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fine-grained-tool-streaming changedagents-and-tools/tool-use/fine-grained-tool-streaming

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1919All 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), [Google Cloud](https://platform.claude.com/docs/en/build-with-claude/claude-on-vertex-ai), 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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21The `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. See [Tool reference](https://platform.claude.com/docs/en/agents-and-tools/tool-use/tool-reference) for the field definition.
21The `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.
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2323The 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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