diff --git a/pkg/providers/openai_compat/provider.go b/pkg/providers/openai_compat/provider.go
index 2958937c1..e14aa22f1 100644
--- a/pkg/providers/openai_compat/provider.go
+++ b/pkg/providers/openai_compat/provider.go
@@ -258,7 +258,12 @@ func (p *Provider) ChatStream(
 	requestBody := p.buildRequestBody(messages, tools, model, options)
 	requestBody["stream"] = true
 	if supportsStreamingUsage(p.apiBase) {
-		requestBody["stream_options"] = map[string]any{"include_usage": true}
+		streamOptions := map[string]any{}
+		if existing, ok := requestBody["stream_options"].(map[string]any); ok {
+			streamOptions = maps.Clone(existing)
+		}
+		streamOptions["include_usage"] = true
+		requestBody["stream_options"] = streamOptions
 	}
 
 	jsonData, err := json.Marshal(requestBody)
@@ -474,12 +479,7 @@ func (p *Provider) SupportsNativeSearch() bool {
 }
 
 func isNativeSearchHost(apiBase string) bool {
-	u, err := url.Parse(apiBase)
-	if err != nil {
-		return false
-	}
-	host := u.Hostname()
-	return host == "api.openai.com" || strings.HasSuffix(host, ".openai.azure.com")
+	return isOpenAINativeBaseURL(apiBase)
 }
 
 // isOpenAINativeBaseURL reports whether the given API base is the OpenAI or
diff --git a/pkg/providers/openai_compat/provider_test.go b/pkg/providers/openai_compat/provider_test.go
index d4597751f..280d67d51 100644
--- a/pkg/providers/openai_compat/provider_test.go
+++ b/pkg/providers/openai_compat/provider_test.go
@@ -991,7 +991,7 @@ func chatWithCacheKey(t *testing.T, apiBase string) map[string]any {
 	return requestBody
 }
 
-func chatStreamWithRequestBody(t *testing.T, apiBase string) map[string]any {
+func chatStreamWithRequestBody(t *testing.T, apiBase string, opts ...Option) map[string]any {
 	t.Helper()
 	var requestBody map[string]any
 
@@ -1016,7 +1016,7 @@ func chatStreamWithRequestBody(t *testing.T, apiBase string) map[string]any {
 	}))
 	defer server.Close()
 
-	p := NewProvider("key", server.URL, "")
+	p := NewProvider("key", server.URL, "", opts...)
 	p.apiBase = apiBase
 	p.httpClient = &http.Client{
 		Transport: roundTripperFunc(func(r *http.Request) (*http.Response, error) {
@@ -1057,6 +1057,26 @@ func TestProviderChatStream_IncludesUsageForOpenAI(t *testing.T) {
 	}
 }
 
+func TestProviderChatStream_PreservesExistingStreamOptions(t *testing.T) {
+	body := chatStreamWithRequestBody(
+		t,
+		"https://api.openai.com/v1",
+		WithExtraBody(map[string]any{
+			"stream_options": map[string]any{"custom_flag": true},
+		}),
+	)
+	streamOptions, ok := body["stream_options"].(map[string]any)
+	if !ok {
+		t.Fatalf("stream_options = %T, want map[string]any", body["stream_options"])
+	}
+	if got := streamOptions["custom_flag"]; got != true {
+		t.Fatalf("stream_options.custom_flag = %v, want true", got)
+	}
+	if got := streamOptions["include_usage"]; got != true {
+		t.Fatalf("stream_options.include_usage = %v, want true", got)
+	}
+}
+
 func TestProviderChatStream_OmitsUsageForNonOpenAI(t *testing.T) {
 	tests := []struct {
 		name    string