fix: default api_type for specific github copilot models

pkg/model/provider/defaults.go

@@ -43,6 +43,11 @@ func isOpenAICompatibleProvider(providerType string) bool {
 	return exists && alias.APIType == "openai"
 }
 
+// isGithubCopilotProvider returns true if the provider type is "github-copilot".
+func isGithubCopilotProvider(providerType string) bool {
+	return providerType == "github-copilot"
+}
+
 // ---------------------------------------------------------------------------
 // Provider defaults
 // ---------------------------------------------------------------------------
@@ -191,6 +196,9 @@ func cloneModelConfig(cfg *latest.ModelConfig) *latest.ModelConfig {
 //
 // NOTE: max_tokens is NOT set here; see teamloader and runtime/model_switcher.
 func applyModelDefaults(cfg *latest.ModelConfig) {
+	// Set appropriate github copilot api_type.
+	applyGithubCopilotAPIType(cfg)
+
 	// Explicitly disabled → normalise to nil so providers never see it.
 	if cfg.ThinkingBudget.IsDisabled() {
 		cfg.ThinkingBudget = nil
@@ -239,6 +247,19 @@ func ensureInterleavedThinking(cfg *latest.ModelConfig, providerType string) {
 	}
 }
 
+func applyGithubCopilotAPIType(cfg *latest.ModelConfig) {
+	if isGithubCopilotProvider(cfg.Provider) && isCopilotResponsesModel(cfg.Model) {
+		if cfg.ProviderOpts == nil {
+			cfg.ProviderOpts = make(map[string]any)
+		}
+		// If it's not set, or was set to openai_chatcompletions by the generic fallback, override it.
+		// User explicit openai_chatcompletions is unsupported for these models.
+		if apiType, ok := cfg.ProviderOpts["api_type"].(string); !ok || apiType == "" || apiType == "openai_chatcompletions" {
+			cfg.ProviderOpts["api_type"] = "openai_responses"
+		}
+	}
+}
+
 // needsInterleavedThinking reports whether a (provider, model) pair refers to
 // a Claude model on a host that supports the interleaved-thinking beta.
 func needsInterleavedThinking(providerType, model string) bool {
@@ -250,3 +271,12 @@ func needsInterleavedThinking(providerType, model string) bool {
 	}
 	return false
 }
+
+// isCopilotResponsesModel returns true if the model is a GitHub Copilot model that requires the openai_responses API type.
+func isCopilotResponsesModel(model string) bool {
+	switch model {
+	case "gpt-5.3-codex", "gpt-5.2-codex", "gpt-5.4-mini", "gpt-5.4-nano":
+		return true
+	}
+	return false
+}

pkg/model/provider/model_defaults_test.go

@@ -13,12 +13,14 @@ func TestApplyModelDefaults(t *testing.T) {
 	t.Parallel()
 
 	boolPtr := func(v bool) *bool { return &v }
+	strPtr := func(v string) *string { return &v }
 
 	tests := []struct {
 		name            string
 		config          *latest.ModelConfig
 		wantBudget      *latest.ThinkingBudget // nil means no thinking
 		wantInterleaved *bool                  // nil means key must not exist
+		wantAPIType     *string                // nil means key must not exist
 	}{
 		// --- OpenAI: only o-series gets defaults ---
 		{
@@ -138,6 +140,28 @@ func TestApplyModelDefaults(t *testing.T) {
 			config: &latest.ModelConfig{Provider: "openai", Model: "gpt-4o", ThinkingBudget: &latest.ThinkingBudget{Effort: "none"}},
 		},
 
+		// --- GitHub Copilot: api_type defaults and overrides ---
+		{
+			name:        "github-copilot: responses model defaults to openai_responses",
+			config:      &latest.ModelConfig{Provider: "github-copilot", Model: "gpt-5.3-codex"},
+			wantAPIType: strPtr("openai_responses"),
+		},
+		{
+			name:        "github-copilot: responses model overrides openai_chatcompletions",
+			config:      &latest.ModelConfig{Provider: "github-copilot", Model: "gpt-5.3-codex", ProviderOpts: map[string]any{"api_type": "openai_chatcompletions"}},
+			wantAPIType: strPtr("openai_responses"),
+		},
+		{
+			name:        "github-copilot: responses model preserves explicit openai_responses",
+			config:      &latest.ModelConfig{Provider: "github-copilot", Model: "gpt-5.3-codex", ProviderOpts: map[string]any{"api_type": "openai_responses"}},
+			wantAPIType: strPtr("openai_responses"),
+		},
+		{
+			name:        "github-copilot: responses model preserves custom api_type",
+			config:      &latest.ModelConfig{Provider: "github-copilot", Model: "gpt-5.3-codex", ProviderOpts: map[string]any{"api_type": "custom_hypothetical_type"}},
+			wantAPIType: strPtr("custom_hypothetical_type"),
+		},
+
 		// --- Unknown / other providers: no effect ---
 		{
 			name:   "unknown provider: no effect",
@@ -173,6 +197,12 @@ func TestApplyModelDefaults(t *testing.T) {
 				require.NotNil(t, tt.config.ProviderOpts)
 				assert.Equal(t, *tt.wantInterleaved, tt.config.ProviderOpts["interleaved_thinking"])
 			}
+
+			// Check api_type if wantAPIType is specified.
+			if tt.wantAPIType != nil {
+				require.NotNil(t, tt.config.ProviderOpts)
+				assert.Equal(t, *tt.wantAPIType, tt.config.ProviderOpts["api_type"])
+			}
 		})
 	}
 }
@@ -265,6 +295,18 @@ func TestApplyProviderDefaults_DoesNotModifyOriginal(t *testing.T) {
 	assert.Equal(t, "original_value", original.ProviderOpts["custom_key"])
 }
 
+func TestIsCopilotResponsesModel(t *testing.T) {
+	t.Parallel()
+
+	assert.True(t, isCopilotResponsesModel("gpt-5.3-codex"))
+	assert.True(t, isCopilotResponsesModel("gpt-5.2-codex"))
+	assert.True(t, isCopilotResponsesModel("gpt-5.4-mini"))
+	assert.True(t, isCopilotResponsesModel("gpt-5.4-nano"))
+	assert.False(t, isCopilotResponsesModel("gpt-4o"))
+	assert.False(t, isCopilotResponsesModel("claude-sonnet-4-5"))
+	assert.False(t, isCopilotResponsesModel(""))
+}
+
 // TestApplyProviderDefaults_InheritsAuthFromProviderConfig verifies that a
 // ProviderConfig's Auth block is inherited by models that don't override it,
 // while a model-level Auth always wins.

pkg/model/provider/provider_defaults_test.go

@@ -414,3 +414,35 @@ func TestApplyProviderDefaults_AliasFallback(t *testing.T) {
 	assert.Empty(t, cfg.BaseURL)
 	assert.Empty(t, cfg.TokenKey)
 }
+
+func TestIsGithubCopilotProvider(t *testing.T) {
+	t.Parallel()
+
+	assert.True(t, isGithubCopilotProvider("github-copilot"))
+	assert.False(t, isGithubCopilotProvider("openai"))
+	assert.False(t, isGithubCopilotProvider(""))
+}
+
+func TestGithubCopilotApiType(t *testing.T) {
+	t.Parallel()
+
+	cfg := &latest.ModelConfig{
+		Provider: "github-copilot",
+		Model:    "gpt-5.3-codex",
+	}
+	enhancedCfg := applyProviderDefaults(cfg, nil)
+	apiType := resolveProviderType(enhancedCfg)
+
+	assert.Equal(t, "openai_responses", apiType)
+
+	// test when it is a custom provider
+	customProviders := map[string]latest.ProviderConfig{
+		"github-copilot": {
+			Provider: "github-copilot",
+		},
+	}
+	enhancedCfg2 := applyProviderDefaults(cfg, customProviders)
+	apiType2 := resolveProviderType(enhancedCfg2)
+
+	assert.Equal(t, "openai_responses", apiType2)
+}