Passing any value for `model_kwargs` in ChatBedrockConverse results in Circular reference error

[peterkarman1]

When trying to pass model_kwargs, using this parameter at all causes a circular reference error. Here is a minimal reproduction

model = ChatBedrockConverse(
            model="qwen.qwen3-coder-480b-a35b-v1:0",
            model_kwargs={"test": AppConfig.MAX_OUTPUT_TOKENS},
            region_name=region_name,
            stop=None,
            client=client,
        )

model.invoke("hello world")

/lib/python3.12/site-packages/langchain_core/load/dump.py", line 64, in dumps\n    return json.dumps(obj, default=default, **kwargs)\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File "/Users/peterkarman/.local/share/uv/python/cpython-3.12.8-macos-aarch64-none/lib/python3.12/json/__init__.py", line 238, in dumps\n    **kw).encode(obj)\n          ^^^^^^^^^^^\n  File "/Users/peterkarman/.local/share/uv/python/cpython-3.12.8-macos-aarch64-none/lib/python3.12/json/encoder.py", line 200, in encode\n    chunks = self.iterencode(o, _one_shot=True)\n             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File "/Users/peterkarman/.local/share/uv/python/cpython-3.12.8-macos-aarch64-none/lib/python3.12/json/encoder.py", line 258, in iterencode\n    return _iterencode(o, 0)\n           ^^^^^^^^^^^^^^^^^\nValueError: Circular reference detected\n'
```

[michaelnchin]

@peterkarman1 thanks! A fix to handle this error is pending in #715.

Do note that model_kwargs is not meant to be supported for ChatBedockConverse - please use additional_model_request_fields(also see: Bedrock docs) instead. This will work on the latest version of langchain-aws.

[peterkarman1]

@michaelnchin the additional_model_request_fields did indeed work for me.

Also just wanted to say, appreciate your work here. You've been jumping on everything quick. Thank you!