# Repeated assistant messages in useChat

## Issue

When using `useChat` with `streamText` on the server, the assistant's messages appear duplicated in the UI - showing both the previous message and the new message, or showing the same message multiple times. This can occur when using tool calls or complex message flows.

```tsx
// Server-side code that may experience assistant message duplication on the client
export async function POST(req: Request) {
  const { messages } = await req.json();

  const result = streamText({
    model: 'openai/gpt-5-mini',
    messages: convertToModelMessages(messages),
    tools: {
      weather: {
        description: 'Get the weather for a location',
        parameters: z.object({
          location: z.string(),
        }),
        execute: async ({ location }) => {
          return { temperature: 72, condition: 'sunny' };
        },
      },
    },
  });

  return result.toUIMessageStreamResponse();
}
```

## Background

The duplication occurs because `toUIMessageStreamResponse` generates new message IDs for each new message.

## Solution

Pass the original messages array to `toUIMessageStreamResponse` using the `originalMessages` option. By passing `originalMessages`, the method can reuse existing message IDs instead of generating new ones, ensuring the client properly updates existing messages rather than creating duplicates.

```tsx
export async function POST(req: Request) {
  const { messages } = await req.json();

  const result = streamText({
    model: 'openai/gpt-5-mini',
    messages: convertToModelMessages(messages),
    tools: {
      weather: {
        description: 'Get the weather for a location',
        parameters: z.object({
          location: z.string(),
        }),
        execute: async ({ location }) => {
          return { temperature: 72, condition: 'sunny' };
        },
      },
    },
  });

  return result.toUIMessageStreamResponse({
    originalMessages: messages, // Pass the original messages here
    generateMessageId: generateId,
    onFinish: ({ messages }) => {
      saveChat({ id, messages });
    },
  });
}
```


## Navigation

- [Azure OpenAI Slow to Stream](/v5/docs/troubleshooting/azure-stream-slow)
- [Client-Side Function Calls Not Invoked](/v5/docs/troubleshooting/client-side-function-calls-not-invoked)
- [Server Actions in Client Components](/v5/docs/troubleshooting/server-actions-in-client-components)
- [useChat/useCompletion stream output contains 0:... instead of text](/v5/docs/troubleshooting/strange-stream-output)
- [Streamable UI Errors](/v5/docs/troubleshooting/streamable-ui-errors)
- [Tool Invocation Missing Result Error](/v5/docs/troubleshooting/tool-invocation-missing-result)
- [Streaming Not Working When Deployed](/v5/docs/troubleshooting/streaming-not-working-when-deployed)
- [Streaming Not Working When Proxied](/v5/docs/troubleshooting/streaming-not-working-when-proxied)
- [Getting Timeouts When Deploying on Vercel](/v5/docs/troubleshooting/timeout-on-vercel)
- [Unclosed Streams](/v5/docs/troubleshooting/unclosed-streams)
- [useChat Failed to Parse Stream](/v5/docs/troubleshooting/use-chat-failed-to-parse-stream)
- [Server Action Plain Objects Error](/v5/docs/troubleshooting/client-stream-error)
- [useChat No Response](/v5/docs/troubleshooting/use-chat-tools-no-response)
- [Custom headers, body, and credentials not working with useChat](/v5/docs/troubleshooting/use-chat-custom-request-options)
- [TypeScript performance issues with Zod and AI SDK 5](/v5/docs/troubleshooting/typescript-performance-zod)
- [useChat "An error occurred"](/v5/docs/troubleshooting/use-chat-an-error-occurred)
- [Repeated assistant messages in useChat](/v5/docs/troubleshooting/repeated-assistant-messages)
- [onFinish not called when stream is aborted](/v5/docs/troubleshooting/stream-abort-handling)
- [Tool calling with generateObject and streamObject](/v5/docs/troubleshooting/tool-calling-with-structured-outputs)
- [Abort breaks resumable streams](/v5/docs/troubleshooting/abort-breaks-resumable-streams)
- [streamText fails silently](/v5/docs/troubleshooting/stream-text-not-working)
- [Streaming Status Shows But No Text Appears](/v5/docs/troubleshooting/streaming-status-delay)
- [Stale body values with useChat](/v5/docs/troubleshooting/use-chat-stale-body-data)
- [Type Error with onToolCall](/v5/docs/troubleshooting/ontoolcall-type-narrowing)
- [Unsupported model version error](/v5/docs/troubleshooting/unsupported-model-version)
- [Object generation failed with OpenAI](/v5/docs/troubleshooting/no-object-generated-content-filter)
- [Model is not assignable to type "LanguageModelV1"](/v5/docs/troubleshooting/model-is-not-assignable-to-type)
- [TypeScript error "Cannot find namespace 'JSX'"](/v5/docs/troubleshooting/typescript-cannot-find-namespace-jsx)
- [React error "Maximum update depth exceeded"](/v5/docs/troubleshooting/react-maximum-update-depth-exceeded)
- [Jest: cannot find module '@ai-sdk/rsc'](/v5/docs/troubleshooting/jest-cannot-find-module-ai-rsc)


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