diff --git a/pkg/providers/openai_compat/provider.go b/pkg/providers/openai_compat/provider.go
index 3a18b8b16..ff9109e96 100644
--- a/pkg/providers/openai_compat/provider.go
+++ b/pkg/providers/openai_compat/provider.go
@@ -116,7 +116,7 @@ func (p *Provider) Chat(
 
 	requestBody := map[string]any{
 		"model":    model,
-		"messages": stripSystemParts(messages),
+		"messages": serializeMessages(messages),
 	}
 
 	if len(tools) > 0 {
@@ -296,19 +296,55 @@ type openaiMessage struct {
 	ToolCallID       string     `json:"tool_call_id,omitempty"`
 }
 
-// stripSystemParts converts []Message to []openaiMessage, dropping the
-// SystemParts field so it doesn't leak into the JSON payload sent to
-// OpenAI-compatible APIs (some strict endpoints reject unknown fields).
-func stripSystemParts(messages []Message) []openaiMessage {
-	out := make([]openaiMessage, len(messages))
-	for i, m := range messages {
-		out[i] = openaiMessage{
-			Role:             m.Role,
-			Content:          m.Content,
-			ReasoningContent: m.ReasoningContent,
-			ToolCalls:        m.ToolCalls,
-			ToolCallID:       m.ToolCallID,
+// serializeMessages converts internal Message structs to the OpenAI wire format.
+// - Strips SystemParts (unknown to third-party endpoints)
+// - Converts messages with Media to multipart content format (text + image_url parts)
+// - Preserves ToolCallID, ToolCalls, and ReasoningContent for all messages
+func serializeMessages(messages []Message) []any {
+	out := make([]any, 0, len(messages))
+	for _, m := range messages {
+		if len(m.Media) == 0 {
+			out = append(out, openaiMessage{
+				Role:             m.Role,
+				Content:          m.Content,
+				ReasoningContent: m.ReasoningContent,
+				ToolCalls:        m.ToolCalls,
+				ToolCallID:       m.ToolCallID,
+			})
+			continue
 		}
+
+		// Multipart content format for messages with media
+		parts := make([]map[string]any, 0, 1+len(m.Media))
+		if m.Content != "" {
+			parts = append(parts, map[string]any{
+				"type": "text",
+				"text": m.Content,
+			})
+		}
+		for _, mediaURL := range m.Media {
+			parts = append(parts, map[string]any{
+				"type": "image_url",
+				"image_url": map[string]any{
+					"url": mediaURL,
+				},
+			})
+		}
+
+		msg := map[string]any{
+			"role":    m.Role,
+			"content": parts,
+		}
+		if m.ToolCallID != "" {
+			msg["tool_call_id"] = m.ToolCallID
+		}
+		if len(m.ToolCalls) > 0 {
+			msg["tool_calls"] = m.ToolCalls
+		}
+		if m.ReasoningContent != "" {
+			msg["reasoning_content"] = m.ReasoningContent
+		}
+		out = append(out, msg)
 	}
 	return out
 }
diff --git a/pkg/providers/openai_compat/provider_test.go b/pkg/providers/openai_compat/provider_test.go
index 53b9e75ee..9d3b91a1a 100644
--- a/pkg/providers/openai_compat/provider_test.go
+++ b/pkg/providers/openai_compat/provider_test.go
@@ -5,8 +5,11 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"net/url"
+	"strings"
 	"testing"
 	"time"
+
+	"github.com/sipeed/picoclaw/pkg/providers/protocoltypes"
 )
 
 func TestProviderChat_UsesMaxCompletionTokensForGLM(t *testing.T) {
@@ -416,3 +419,98 @@ func TestProvider_FunctionalOptionRequestTimeoutNonPositive(t *testing.T) {
 		t.Fatalf("http timeout = %v, want %v", p.httpClient.Timeout, defaultRequestTimeout)
 	}
 }
+
+func TestSerializeMessages_PlainText(t *testing.T) {
+	messages := []protocoltypes.Message{
+		{Role: "user", Content: "hello"},
+		{Role: "assistant", Content: "hi", ReasoningContent: "thinking..."},
+	}
+	result := serializeMessages(messages)
+
+	data, err := json.Marshal(result)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var msgs []map[string]any
+	json.Unmarshal(data, &msgs)
+
+	if msgs[0]["content"] != "hello" {
+		t.Fatalf("expected plain string content, got %v", msgs[0]["content"])
+	}
+	if msgs[1]["reasoning_content"] != "thinking..." {
+		t.Fatalf("reasoning_content not preserved, got %v", msgs[1]["reasoning_content"])
+	}
+}
+
+func TestSerializeMessages_WithMedia(t *testing.T) {
+	messages := []protocoltypes.Message{
+		{Role: "user", Content: "describe this", Media: []string{"data:image/png;base64,abc123"}},
+	}
+	result := serializeMessages(messages)
+
+	data, _ := json.Marshal(result)
+	var msgs []map[string]any
+	json.Unmarshal(data, &msgs)
+
+	content, ok := msgs[0]["content"].([]any)
+	if !ok {
+		t.Fatalf("expected array content for media message, got %T", msgs[0]["content"])
+	}
+	if len(content) != 2 {
+		t.Fatalf("expected 2 content parts, got %d", len(content))
+	}
+
+	textPart := content[0].(map[string]any)
+	if textPart["type"] != "text" || textPart["text"] != "describe this" {
+		t.Fatalf("text part mismatch: %v", textPart)
+	}
+
+	imgPart := content[1].(map[string]any)
+	if imgPart["type"] != "image_url" {
+		t.Fatalf("expected image_url type, got %v", imgPart["type"])
+	}
+	imgURL := imgPart["image_url"].(map[string]any)
+	if imgURL["url"] != "data:image/png;base64,abc123" {
+		t.Fatalf("image url mismatch: %v", imgURL["url"])
+	}
+}
+
+func TestSerializeMessages_MediaWithToolCallID(t *testing.T) {
+	messages := []protocoltypes.Message{
+		{Role: "tool", Content: "image result", Media: []string{"data:image/png;base64,xyz"}, ToolCallID: "call_1"},
+	}
+	result := serializeMessages(messages)
+
+	data, _ := json.Marshal(result)
+	var msgs []map[string]any
+	json.Unmarshal(data, &msgs)
+
+	if msgs[0]["tool_call_id"] != "call_1" {
+		t.Fatalf("tool_call_id not preserved with media, got %v", msgs[0]["tool_call_id"])
+	}
+	// Content should be multipart array
+	if _, ok := msgs[0]["content"].([]any); !ok {
+		t.Fatalf("expected array content, got %T", msgs[0]["content"])
+	}
+}
+
+func TestSerializeMessages_StripsSystemParts(t *testing.T) {
+	messages := []protocoltypes.Message{
+		{
+			Role:    "system",
+			Content: "you are helpful",
+			SystemParts: []protocoltypes.ContentBlock{
+				{Type: "text", Text: "you are helpful"},
+			},
+		},
+	}
+	result := serializeMessages(messages)
+
+	data, _ := json.Marshal(result)
+	raw := string(data)
+	if strings.Contains(raw, "system_parts") {
+		t.Fatal("system_parts should not appear in serialized output")
+	}
+}
+