Messages changedapi/beta/messages
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Lines+429added
Lines−19removed
From line
133
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First seen
14 Aug 2026
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Recorded edits34to this page, all time
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from line 133, old and new numbered
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from line 133
133133
134134 - `"webhooks-2026-10-07"`
135135
136 - `"admin-user-sign-out-2026-10-08"`
137
136138 - `"message-threads-2026-08-12"`
137139
138140 - `"analytics-usage-cost-2026-08-24"`
from line 3130
31283130
31293131 See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.
31303132
3133 - `"claude-fable-5-2"`
3134
3135 Built for the most ambitious work in coding, enterprise workflows, and the sciences
3136
3137 - `"claude-mythos-5-2"`
3138
3139 Built for the most demanding cybersecurity and life sciences research, available through verification programs
3140
31313141 - `"claude-haiku-5-5"`
31323142
31333143 Fastest model for high-volume, real-time tasks
from line 3488
34783488 Accepted in `messages[].content` and not rendered into the prompt; not
34793489 validated against the request's `fallbacks` chain or top-level `model`.
34803490
3481 Echo the assistant turn back verbatim, including this block in its
3491 When you send the assistant turn back, keep this block in its
34823492 original position. The block marks the boundary between content produced
34833493 before and after a fallback hop, and the server relies on that boundary
34843494 to validate the turn: when thinking runs flank the boundary, omitting
from line 3495
34853495 the block merges them into one span the server cannot validate (the
34863496 request is rejected), and moving it into the middle of a single run is
34873497 likewise rejected; between non-thinking blocks the block's placement has
3488 no validation effect.
3498 no effect on thinking validation.
34893499
3500 Some blocks from before the turn's final `fallback` block must be left
3501 out when you send the turn back, and no `tool_result` is sent for a
3502 `tool_use` block you left out.
3503
3504 See the [refusals and fallback guide](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback?sdk_languages=http#continuing-the-conversation) to learn which blocks to keep.
3505
34903506 - `type: "fallback"`
34913507
34923508 - `from: BetaFallbackInfoParam`
from line 7018
70027018
70037019 Citations configuration for fetched documents. Citations are disabled by default.
70047020
7005 - `defer_loading: optional boolean`
7006
7007 If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.
7008
7009 - `max_content_tokens: optional number or null`
7010
7011 Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.
7012
7013 minimum: 1
7014
7015 - `max_uses: optional number or null`
7016
7017 Maximum number of times the tool can be used in the API request.
7018
7019 minimum: 1
7020
7021 - `response_inclusion: optional "full" or "excluded"`
7022
7023 How this tool's result blocks appear in the API resp
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