIC_DEFAULT_HAIKU_MODEL || '',
   };
 
diff --git a/src/cliproxy/services/variant-settings.ts b/src/cliproxy/services/variant-settings.ts
index 211ff95c..3dd93b4d 100644
--- a/src/cliproxy/services/variant-settings.ts
+++ b/src/cliproxy/services/variant-settings.ts
@@ -44,13 +44,15 @@ function buildSettingsEnv(
   port: number = CLIPROXY_DEFAULT_PORT
 ): SettingsEnv {
   const baseEnv = getClaudeEnvVars(provider as CLIProxyProvider, port);
+  const codexSonnetModel =
+    provider === 'codex' && !model.match(/-(xhigh|high|medium)$/) ? `${model}-high` : model;
 
   return {
     ANTHROPIC_BASE_URL: baseEnv.ANTHROPIC_BASE_URL || '',
     ANTHROPIC_AUTH_TOKEN: baseEnv.ANTHROPIC_AUTH_TOKEN || '',
     ANTHROPIC_MODEL: model,
     ANTHROPIC_DEFAULT_OPUS_MODEL: model,
-    ANTHROPIC_DEFAULT_SONNET_MODEL: model,
+    ANTHROPIC_DEFAULT_SONNET_MODEL: codexSonnetModel,
     ANTHROPIC_DEFAULT_HAIKU_MODEL: baseEnv.ANTHROPIC_DEFAULT_HAIKU_MODEL || model,
   };
 }
diff --git a/ui/src/lib/model-catalogs.ts b/ui/src/lib/model-catalogs.ts
index 9d31f3bb..2559cffe 100644
--- a/ui/src/lib/model-catalogs.ts
+++ b/ui/src/lib/model-catalogs.ts
@@ -142,7 +142,7 @@ export const MODEL_CATALOGS: Record<string, ProviderCatalog> = {
         presetMapping: {
           default: 'gpt-5.3-codex',
           opus: 'gpt-5.3-codex',
-          sonnet: 'gpt-5.3-codex',
+          sonnet: 'gpt-5.3-codex-high',
           haiku: 'gpt-5-mini',
         },
       },
@@ -153,7 +153,7 @@ export const MODEL_CATALOGS: Record<string, ProviderCatalog> = {
         presetMapping: {
           default: 'gpt-5.2-codex',
           opus: 'gpt-5.2-codex',
-          sonnet: 'gpt-5.2-codex',
+          sonnet: 'gpt-5.2-codex-high',
           haiku: 'gpt-5-mini',
         },
       },