Structured streaming doesn't work with claude (Stream Whale example)

[sgondala]

Initial Checks

• I confirm that I'm using the latest version of Pydantic AI
• I confirm that I searched for my issue in https://github.com/pydantic/pydantic-ai/issues before opening this issue

Description

Structured streaming doesn't doesn’t work with Claude.

I tried using stream whales example as-is. While using openai:gpt-4, we see the expected streaming behavior with the table populating progressively. However, when switching to anthropic:claude-3-7-sonnet-latest, the output appears all at once rather than streaming incrementally.

Example Code

import os
from typing import Annotated

import logfire
from dotenv import load_dotenv
from pydantic import Field, ValidationError
from pydantic_ai import Agent
from rich.console import Console
from rich.live import Live
from rich.table import Table
from typing_extensions import NotRequired, TypedDict

load_dotenv()

# 'if-token-present' means nothing will be sent (and the example will work) if you don't have logfire configured
logfire.configure(send_to_logfire="if-token-present")


class Whale(TypedDict):
    name: str
    length: Annotated[float, Field(description="Average length of an adult whale in meters.")]
    weight: NotRequired[
        Annotated[
            float,
            Field(description="Average weight of an adult whale in kilograms.", ge=50),
        ]
    ]
    ocean: NotRequired[str]
    description: NotRequired[Annotated[str, Field(description="Short Description")]]


agent = Agent("anthropic:claude-3-7-sonnet-latest", output_type=list[Whale], instrument=True)


async def main():
    console = Console()
    with Live("\n" * 36, console=console) as live:
        console.print("Requesting data...", style="cyan")
        async with agent.run_stream("Generate me details of 5 species of Whale.") as result:
            console.print("Response:", style="green")

            async for message, last in result.stream_structured(debounce_by=0.01):
                try:
                    whales = await result.validate_structured_output(message, allow_partial=not last)
                except ValidationError as exc:
                    if all(e["type"] == "missing" and e["loc"] == ("response",) for e in exc.errors()):
                        continue
                    else:
                        raise

                table = Table(
                    title="Species of Whale",
                    caption="Streaming Structured responses from GPT-4",
                    width=120,
                )
                table.add_column("ID", justify="right")
                table.add_column("Name")
                table.add_column("Avg. Length (m)", justify="right")
                table.add_column("Avg. Weight (kg)", justify="right")
                table.add_column("Ocean")
                table.add_column("Description", justify="right")

                for wid, whale in enumerate(whales, start=1):
                    table.add_row(
                        str(wid),
                        whale["name"],
                        f'{whale["length"]:0.0f}',
                        f"{w:0.0f}" if (w := whale.get("weight")) else "…",
                        whale.get("ocean") or "…",
                        whale.get("description") or "…",
                    )
                live.update(table)


if __name__ == "__main__":
    import asyncio

    asyncio.run(main())

Python, Pydantic AI & LLM client version

python = 3.10 
pydantic ai = 0.1.10
llm = anthropic:claude-3-7-sonnet-latest

[DouweM]

@sgondala Thanks for the report, I've implemented a fix in #1669.