Methods `writeSource` and `writeMessageAnnotation` do not update data of `sources` and `messages[i].annotations` in `StreamTextOnFinishCallback`

[carlosleandr]

Description

I'm using the methods writeSource and writeMessageAnnotation in onChunk and expected that by the end of transmission, this data would be present in onFinish, but it's not. Is this intentional?

On frontend, useChat hook correctly receives these sources and annotations and adds them to the messages, as theoretically should happen at the end of transmission on backend.

Screenshot from browser console:

My code:

return createDataStreamResponse({
    execute: (dataStream) => {
        const result = streamText({
            model: openai('gpt-4'),
            system: process.env.DEFAULT_PROMPT,
            messages,
            tools: { getWeather },
            experimental_transform: smoothStream({ chunking: 'word' }),
            experimental_generateMessageId: generateUUID,
            onChunk: ({ chunk }) => {
                if (
                    urlPattern &&
                    chunk.type === 'text-delta' &&
                    chunk.textDelta.length >= 30
                ) {
                    const url = urlPattern.exec(chunk.textDelta)?.[0];
                    if (url) {
                        dataStream.writeSource({
                            id: url,
                            url,
                            title: urlTitles[url],
                            sourceType: 'url',
                        });
                        dataStream.writeMessageAnnotation({
                            id: url,
                            url,
                            title: urlTitles[url],
                            sourceType: 'url',
                        });
                    }
                }
            },
            onFinish: async ({ response: { messages }, sources }) => {
                // `sources` is empty
                // `messages[i].annotations` is undefined
                // `messages[i].parts[i].type==='source'` doesnt exist
            },
        });
        result.consumeStream();
        result.mergeIntoDataStream(dataStream, {
            sendReasoning: true,
            sendSources: true,
        });
    },
}

AI SDK Version

• ai: 4.3.4
• @ai-sdk/react: 1.2.8
• @ai-sdk/openai: 1.3.10