Create a Message changedapi/beta/messages/create
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Lines+188added
Lines−25removed
From line
16
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First seen
14 Aug 2026
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Recorded edits33to this page, all time
The whole hunk
from line 16, old and new numbered
/
from line 16
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 1398
13921398
13931399 See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.
13941400
1395 - `"claude-sonnet-5" or "claude-fable-5" or "claude-mythos-5" or 12 more`
1401 - `"claude-fable-5-1" or "claude-mythos-5-1" or "claude-sonnet-5" or 14 more`
13961402
13971403 The model that will complete your prompt.
13981404
13991405 See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.
14001406
1407 - `"claude-fable-5-1"`
1408
1409 Frontier intelligence for ambitious tasks across coding, scientific discovery, and enterprise workflows
1410
1411 - `"claude-mythos-5-1"`
1412
1413 Our most capable model for cybersecurity and biology research, available through trusted access programs
1414
14011415 - `"claude-sonnet-5"`
14021416
14031417 High-performance model for coding and agents
from line 1492
14781492
14791493 - `"system"`
14801494
1495 - `clear_at: optional "next_user_message" or "never" or null`
1496
1497 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.
1498
1499 - `"next_user_message"`
1500
1501 - `"never"`
1502
1503 - `output_config: optional BetaSystemMessageOutputConfig or null`
1504
1505 Per-message output configuration on a role:"system" input message.
1506
1507 Fields here apply per-turn; `format` remains top-level only. An
1508 empty `{}` is accepted on a message that carries content; a message
1509 with neither content nor output_config fields is rejected.
1510
1511 - `effort: optional "low" or "medium" or "high" or 2 more or null`
1512
1513 All possible effort levels.
1514
1515 - `"low"`
1516
1517 - `"medium"`
1518
1519 - `"high"`
1520
1521 - `"xhigh"`
1522
1523 - `"max"`
1524
14811525- `model: Model`
14821526
14831527 The model that will complete your prompt.
from line 1824
17801824
17811825 - `type: "enabled"`
17821826
1827 - `block_binding: optional BetaThinkingBlockBinding or null`
1828
1829 Controls for block binding: what happens when a thinking block this
1830 request sends back fails the conversation check. Every field is optional;
1831 an empty object means every default.
1832
1833 - `prefix_mismatch_behavior: optional BetaThinkingPrefixMismatchBehavior or null`
1834
1835 What happens when a thinking block in `messages` fails the conversation
1836 check: it was created in a different conversation, or the messages before
1837 it have changed since. `"error"` (the default) fails the request with a
1838 400 error. `"drop_block"` removes the failing blocks and the request
1839 proceeds; the model no longer sees the dropped reasoning.
1840
1841 - `"error"`
1842
1843 - `"drop_block"`
1844
17831845 - `display: optional "summarized" or "omitted" or "updates" or null`
17841846
17851847 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 1860
17981860
17991861 - `type: "adaptive"`
18001862
1863 - `block_binding: optional BetaThinkingBlockBinding or null`
1864
1865 Controls for block binding: what happens when a thinking block this
1866 request sends back fails the conversation check. Every field is optional;
1867 an empty object means every default.
1868
18011869 - `display: optional "summarized" or "omitted" or "updates" or null`
18021870
18031871 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 2367
22992367
23002368 - `type: "browser_toolset_20260801"`
23012369
2302 - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"`
2303
2304 - `"direct"`
2305
2306 - `"code_execution_20250825"`
2307
2308 - `"code_execution_20260120"`
2309
2310 - `"code_execution_20260521"`
2311
23122370 - `cache_control: optional BetaCacheControlEphemeral or null`
23132371
23142372 Create a cache control breakpoint at this content block.
from line 2993
29352993
29362994 - `type: "computer_toolset_20260801"`
29372995
2938 - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"`
2939
2940 - `"direct"`
2941
2942 - `"code_execution_20250825"`
2943
2944 - `"code_execution_20260120"`
2945
2946 - `"code_execution_20260521"`
2947
29482996 - `cache_control: optional BetaCacheControlEphemeral or null`
29492997
29502998 Create a cache control breakpoint at this content block.
from line 4874
48264874
48274875 See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.
48284876
4829 - `"claude-sonnet-5" or "claude-fable-5" or "claude-mythos-5" or 12 more`
4877 - `"claude-fable-5-1" or "claude-mythos-5-1" or "claude-sonnet-5" or 14 more`
48304878
48314879 The model that will complete your prompt.
48324880
48334881 See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.
48344882
4883 - `"claude-fable-5-1"`
4884
4885 Frontier intelligence for ambitious tasks across coding, scientific discovery, and enterprise workflows
4886
4887 - `"claude-mythos-5-1"`
4888
4889 Our most capable model for cybersecurity and biology research, available through trusted access programs
4890
48354891 - `"claude-sonnet-5"`
48364892
48374893 High-performance model for coding and agents
from line 5619
55635619
55645620 - `"fast"`
55655621
5622 - `input_transformations: optional array of BetaThinkingDroppedInputTransformation or null`
5623
5624 Changes the API made to the request's input before showing it to the model:
5625 one entry per change, in request order. Today the only entry type is
5626 `thinking_dropped` — a `thinking`, `redacted_thinking` or `connector_text`
5627 block from the request's `messages` that was removed from the prompt instead
5628 of being shown to the model because it failed a binding check. More entry
5629 types may be added over time; ignore types you do not recognize.
5630
5631 Requires `anthropic-beta: thinking-binding-controls-2026-08-01`. Present on
5632 every such response from a model that supports extended thinking, as `[]`
5633 when nothing was changed; without the beta, blocks are removed all the same
5634 but nothing is reported. Removed blocks contribute nothing to
5635 `usage.input_tokens`. When streaming, the array is final in `message_start`;
5636 the final `message_delta` event carries it only when a server-side model
5637 fallback happened mid-stream, in which case it holds the serving model's
5638 entries and replaces the one in `message_start`.
5639
5640 - `path: string`
5641
5642 Where the removed block was in your request, as `messages.{i}.content.{j}`:
5643 `i` indexes the `messages` array you sent and `j` that message's `content`
5644 array — the same form error messages use.
5645
5646 - `reason: "model_binding_mismatch" or "prefix_binding_mismatch" or "organization_binding_mismatch" or "end_user_binding_mismatch"`
5647
5648 Which binding check removed the block: `model_binding_mismatch` — it was
5649 created by a model whose reasoning the requested model may not read;
5650 `prefix_binding_mismatch` — the conversation before it differs from the
5651 conversation it was created in (the rest of that turn's consecutive thinking
5652 blocks are removed with it, each with this reason);
5653 `organization_binding_mismatch` — it was created under a different
5654 organization (an Anthropic organization, AWS account or Google Cloud project)
5655 and this organization is not one of its additional organizations;
5656 `end_user_binding_mismatch` — it was created for a different end user, or
5657 was removed by the consumer-organization binding. A block that would fail
5658 several checks reports one reason, in this order of precedence:
5659 `organization_binding_mismatch`, `end_user_binding_mismatch`,
5660 `model_binding_mismatch`, `prefix_binding_mismatch`.
5661
5662 - `"model_binding_mismatch"`
5663
5664 - `"prefix_binding_mismatch"`
5665
5666 - `"organization_binding_mismatch"`
5667
5668 - `"end_user_binding_mismatch"`
5669
5670 - `type: "thinking_dropped"`
5671
5672 Always `thinking_dropped` for this entry type.
5673
5674 default: thinking_dropped
5675
55665676- `BetaRawMessageStreamEvent = BetaRawMessageStartEvent or BetaRawMessageDeltaEvent or BetaRawMessageStopEvent or 3 more`
55675677
55685678 - `BetaRawMessageStartEvent object`
from line 5770
56605770
56615771 The number of server tool requests.
56625772
5773 - `input_transformations: optional array of BetaThinkingDroppedInputTransformation or null`
5774
5775 Changes the API made to the request's input before showing it to the model:
5776 one entry per change, in request order. Today the only entry type is
5777 `thinking_dropped` — a `thinking`, `redacted_thinking` or `connector_text`
5778 block from the request's `messages` that was removed from the prompt instead
5779 of being shown to the model because it failed a binding check. More entry
5780 types may be added over time; ignore types you do not recognize.
5781
5782 Requires `anthropic-beta: thinking-binding-controls-2026-08-01`. Present on
5783 every such response from a model that supports extended thinking, as `[]`
5784 when nothing was changed; without the beta, blocks are removed all the same
5785 but nothing is reported. Removed blocks contribute nothing to
5786 `usage.input_tokens`. When streaming, the array is final in `message_start`;
5787 the final `message_delta` event carries it only when a server-side model
5788 fallback happened mid-stream, in which case it holds the serving model's
5789 entries and replaces the one in `message_start`.
5790
5791 - `path: string`
5792
5793 Where the removed block was in your request, as `messages.{i}.content.{j}`:
5794 `i` indexes the `messages` array you sent and `j` that message's `content`
5795 array — the same form error messages use.
5796
5797 - `reason: "model_binding_mismatch" or "prefix_binding_mismatch" or "organization_binding_mismatch" or "end_user_binding_mismatch"`
5798
5799 Which binding check removed the block: `model_binding_mismatch` — it was
5800 created by a model whose reasoning the requested model may not read;
5801 `prefix_binding_mismatch` — the conversation before it differs from the
5802 conversation it was created in (the rest of that turn's consecutive thinking
5803 blocks are removed with it, each with this reason);
5804 `organization_binding_mismatch` — it was created under a different
5805 organization (an Anthropic organization, AWS account or Google Cloud project)
5806 and this organization is not one of its additional organizations;
5807 `end_user_binding_mismatch` — it was created for a different end user, or
5808 was removed by the consumer-organization binding. A block that would fail
5809 several checks reports one reason, in this order of precedence:
5810 `organization_binding_mismatch`, `end_user_binding_mismatch`,
5811 `model_binding_mismatch`, `prefix_binding_mismatch`.
5812
5813 - `type: "thinking_dropped"`
5814
5815 Always `thinking_dropped` for this entry type.
5816
5817 default: thinking_dropped
5818
56635819 - `BetaRawMessageStopEvent object`
56645820
56655821 - `type: "message_stop"`
from line 6108
59526108 "cache_creation_input_tokens": 0,
59536109 "cache_read_input_tokens": 0,
59546110 "input_tokens": 0,
5955 "model": "claude-sonnet-5",
6111 "model": "claude-fable-5-1",
59566112 "output_tokens": 0,
59576113 "type": "message"
59586114 }
from line 6123
59676123 },
59686124 "service_tier": "standard",
59696125 "speed": "standard"
5970 }
6126 },
6127 "input_transformations": [
6128 {
6129 "path": "path",
6130 "reason": "model_binding_mismatch",
6131 "type": "thinking_dropped"
6132 }
6133 ]
59716134}
59726135```
59736136
No line in this hunk matches that.