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Sweep 09 Oct 2026 · 17:27Z Build v2.1.296 517 read Stable v2.1.287 Latest v2.1.296 Next v2.1.296 Feeds RSS JSON llms.txt llms-full.txt Unofficial
HomeDocsClaude Developer Platform 8 Oct 2026
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reference changedmanaged-agents/reference

Nearest release: v2.1.294, published an hour 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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First seen 14 Aug 2026 this site's first read of the page
Recorded edits14to this page, all time

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7676 </Tab>
7777 
7878 <Tab title="System events">
79 | Type | Description |
80 | ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
81 | `system.message` | Append privileged system-level context that applies to the accompanying turn and all subsequent turns. Supported on Claude Fable 5.1, Claude Mythos 5.1, Claude Fable 5, Claude Mythos 5, Claude Opus 5.5, Claude Opus 5, Claude Opus 4.8, Claude Sonnet 5.5, and Claude Haiku 5.5. On an unsupported primary model the event is rejected with `model_does_not_support_mid_conversation_system`. |
79 | Type | Description |
80 | ---------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
81 | `system.message` | Append privileged system-level context that applies to the accompanying turn and all subsequent turns. For the models that accept it, see [Supported models](https://platform.claude.com/docs/en/managed-agents/events-and-streaming#supported-models). On an unsupported primary model the event is rejected with `model_does_not_support_mid_conversation_system`. |
8282 </Tab>
8383 
8484 <Tab title="Event deltas">
85 Event deltas are stream-only preview events. They are emitted on stream connections (session-level or per-thread) that opt in with the `event_deltas[]` parameter, and they are never persisted to the session's event history. See [Event deltas](https://platform.claude.com/docs/en/managed-agents/events-and-streaming#event-deltas) for opting in, accumulating, and reconciling them.
85 Event deltas are stream-only preview events. They are emitted on stream connections (session-level or per-thread) that opt in with the `event_deltas[]` parameter, and they are never persisted to the session's event history. See [Preview responses with event deltas](https://platform.claude.com/docs/en/managed-agents/event-deltas) for opting in, accumulating, and reconciling them.
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8787 | Type | Description |
8888 | ------------- | ------------------------------------------------------------------------------------------------------------------------ |
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