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Feature request: per-tool `eager_input_streaming` so `assistant.tool_call_delta` fires early for Anthropic models

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
62/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Quiet
Tech stack
java, javascript
Domain
api, backend

Research direction

Start by tracing the assistant.tool_call_delta flow and the per-tool definition API used by the proposed defineTool example, then inspect where Anthropic model options are sent. Done means a per-tool eager input streaming option is exposed and causes tool-call deltas to arrive incrementally for Anthropic models without changing existing behavior.

Written by the indexing model from the issue text.

Description

enhancement
What

The recently added assistant.tool_call_delta provides access to incremental tool call deltas. For recent OpenAI models (e.g. GPT 5.5), it works as expected to send deltas smoothly as they are generated. However, for Anthropic models (e.g. Claude Opus 4.8), the deltas arrive as a burst because Claude buffers them. Anthropic provided the eager_input_streaming flag for the expected behavior: https://platform.claude.com/docs/en/agents-and-tools/tool-use/fine-grained-tool-streaming#how-to-use-fine-grained-tool-streaming. But the SDK hasn't exposed this option yet.

Proposed Usage Example
defineTool("my_tool", {
    description,
    parameters,
    handler,
    eagerInputStreaming: true, // or a different name
});
Why

Responsiveness: for tools capable of handling partial arguments, this improves responsiveness when the whole response might take many seconds - sometimes minutes - to generate.

Dominant language
Java
Stars
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Forks
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Avg merge
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Merged PRs (30d)
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