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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 Developer Platform 22 Oct 2026
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mid-conversation-system-messages changedbuild-with-claude/mid-conversation-system-messages

Nearest release: v2.1.308, published 2 hours after this site recorded the change. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.

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From line 991 where the diff opens
First seen 14 Aug 2026 this site's first read of the page
Recorded edits24to this page, all time

The whole hunk

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992992The response's `content` includes a `tool_use` block for the new tool, for example:
993993 
994```json
994```text
995995{
996996 "type": "tool_use",
997997 "id": "toolu_01A09q90qw90lq917835lq9",
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10061006 
10071007A few rules follow from where the definition renders:
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1009* **Declare what you know up front.** A tool you know about at the first request belongs in `tools`, with `defer_loading: true` and a later `tool_addition` reference if it shouldn't be offered to the model yet. Define by value only what is unknown at the first request or changes later.
1009* **Declare what you know up front.** A tool you know about at the first request belongs in `tools`, with `defer_loading: true` and a later `tool_addition` reference if you don't want to offer it to the model yet. Define by value only what is unknown at the first request or changes later.
10101010* **Keep at least one non-deferred tool in `tools`.** A conversation whose `tools` array has no non-deferred tool is accepted, but the first tool it defines by value changes the start of the rendered prompt, which costs one full cache miss on that request. A [tool search tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/tool-search-tool) counts as non-deferred.
10111011* **Dated tool types keep their own beta headers.** If a server tool you define by value requires its own beta header, send that header on every later request in the conversation.
10121012* **`cache_control` goes on the block or in the definition, not both,** and counts toward the request's breakpoint limit. A deferred definition can't carry `cache_control`.
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