fine-grained-tool-streaming changedagents-and-tools/tool-use/fine-grained-tool-streaming
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4545All models support fine-grained tool streaming on the Claude API, [Amazon Bedrock](https://platform.claude.com/docs/en/build-with-claude/claude-in-amazon-bedrock), [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws), [Claude Models on Google Cloud (Google managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/google-managed), and [Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry). To use it, set `eager_input_streaming` to `true` on any user-defined tool where you want fine-grained streaming enabled, and enable streaming on your request.
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47The `eager_input_streaming` field is optional. Setting it to `true` turns on fine-grained streaming for that tool, and omitting it gives you standard buffered streaming, in which the API buffers and validates each parameter value before streaming it back. The exception is a request that still sends the legacy `fine-grained-tool-streaming-2025-05-14` beta header, which turns fine-grained streaming on for tools that leave the field unset. The per-tool field replaces that header, and an explicit `false` keeps buffered streaming for a tool even when a request still sends it. The legacy header cannot be combined with a [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) or [browser use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) toolset entry: the API rejects a request that sends both, so remove the header and set `eager_input_streaming` on the user-defined tools that need it. See [Tool reference](https://platform.claude.com/docs/en/agents-and-tools/tool-use/tool-reference) for the field definition.
47The `eager_input_streaming` field is optional. Setting it to `true` turns on fine-grained streaming for that tool, and omitting it gives you standard buffered streaming, in which the API buffers and validates each parameter value before streaming it back. The exception is a request that sends the `fine-grained-tool-streaming-2025-05-14` beta header, which turns fine-grained streaming on for tools that leave the field unset. The per-tool field replaces that header, and an explicit `false` keeps buffered streaming for a tool even when a request sends it. The header cannot be combined with a [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) or [browser use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) toolset entry: the API rejects a request that sends both, so remove the header and set `eager_input_streaming` on the user-defined tools that need it. See [Tool reference](https://platform.claude.com/docs/en/agents-and-tools/tool-use/tool-reference) for the field definition.
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4949The following example turns on fine-grained streaming for a `make_file` tool and asks Claude for a long poem, so the tool input is large enough to watch it stream in:
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5353 curl https://api.anthropic.com/v1/messages \
5454 -H "content-type: application/json" \
5555 -H "x-api-key: $ANTHROPIC_API_KEY" \
56 -H "anthropic-version: 2023-06-01" \
56 -H "anthropic-version: 2026-10-21" \
5757 -d '{
5858 "model": "claude-opus-5-5",
5959 "max_tokens": 65536,
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