diff --git a/pkg/model/provider/provider.go b/pkg/model/provider/provider.go
index 749bb9536..afc2f69b3 100644
--- a/pkg/model/provider/provider.go
+++ b/pkg/model/provider/provider.go
@@ -406,6 +406,9 @@ func applyProviderDefaults(cfg *latest.ModelConfig, customProviders map[string]l
 //
 // 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
@@ -467,6 +470,19 @@ func ensureInterleavedThinking(cfg *latest.ModelConfig, providerType string) {
 	}
 }
 
+// applyGithubCopilotAPIType ensures api_type is set to openai_responses for appropriate models.
+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.
+		if apiType, ok := cfg.ProviderOpts["api_type"].(string); !ok || apiType == "" || apiType == "openai_chatcompletions" {
+			cfg.ProviderOpts["api_type"] = "openai_responses"
+		}
+	}
+}
+
 // isOpenAIThinkingOnlyModel returns true for OpenAI models that require thinking
 // to function properly (o-series reasoning models).
 func isOpenAIThinkingOnlyModel(model string) bool {
@@ -529,6 +545,23 @@ func resolveEffectiveProvider(cfg latest.ProviderConfig) string {
 	return "openai"
 }
 
+func isGithubCopilotProvider(providerType string) bool {
+	switch providerType {
+	case "github-copilot":
+		return true
+	default:
+		return false
+	}
+}
+
+func isCopilotResponsesModel(model string) bool {
+	codex := map[string]bool{
+		"gpt-5.3-codex": true,
+		"gpt-5.2-codex": true,
+	}
+	return codex[model]
+}
+
 // isOpenAICompatibleProvider returns true if the provider type uses the OpenAI API protocol.
 func isOpenAICompatibleProvider(providerType string) bool {
 	switch providerType {
diff --git a/pkg/model/provider/provider_test.go b/pkg/model/provider/provider_test.go
index 2a678cb23..1e0ef51b7 100644
--- a/pkg/model/provider/provider_test.go
+++ b/pkg/model/provider/provider_test.go
@@ -4,6 +4,8 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+
+	"github.com/docker/docker-agent/pkg/config/latest"
 )
 
 func TestCatalogProviders(t *testing.T) {
@@ -88,3 +90,50 @@ func TestIsKnownProvider(t *testing.T) {
 	assert.False(t, IsKnownProvider("unknown"))
 	assert.False(t, IsKnownProvider(""))
 }
+
+func TestIsGithubCopilotProvider(t *testing.T) {
+	t.Parallel()
+
+	assert.True(t, isGithubCopilotProvider("github-copilot"))
+	assert.False(t, isGithubCopilotProvider("openai"))
+	assert.False(t, isGithubCopilotProvider(""))
+}
+
+func TestIsCopilotResponsesModel(t *testing.T) {
+	t.Parallel()
+
+	assert.True(t, isCopilotResponsesModel("gpt-5.3-codex"))
+	assert.True(t, isCopilotResponsesModel("gpt-5.2-codex"))
+	assert.False(t, isCopilotResponsesModel("gpt-4o"))
+	assert.False(t, isCopilotResponsesModel("claude-sonnet-4-5"))
+	assert.False(t, isCopilotResponsesModel(""))
+}
+
+func TestGithubCopilotApiType(t *testing.T) {
+	cfg := &latest.ModelConfig{
+		Provider: "github-copilot",
+		Model:    "gpt-5.3-codex",
+	}
+
+	enhancedCfg := applyProviderDefaults(cfg, nil)
+
+	apiType := resolveProviderType(enhancedCfg)
+
+	if apiType != "openai_responses" {
+		t.Errorf("Expected api_type to be 'openai_responses', got '%s'", 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)
+
+	if apiType2 != "openai_responses" {
+		t.Errorf("Expected api_type to be 'openai_responses', got '%s'", apiType2)
+	}
+}