fix(aws): Handle thinking with tools, use CountTokens API for Haiku 4.5 #698
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murilosimao
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Oct 29, 2025
….5 (langchain-ai#698) Couple of updates to ChatBedrock/ChatBedrockConverse for Haiku 4.5 support: - Allowlisted Haiku 4.5 to use CountTokens API for `get_num_tokens_from_messages()`. - Disabled forced tool use + thinking with `bind_tools()` and `with_structured_output()`, as Haiku (and Sonnet) 4.5 still do not support this. - Updated related unit/integration tests. - **NOTE:** The [`test_structured_output_tool_choice_not_supported`](https://github.com/langchain-ai/langchain-aws/blob/53298392adfbe2c02fcc14cf75383920b7935757/libs/aws/tests/integration_tests/chat_models/test_bedrock_converse.py#L436) Converse integration test has not been updated to include Haiku 4.5, which appears to behave very inconsistently with a structured output schema compared to previous Claude thinking models. Sonnet 4.5 and older models produce a tool call 100% of the time if the query is directly applicable to the schema. However, on Haiku 4.5, the chance of this happening was observed to be <5%.
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Couple of updates to ChatBedrock/ChatBedrockConverse for Haiku 4.5 support:
get_num_tokens_from_messages().bind_tools()andwith_structured_output(), as Haiku (and Sonnet) 4.5 still do not support this.test_structured_output_tool_choice_not_supportedConverse integration test has not been updated to include Haiku 4.5, which appears to behave very inconsistently with a structured output schema compared to previous Claude thinking models. Sonnet 4.5 and older models produce a tool call 100% of the time if the query is directly applicable to the schema. However, on Haiku 4.5, the chance of this happening was observed to be <5%.