[Bug]: Anthropic integration doesn't accumulate streaming outputs with context manager `get_final_output`

[DanielPolatajko]

Describe the bug

When using Weave with the Anthropic integration, I would expect the outputs of async streaming API calls to be accumulated and passed to Weave when the stream is consumed. I found that when using the stream as a context manager and calling get_final_output, the call finishes but the outputs are not available on the trace. I've included a repro and a screenshot of the trace.

I'm using Weave 0.52.17, Python 3.12.11, Windows 11

Repro:

import weave
from anthropic import AsyncAnthropic
from dotenv import load_dotenv
import asyncio

load_dotenv()

weave.init(project_name="danielpolatajko-mars/test")

async def test_anthropic_streaming():
    client = AsyncAnthropic()
    async with client.messages.stream(
        model="claude-sonnet-4-0",
        max_tokens=1024,
        messages=[{"role": "user", "content": "Say hello and tell me a short joke!"}]
    ) as stream:
        response = await stream.get_final_message()
    print(response.content[0].text)
    return response

asyncio.run(test_anthropic_streaming())

Weave Project Link

https://wandb.ai/danielpolatajko-mars/test/weave/traces?view=traces_default&peekPath=%2Fdanielpolatajko-mars%2Ftest%2Fcalls%2F019aabcc-19fa-77f0-9caf-2c0ce50b0e09%3FhideTraceTree%3D0

Screenshots

Screenshot of the trace: