feature[anthropic]: dynamically set max_tokens

[ccurme]

Privileged issue

• I am a LangChain maintainer, or was asked directly by a LangChain maintainer to create an issue here.

Issue Content

Anthropic's messages API requires an integer max_tokens parameter, which is currently set at 1024 (also the example value in their reference doc for that parameter).

This is a bad fit for Anthropic's more recent models, which may generate reasoning, server-side tool invocations, and other varieties of content and have commensurately higher token limits (64,000 for Claude 3.7 and 4). ctrl+F for "max output" here to see limits for each model.

It would be nice to set this attribute to Optional[int] and, if None, set the value according to the model's documented maximum.

This is technically a breaking change.

[shivnathtathe]

@ccurme I suggest making max_tokens: Optional[int] but defaulting to 1024 if not provided. This keeps the current behavior unchanged and lets users set a higher limit manually when needed.

Example:

if max_tokens is None:
    max_tokens = 1024

This avoids any breaking change while adding flexibility.

[keenborder786]

@ccurme this issue has been resolved in the above PR. Can you please check?