Count tokens in a Message changedapi/beta/messages/count_tokens
Nearest release: v2.1.322, published 2 hours 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.
Recorded here
Lines+18added
Lines−2removed
From line
131
where the diff opens
First seen
14 Aug 2026
this site's first read of the page
Recorded edits30to this page, all time
The whole hunk
from line 131, old and new numbered
/
from line 131
131131
132132 - `"webhooks-2026-10-07"`
133133
134 - `"admin-user-sign-out-2026-10-08"`
135
134136 - `"message-threads-2026-08-12"`
135137
136138 - `"analytics-usage-cost-2026-08-24"`
from line 3116
31143116
31153117 See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.
31163118
3119 - `"claude-fable-5-2"`
3120
3121 Built for the most ambitious work in coding, enterprise workflows, and the sciences
3122
3123 - `"claude-mythos-5-2"`
3124
3125 Built for the most demanding cybersecurity and life sciences research, available through verification programs
3126
31173127 - `"claude-haiku-5-5"`
31183128
31193129 Fastest model for high-volume, real-time tasks
from line 3474
34643474 Accepted in `messages[].content` and not rendered into the prompt; not
34653475 validated against the request's `fallbacks` chain or top-level `model`.
34663476
3467 Echo the assistant turn back verbatim, including this block in its
3477 When you send the assistant turn back, keep this block in its
34683478 original position. The block marks the boundary between content produced
34693479 before and after a fallback hop, and the server relies on that boundary
34703480 to validate the turn: when thinking runs flank the boundary, omitting
from line 3481
34713481 the block merges them into one span the server cannot validate (the
34723482 request is rejected), and moving it into the middle of a single run is
34733483 likewise rejected; between non-thinking blocks the block's placement has
3474 no validation effect.
3484 no effect on thinking validation.
3485
3486 Some blocks from before the turn's final `fallback` block must be left
3487 out when you send the turn back, and no `tool_result` is sent for a
3488 `tool_use` block you left out.
3489
3490 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.
34753491
34763492 - `type: "fallback"`
34773493
No line in this hunk matches that.