Count tokens in a Message changedapi/beta/messages/count_tokens
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Recorded here
Lines+70added
Lines−22removed
From line
16
where the diff opens
First seen
14 Aug 2026
this site's first read of the page
Recorded edits29to this page, all time
The whole hunk
from line 16, old and new numbered
/
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1616
1717 - `string`
1818
19 - `"message-batches-2024-09-24" or "prompt-caching-2024-07-31" or "computer-use-2024-10-22" or 38 more`
19 - `"message-batches-2024-09-24" or "prompt-caching-2024-07-31" or "computer-use-2024-10-22" or 41 more`
2020
2121 - `"message-batches-2024-09-24"`
2222
from line 100
100100
101101 - `"ce-user-management-2026-07-13"`
102102
103 - `"mid-conversation-output-config-2026-07-01"`
104
105 - `"thinking-binding-controls-2026-08-01"`
106
107 - `"mid-conversation-system-clear-at-2026-08-21"`
108
103109- `"anthropic-user-profile-id": optional string`
104110
105111 The user profile ID to attribute this request to. Use when acting on behalf of a party other than your organization. Requires the `user-profiles` beta header.
from line 1386
13801386
13811387 See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.
13821388
1383 - `"claude-sonnet-5" or "claude-fable-5" or "claude-mythos-5" or 12 more`
1389 - `"claude-fable-5-1" or "claude-mythos-5-1" or "claude-sonnet-5" or 14 more`
13841390
13851391 The model that will complete your prompt.
13861392
13871393 See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.
13881394
1395 - `"claude-fable-5-1"`
1396
1397 Frontier intelligence for ambitious tasks across coding, scientific discovery, and enterprise workflows
1398
1399 - `"claude-mythos-5-1"`
1400
1401 Our most capable model for cybersecurity and biology research, available through trusted access programs
1402
13891403 - `"claude-sonnet-5"`
13901404
13911405 High-performance model for coding and agents
from line 1480
14661480
14671481 - `"system"`
14681482
1483 - `clear_at: optional "next_user_message" or "never" or null`
1484
1485 How long this system message's text stays in front of the model. `"never"` (the default) renders it on every request that includes it. `"next_user_message"` renders it only for the user turn it follows: once a later `role: "user"` message exists in `messages` the message stays in the array (send it unchanged) but is no longer shown to the model. Only permitted on `role: "system"` messages.
1486
1487 - `"next_user_message"`
1488
1489 - `"never"`
1490
1491 - `output_config: optional BetaSystemMessageOutputConfig or null`
1492
1493 Per-message output configuration on a role:"system" input message.
1494
1495 Fields here apply per-turn; `format` remains top-level only. An
1496 empty `{}` is accepted on a message that carries content; a message
1497 with neither content nor output_config fields is rejected.
1498
1499 - `effort: optional "low" or "medium" or "high" or 2 more or null`
1500
1501 All possible effort levels.
1502
1503 - `"low"`
1504
1505 - `"medium"`
1506
1507 - `"high"`
1508
1509 - `"xhigh"`
1510
1511 - `"max"`
1512
14691513- `model: Model`
14701514
14711515 The model that will complete your prompt.
from line 1748
17041748
17051749 - `type: "enabled"`
17061750
1751 - `block_binding: optional BetaThinkingBlockBinding or null`
1752
1753 Controls for block binding: what happens when a thinking block this
1754 request sends back fails the conversation check. Every field is optional;
1755 an empty object means every default.
1756
1757 - `prefix_mismatch_behavior: optional BetaThinkingPrefixMismatchBehavior or null`
1758
1759 What happens when a thinking block in `messages` fails the conversation
1760 check: it was created in a different conversation, or the messages before
1761 it have changed since. `"error"` (the default) fails the request with a
1762 400 error. `"drop_block"` removes the failing blocks and the request
1763 proceeds; the model no longer sees the dropped reasoning.
1764
1765 - `"error"`
1766
1767 - `"drop_block"`
1768
17071769 - `display: optional "summarized" or "omitted" or "updates" or null`
17081770
17091771 Controls how thinking content appears in the response. When set to `summarized`, thinking is returned normally. When set to `omitted`, thinking content is redacted but a signature is returned for multi-turn continuity. Defaults to `summarized`.
from line 1784
17221784
17231785 - `type: "adaptive"`
17241786
1787 - `block_binding: optional BetaThinkingBlockBinding or null`
1788
1789 Controls for block binding: what happens when a thinking block this
1790 request sends back fails the conversation check. Every field is optional;
1791 an empty object means every default.
1792
17251793 - `display: optional "summarized" or "omitted" or "updates" or null`
17261794
17271795 Controls how thinking content appears in the response. When set to `summarized`, thinking is returned normally. When set to `omitted`, thinking content is redacted but a signature is returned for multi-turn continuity. Defaults to `summarized`.
from line 2181
21132181
21142182 - `type: "browser_toolset_20260801"`
21152183
2116 - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"`
2117
2118 - `"direct"`
2119
2120 - `"code_execution_20250825"`
2121
2122 - `"code_execution_20260120"`
2123
2124 - `"code_execution_20260521"`
2125
21262184 - `cache_control: optional BetaCacheControlEphemeral or null`
21272185
21282186 Create a cache control breakpoint at this content block.
from line 2806
27482806 via `configs.zoom.enabled`.
27492807
27502808 - `type: "computer_toolset_20260801"`
2751
2752 - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"`
2753
2754 - `"direct"`
2755
2756 - `"code_execution_20250825"`
2757
2758 - `"code_execution_20260120"`
2759
2760 - `"code_execution_20260521"`
27612809
27622810 - `cache_control: optional BetaCacheControlEphemeral or null`
27632811
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