diff --git a/packages/react-ai-sdk/src/ui/utils/useVercelAIThreadSync.tsx b/packages/react-ai-sdk/src/ui/utils/useVercelAIThreadSync.tsx
index 18b8ee1a9..096c791cf 100644
--- a/packages/react-ai-sdk/src/ui/utils/useVercelAIThreadSync.tsx
+++ b/packages/react-ai-sdk/src/ui/utils/useVercelAIThreadSync.tsx
@@ -72,6 +72,7 @@ const vercelToThreadMessage = (
                   type: "tool-call",
                   toolName: t.toolName,
                   toolCallId: t.toolCallId,
+                  argsText: JSON.stringify(t.args),
                   args: t.args,
                   result: "result" in t ? t.result : undefined,
                 }) satisfies ToolCallContentPart,
diff --git a/packages/react/src/runtimes/edge/streams/runResultStream.ts b/packages/react/src/runtimes/edge/streams/runResultStream.ts
index ccc2120c8..91121b0c5 100644
--- a/packages/react/src/runtimes/edge/streams/runResultStream.ts
+++ b/packages/react/src/runtimes/edge/streams/runResultStream.ts
@@ -31,7 +31,7 @@ export function runResultStream() {
             message,
             toolCallId,
             toolName,
-            parsePartialJson(currentToolCall.argsText),
+            currentToolCall.argsText,
           );
           controller.enqueue(message);
           break;
@@ -85,7 +85,7 @@ const appendOrUpdateToolCall = (
   message: ChatModelRunResult,
   toolCallId: string,
   toolName: string,
-  args: unknown,
+  argsText: string,
 ) => {
   let contentParts = message.content;
   let contentPart = message.content.at(-1);
@@ -97,13 +97,15 @@ const appendOrUpdateToolCall = (
       type: "tool-call",
       toolCallId,
       toolName,
-      args,
+      argsText,
+      args: parsePartialJson(argsText),
     };
   } else {
     contentParts = contentParts.slice(0, -1);
     contentPart = {
       ...contentPart,
-      args,
+      argsText,
+      args: parsePartialJson(argsText),
     };
   }
   return {
diff --git a/packages/react/src/types/AssistantTypes.ts b/packages/react/src/types/AssistantTypes.ts
index 011afef36..4db37879f 100644
--- a/packages/react/src/types/AssistantTypes.ts
+++ b/packages/react/src/types/AssistantTypes.ts
@@ -23,8 +23,10 @@ export type ToolCallContentPart<TArgs = unknown, TResult = unknown> = {
   type: "tool-call";
   toolCallId: string;
   toolName: string;
+  argsText: string;
   args: TArgs;
   result?: TResult;
+  isError?: boolean;
 };
 
 export type ThreadUserContentPart =