diff --git a/packages/core/src/transformer/anthropic.transformer.ts b/packages/core/src/transformer/anthropic.transformer.ts
index 3231c8029..cde24bfb1 100644
--- a/packages/core/src/transformer/anthropic.transformer.ts
+++ b/packages/core/src/transformer/anthropic.transformer.ts
@@ -168,6 +168,7 @@ export class AnthropicTransformer implements Transformer {
                 content: thinkingPart.thinking,
                 signature: thinkingPart.signature,
               };
+              assistantMessage.reasoning_content = thinkingPart.thinking;
             }
 
             messages.push(assistantMessage);
diff --git a/packages/core/src/transformer/reasoning.transformer.ts b/packages/core/src/transformer/reasoning.transformer.ts
index 758d1a171..ea4f3e733 100644
--- a/packages/core/src/transformer/reasoning.transformer.ts
+++ b/packages/core/src/transformer/reasoning.transformer.ts
@@ -12,6 +12,16 @@ export class ReasoningTransformer implements Transformer {
   async transformRequestIn(
     request: UnifiedChatRequest
   ): Promise<UnifiedChatRequest> {
+    request.messages.forEach((message) => {
+      if (
+        message.role === "assistant" &&
+        message.thinking?.content &&
+        !message.reasoning_content
+      ) {
+        message.reasoning_content = message.thinking.content;
+      }
+    });
+
     if (!this.enable) {
       request.thinking = {
         type: "disabled",
diff --git a/packages/core/src/types/llm.ts b/packages/core/src/types/llm.ts
index 9febba648..e7ed128ed 100644
--- a/packages/core/src/types/llm.ts
+++ b/packages/core/src/types/llm.ts
@@ -48,6 +48,7 @@ export type MessageContent = TextContent | ImageContent;
 export interface UnifiedMessage {
   role: "user" | "assistant" | "system" | "tool";
   content: string | null | MessageContent[];
+  reasoning_content?: string;
   tool_calls?: Array<{
     id: string;
     type: "function";