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Sweep 22 Oct 2026 · 04:32Z Build v2.1.308 527 read Stable v2.1.308 Latest v2.1.308 Next v2.1.308 Feeds RSS JSON llms.txt llms-full.txt Unofficial
HomeDocsClaude Code CLI 21 Oct 2026
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Scale to many tools with tool search changedagent-sdk/tool-search

Nearest release: v2.1.306, published an hour after 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 21 Oct 2026 00:36 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 21 Oct 2026 00:37 UTC.

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3333Before Claude Code v2.1.221, the SDK disabled tool search for all models on Google Cloud's Agent Platform unless you set `ENABLE_TOOL_SEARCH`.
3434 
35The 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:
35> [!NOTE]
36>
37> Tool search is on by default behind an `ANTHROPIC_BASE_URL` gateway, with nothing to set. If the gateway rejects it, see [Tool search through an LLM gateway](/docs/en/mcp#tool-search-through-a-gateway). Before Claude Code v2.1.304, the SDK disabled tool search behind such a gateway unless `ENABLE_TOOL_SEARCH` was `true`, `auto`, or `auto:N`.
3638 
39You control whether and when tool definitions are deferred with the `ENABLE_TOOL_SEARCH` environment variable, which takes these values:
40 
3741| Value | Behavior |
3842| :- | :- |
39| (unset) | Tool search is on. Tool definitions are deferred and discovered on demand. Falls back to loading upfront on models earlier than Opus 4 and Sonnet 4, Google Cloud's Agent Platform models earlier than Opus 4.5, Sonnet 4.5, and Haiku 4.5, a non-first-party `ANTHROPIC_BASE_URL`, or a Microsoft Foundry deployment hosted on Azure. |
40| `true` | Tool search stays on with a non-first-party `ANTHROPIC_BASE_URL`. The other (unset) fallbacks still apply. The SDK sends the beta header through proxies, and requests fail on proxies that don't support `tool_reference` blocks. |
43| (unset) | Tool search is on, with tool definitions deferred and discovered on demand. Falls back to loading upfront on models earlier than Opus 4 and Sonnet 4, on the [earlier Agent Platform models](#configure-tool-search), and on Microsoft Foundry deployments hosted on Azure. |
44| `true` | Tool search is on, with the same fallbacks as (unset). |
4145| `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. |
4246| `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. |
4347| `false` | Tool search is off. All tool definitions are loaded into context on every turn. |
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