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HomeDocsClaude Code CLI 6 Nov 2026
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How Claude Code uses prompt caching changedprompt-caching

Nearest release: v2.1.319, published 2 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 6 Nov 2026 03:39 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 6 Nov 2026 04:07 UTC.

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9999[Fast mode](https://code.claude.com/docs/en/fast-mode.md) and standard speed keep separate caches, so after you turn fast mode on or off, the next request can't use what the other speed cached. The first time you turn fast mode on in a conversation, the next request reads the whole conversation so far uncached at [fast mode rates](https://code.claude.com/docs/en/fast-mode.md#understand-the-cost-tradeoff). To keep that cost small, turn it on at the start of a session.
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101101* If you turn it on while Claude is working, that turn finishes at standard speed, and you pay for any uncached read on your next turn's first request.
102* If your current model doesn't support fast mode, enabling fast mode also [switches you to Opus](https://code.claude.com/docs/en/fast-mode.md#toggle-fast-mode). That [model switch](#switching-models) starts a fresh cache on its own from the next request in the running turn.
102* If your current model doesn't support fast mode, running `/fast` also [switches you to Opus](https://code.claude.com/docs/en/fast-mode.md#toggle-fast-mode). That [model switch](#switching-models) starts a fresh cache on its own from the next request in the running turn.
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104104Each later toggle reads uncached whatever the speed you switch to doesn't have cached. Speed changes Claude Code makes on its own, such as the [fallback to standard speed](https://code.claude.com/docs/en/fast-mode.md#handle-rate-limits) after a rate limit and the return to fast mode later, count as toggles too.
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