diff --git a/internal/registry/model_definitions.go b/internal/registry/model_definitions.go
index abd943bc..19f53e5c 100644
--- a/internal/registry/model_definitions.go
+++ b/internal/registry/model_definitions.go
@@ -258,6 +258,19 @@ func GetGitHubCopilotModels() []*ModelInfo {
 			SupportedEndpoints:  []string{"/responses"},
 			Thinking:            &ThinkingSupport{Levels: []string{"none", "low", "medium", "high", "xhigh"}},
 		},
+		{
+			ID:                  "gpt-5.3-codex",
+			Object:              "model",
+			Created:             now,
+			OwnedBy:             "github-copilot",
+			Type:                "github-copilot",
+			DisplayName:         "GPT-5.3 Codex",
+			Description:         "OpenAI GPT-5.3 Codex via GitHub Copilot",
+			ContextLength:       200000,
+			MaxCompletionTokens: 32768,
+			SupportedEndpoints:  []string{"/responses"},
+			Thinking:            &ThinkingSupport{Levels: []string{"none", "low", "medium", "high", "xhigh"}},
+		},
 		{
 			ID:                  "claude-haiku-4.5",
 			Object:              "model",