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Sweep 10 Nov 2026 · 02:18Z Build v2.1.322 539 read Stable v2.1.311 Latest v2.1.322 Next v2.1.322 Feeds RSS JSON llms.txt llms-full.txt Unofficial
HomeDocsClaude Developer Platform 9 Nov 2026
One change · api

message-threads changedbuild-with-claude/message-threads

Nearest release: v2.1.321, published under an hour before 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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First seen 2 Nov 2026 this site's first read of the page
Recorded edits4to this page, all time

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99 eligibility: not-eligible
1010 note: A thread's contents (the conversation, system prompt, and tools) are held in memory, encrypted under a server-managed key, never written to durable storage, and deleted no more than 1 hour after the thread's last use. Using this feature does not affect your use of other ZDR eligible features.
1111 supportedModels:
12 - claude-fable-5-2
13 - claude-mythos-5-2
1214 - claude-fable-5-1
1315 - claude-mythos-5-1
1416 - claude-fable-5
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600602 
601603To change a create-only or fixed field, start a new thread: send the full conversation in a create request with the new values.
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603On Claude Fable 5.1, Claude Mythos 5.1, Claude Opus 5.5, Claude Sonnet 5.5, and Claude Haiku 5.5, changing `system` or `tools` makes the `thinking` and `redacted_thinking` blocks already in the conversation invalid, and the create request can return a 400 error. To avoid it, leave every `thinking` and `redacted_thinking` block out of the conversation you send. The model then answers without that earlier reasoning. See [What counts as an edit](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#what-counts-as-an-edit), [When `prefix_mismatch_behavior` is unset](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#enforcement), and [What the API does with an invalid block](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#mismatch-behavior).
605On Claude Fable 5.2, Claude Mythos 5.2, Claude Fable 5.1, Claude Mythos 5.1, Claude Opus 5.5, Claude Sonnet 5.5, and Claude Haiku 5.5, changing `system` or `tools` makes the `thinking` and `redacted_thinking` blocks already in the conversation invalid, and the create request can return a 400 error. To avoid it, leave every `thinking` and `redacted_thinking` block out of the conversation you send. The model then answers without that earlier reasoning. See [What counts as an edit](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#what-counts-as-an-edit), [When `prefix_mismatch_behavior` is unset](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#enforcement), and [What the API does with an invalid block](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#mismatch-behavior).
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605607Send only the new messages on a continue request. The API doesn’t check them against the messages it already has. A message you send again can appear twice in the conversation, or the request can return an error. For example, a continue request that starts with the previous response returns an error.
606608 
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