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HomeDocsClaude Code CLI 21 Oct 2026
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How Claude Code uses prompt caching changedprompt-caching

Nearest release: v2.1.306, published 3 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 21 Oct 2026 06:28 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 06:37 UTC.

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105105Tool definitions sit in the system prompt layer, so the cache invalidates when the set of tool definitions in the request changes between turns. Toggling the [advisor tool](/docs/en/advisor) is an exception: its definition sits after the cache breakpoint, so enabling or disabling `/advisor` keeps the cached prefix intact. Whether an [MCP server](/docs/en/mcp) change does this depends on whether [tool search](/docs/en/mcp#scale-with-mcp-tool-search) defers the session's MCP tools, the default on supported models:
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107107* **Tools deferred**: Claude Code keeps the tool list from the conversation's first request for the whole conversation, so a server connecting or disconnecting mid-session doesn't disturb anything already cached. A server that finishes connecting after the first request supplies its tools as deferred definitions that Claude loads on demand.
108* **Tools loaded upfront**: adding a definition invalidates the cache, and so does removing one on purpose. This applies when tool search is [below its `auto` threshold, disabled, or unavailable](/docs/en/mcp#configure-tool-search), such as on:
108* **Tools loaded upfront**: adding a definition invalidates the cache, and so does removing one on purpose. This applies when tool search is [off or unavailable](/docs/en/mcp#configure-tool-search), such as on:
109109 * Google Cloud's Agent Platform models earlier than Opus 4.5, Sonnet 4.5, and Haiku 4.5
110110 * A Microsoft Foundry [deployment hosted on Azure](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry#hosting-options) once Claude Code detects that the deployment rejects tool search
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