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HomeDocsClaude Code CLI 25 Sep 2026
One change · claude-code

Scale to many tools with tool search changedagent-sdk/tool-search

Nearest release: v2.1.283, published 4 hours before upstream edited the page. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.

Upstream edited this page at 25 Sep 2026 22:47 UTC, give or take a minute or two: the time comes from Anthropic’s own sitemap rather than from a commit. This site recorded the change at 28 Sep 2026 23:37 UTC.

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3434 
3535The SDK also disables tool search when `ANTHROPIC_BASE_URL` points to a non-first-party host, since most proxies don't forward `tool_reference` blocks. You can override that default with the `ENABLE_TOOL_SEARCH` environment variable:
3636 
37| Value | Behavior |
38| :------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
39| (unset) | Tool search is on. Tool definitions are deferred and discovered on demand. Falls back to loading upfront on Google Cloud's Agent Platform models earlier than the Claude 4.5 generation, a non-first-party `ANTHROPIC_BASE_URL`, or a Microsoft Foundry deployment hosted on Azure. |
40| `true` | Tool search is always on, except on a Microsoft Foundry deployment hosted on Azure, where the server-side rejection still forces upfront loading, and on Google Cloud's Agent Platform models earlier than the Claude 4.5 generation, where the SDK keeps loading tool definitions upfront. The SDK sends the beta header through proxies, and requests fail on proxies that don't support `tool_reference` blocks. |
41| `auto` | Counts the tokens in the tool definitions that tool search can defer and compares the total against the model's context window. When the total reaches 10% of the window, tool search activates. Below that, the SDK loads every tool definition into context upfront. |
42| `auto:N` | Same as `auto` with a custom percentage. `auto:5` activates when those definitions reach 5% of the context window. Lower values activate sooner. |
43| `false` | Tool search is off. All tool definitions are loaded into context on every turn. |
37| Value | Behavior |
38| :- | :- |
39| (unset) | Tool search is on. Tool definitions are deferred and discovered on demand. Falls back to loading upfront on Google Cloud's Agent Platform models earlier than the Claude 4.5 generation, a non-first-party `ANTHROPIC_BASE_URL`, or a Microsoft Foundry deployment hosted on Azure. |
40| `true` | Tool search is always on, except on a Microsoft Foundry deployment hosted on Azure, where the server-side rejection still forces upfront loading, and on Google Cloud's Agent Platform models earlier than the Claude 4.5 generation, where the SDK keeps loading tool definitions upfront. The SDK sends the beta header through proxies, and requests fail on proxies that don't support `tool_reference` blocks. |
41| `auto` | Counts the tokens in the tool definitions that tool search can defer and compares the total against the model's context window. When the total reaches 10% of the window, tool search activates. Below that, the SDK loads every tool definition into context upfront. |
42| `auto:N` | Same as `auto` with a custom percentage. `auto:5` activates when those definitions reach 5% of the context window. Lower values activate sooner. |
43| `false` | Tool search is off. All tool definitions are loaded into context on every turn. |
4444 
4545Setting [`CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS`](/docs/en/env-vars) keeps tool search off. You can't override it by setting `ENABLE_TOOL_SEARCH` yourself. Your organization can keep tool search on through [managed settings](/docs/en/managed-settings), on Claude Code v2.1.227 or later. [Disable pre-release capabilities](/docs/en/llm-gateway-protocol#disable-pre-release-capabilities) covers where the override applies and what the variable strips.
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