useChat not updating messages with streamed data from streamText

[ben-bwh]

Issue Summary

I'm building a React Single Page Application (SPA) that communicates with a serverless backend using Node.js, AWS API Gateway, and Lambda.

I'm trying to get useChat to read the data stream being returned by streamText but the messages variable never gets updated with an assistant message.

AI SDK version: 3.4.33

Client-side

const { messages, input, handleInputChange, handleSubmit, isLoading } =
    useChat({
      api: `${process.env.REACT_APP_BEDROCK_API_URL}/bedrock`,
      maxSteps: 5,
      headers: {
        Authorization: `Bearer ${token}`,
      },
      onResponse: (response) => {
        console.log('Chat response:', response);
      },
      onError: (error) => console.error('Chat error:', error),
    });

Server-side

export const handler = async (event: APIGatewayProxyEventV2) => {
  const conversation = JSON.parse(event.body || '{}').messages || [];

  const bedrock = createAmazonBedrock({
    bedrockOptions: {
      region: process.env.AWS_REGION,
    },
  });

  const model = bedrock('anthropic.claude-3-5-sonnet-20241022-v2:0');

  const result = await streamText({
    model,
    system: systemPrompt,
    messages: conversation,
    maxSteps: 3,
    tools: {
      supportArticles: tool({
        description:
          'Retrieves support articles about BestRev from the knowledge base to help answer the user query',
        parameters: z.object({
          query: z
            .string()
            .describe('The query to search for in the support articles'),
        }),
        execute: async ({ query }) => {
          const kbResult = await retrieveFromKnowledgeBase(query);
          return kbResult;
        },
      }),
    },
    onChunk: async ({ chunk }) => {
      console.log(JSON.stringify(chunk, null, 2));
    },
  });

  return result.toDataStreamResponse();
};

The onChunk method is logging the streamed response from the model correctly. Here is what gets logged in the onResponse method of useChat:

There are no errors being logged in the onError method.

I do have a tool for streamText to call when needed, but I'm not using prompts that trigger the tool while testing this.

[ben-bwh]

It appears the issue is likely due to API Gateway not supporting streaming. I tried to use a Lambda Function URL to get around this issue but didn't have any luck. If anyone has successfully implemented streaming with Lambda I would appreciate any insight or advice. Thanks!