--- title: "Changes to Create a Message" method: POST path: "/v1/messages" --- # Changes to Create a Message `POST /v1/messages` > Every recorded change to this operation, newest first. ## Timeline Changed in 45 of 250 revisions. - **2026-10-30** `db779c2e7b5f`: 1 breaking, 6 info - **2026-10-21** `94c83daca660`: 1 breaking, 5 warning, 2 info - **2026-10-17** `bfa6803cbf21`: 1 breaking, 5 info - **2026-10-14** `569b1fb6ea2e`: 2 info - **2026-10-09** `ee978b5e1294`: 1 breaking, 3 info - **2026-10-08** `5b6f4c063051`: 5 breaking, 25 info - **2026-10-07** `2705c258c5dc`: 2 info - **2026-09-30** `d721a6487a16`: 1 breaking, 3 info - **2026-09-28** `3cd29369f196`: 1 breaking, 3 info - **2026-09-28** `36794f5ab00f`: 2 info - **2026-09-28** `231c3ffb9f5c`: 2 info - **2026-09-28** `86153a702615`: 1 breaking, 6 info - **2026-09-22** `257523f5aeb5`: 2 info - **2026-09-15** `3449c49f2da8`: 4 info - **2026-09-10** `e46a40fc336b`: 1 warning, 1 info - **2026-09-04** `e2857e722bed`: 1 breaking - **2026-09-04** `4789294140a2`: 17 info - **2026-09-01** `d1d189d791d1`: 2 warning, 2 info - **2026-08-19** `67ee007cda1c`: 29 info - **2026-08-19** `e9d8152420c3`: 1 breaking, 1 info - **2026-08-13** `6e9020ec2b41`: 27 info - **2026-08-07** `538e9bd0db77`: 1 breaking, 1 info - **2026-07-24** `a97790bd7f18`: 1 breaking, 3 info - **2026-07-23** `d7893c708340`: 1 warning - **2026-07-21** `97200025c28e`: 1 warning - **2026-07-01** `9c991bee394d`: 1 info - **2026-06-30** `7caa9a75ddbc`: 2 info - **2026-06-29** `4465f98f96c1`: 1 info - **2026-06-24** `82c21eb736c8`: 1 warning, 1 info - **2026-06-18** `063bcb9d6cf9`: 1 breaking, 18 info - **2026-06-09** `996eb28b2ab6`: 1 warning - **2026-06-09** `00259327305f`: 1 breaking, 1 warning, 3 info - **2026-06-06** `546c704d347b`: 1 breaking, 4 info - **2026-05-28** `f9d488f9290d`: 1 warning, 7 info - **2026-05-06** `a4186730f56c`: 1 breaking - **2026-04-30** `6edc6519fd32`: 1 breaking, 1 info - **2026-04-16** `e0696f59ae07`: 1 breaking, 4 info - **2026-04-08** `69486316563e`: 1 breaking, 6 info - **2026-04-01** `efe26b096126`: 1 info - **2026-03-18** `dd2dcd00a757`: 1 info - **2026-03-16** `7fce94a3c9f7`: 1 breaking, 6 info - **2026-02-19** `29a6b7ba5194`: 1 info - **2026-02-18** `5387c517ad6a`: 15 info - **2026-02-17** `6924f88807cb`: 1 breaking, 1 warning - **2026-02-17** `53a0f3638030`: 3 breaking, 7 warning, 44 info ## Changes - **2026-10-30** `db779c2e7b5f`: 1 breaking, 6 info - the `error` response's property type changed from no type to `object` for status `404` - added the optional property `error/details` to the response with the `404` status - added `#/components/schemas/ThreadAlreadyContinuedErrorDetails, #/components/schemas/ThreadContinueInFlightErrorDetails, #/components/schemas/ThreadFingerprintMismatchErrorDetails, #/components/schemas/ThreadUnsupportedRequestErrorDetails` to the `error/details` response property `anyOf` list for the response status `400` - removed discriminator from `error` response property for the response status `404` - removed `#/components/schemas/InvalidRequestError, #/components/schemas/AuthenticationError, #/components/schemas/BillingError, #/components/schemas/PermissionError, #/components/schemas/NotFoundError, #/components/schemas/RateLimitError, #/components/schemas/GatewayTimeoutError, #/components/schemas/APIError, #/components/schemas/OverloadedError` from the `error` response property `oneOf` list for the response status `404` - added the required property `error/message` to the response with the `404` status - added the required property `error/type` to the response with the `404` status - **2026-10-21** `94c83daca660`: 1 breaking, 5 warning, 2 info - the `messages/items/` request property type changed from `object` to no type - removed the request property `messages/items/content` - removed the request property `messages/items/role` - removed the request property `temperature` - removed the request property `top_k` - removed the request property `top_p` - added `assistant, system, user` discriminator mapping keys to the `messages/items/` request property - added `#/components/schemas/UserInputMessage, #/components/schemas/AssistantInputMessage, #/components/schemas/SystemInputMessage` to the `messages/items/` request property `oneOf` list - **2026-10-17** `bfa6803cbf21`: 1 breaking, 5 info - the `error` response's property type changed from no type to `object` for status `503` - added the optional property `error/details` to the response with the `503` status - removed discriminator from `error` response property for the response status `503` - removed `#/components/schemas/InvalidRequestError, #/components/schemas/AuthenticationError, #/components/schemas/BillingError, #/components/schemas/PermissionError, #/components/schemas/NotFoundError, #/components/schemas/RateLimitError, #/components/schemas/GatewayTimeoutError, #/components/schemas/APIError, #/components/schemas/OverloadedError` from the `error` response property `oneOf` list for the response status `503` - added the required property `error/message` to the response with the `503` status - added the required property `error/type` to the response with the `503` status - **2026-10-14** `569b1fb6ea2e`: 2 info - added the new optional request property `speed` - added the required property `usage/speed` to the response with the `200` status - **2026-10-09** `ee978b5e1294`: 1 breaking, 3 info - removed `subschema #15, subschema #16` from the `model` request property `anyOf` list - added `subschema #15, subschema #16` to the `model` request property `anyOf` list - added `subschema #15, subschema #16` to the `model` response property `anyOf` list for the response status `200` - removed `subschema #15, subschema #16` from the `model` response property `anyOf` list for the response status `200` - **2026-10-08** `5b6f4c063051`: 5 breaking, 25 info - the `error` response's property type changed from no type to `object` for status `400` - the `error` response's property type changed from no type to `object` for status `409` - the `error` response's property type changed from no type to `object` for status `413` - the `error` response's property type changed from no type to `object` for status `429` - the `error` response's property type changed from no type to `object` for status `529` - added the optional property `error/details` to the response with the `400` status - added the optional property `error/details` to the response with the `409` status - added the optional property `error/details` to the response with the `413` status - added the optional property `error/details` to the response with the `429` status - added the optional property `error/details` to the response with the `529` status - removed discriminator from `error` response property for the response status `400` - removed discriminator from `error` response property for the response status `409` - removed discriminator from `error` response property for the response status `413` - removed discriminator from `error` response property for the response status `429` - removed discriminator from `error` response property for the response status `529` - removed `#/components/schemas/InvalidRequestError, #/components/schemas/AuthenticationError, #/components/schemas/BillingError, #/components/schemas/PermissionError, #/components/schemas/NotFoundError, #/components/schemas/RateLimitError, #/components/schemas/GatewayTimeoutError, #/components/schemas/APIError, #/components/schemas/OverloadedError` from the `error` response property `oneOf` list for the response status `400` - removed `#/components/schemas/InvalidRequestError, #/components/schemas/AuthenticationError, #/components/schemas/BillingError, #/components/schemas/PermissionError, #/components/schemas/NotFoundError, #/components/schemas/RateLimitError, #/components/schemas/GatewayTimeoutError, #/components/schemas/APIError, #/components/schemas/OverloadedError` from the `error` response property `oneOf` list for the response status `409` - removed `#/components/schemas/InvalidRequestError, #/components/schemas/AuthenticationError, #/components/schemas/BillingError, #/components/schemas/PermissionError, #/components/schemas/NotFoundError, #/components/schemas/RateLimitError, #/components/schemas/GatewayTimeoutError, #/components/schemas/APIError, #/components/schemas/OverloadedError` from the `error` response property `oneOf` list for the response status `413` - removed `#/components/schemas/InvalidRequestError, #/components/schemas/AuthenticationError, #/components/schemas/BillingError, #/components/schemas/PermissionError, #/components/schemas/NotFoundError, #/components/schemas/RateLimitError, #/components/schemas/GatewayTimeoutError, #/components/schemas/APIError, #/components/schemas/OverloadedError` from the `error` response property `oneOf` list for the response status `429` - removed `#/components/schemas/InvalidRequestError, #/components/schemas/AuthenticationError, #/components/schemas/BillingError, #/components/schemas/PermissionError, #/components/schemas/NotFoundError, #/components/schemas/RateLimitError, #/components/schemas/GatewayTimeoutError, #/components/schemas/APIError, #/components/schemas/OverloadedError` from the `error` response property `oneOf` list for the response status `529` - added the required property `error/message` to the response with the `400` status - added the required property `error/message` to the response with the `409` status - added the required property `error/message` to the response with the `413` status - added the required property `error/message` to the response with the `429` status - added the required property `error/message` to the response with the `529` status - added the required property `error/type` to the response with the `400` status - added the required property `error/type` to the response with the `409` status - added the required property `error/type` to the response with the `413` status - added the required property `error/type` to the response with the `429` status - added the required property `error/type` to the response with the `529` status - **2026-10-07** `2705c258c5dc`: 2 info - added `subschema #1` to the `model` request property `anyOf` list - added `subschema #1` to the `model` response property `anyOf` list for the response status `200` - **2026-09-30** `d721a6487a16`: 1 breaking, 3 info - removed `subschema #18, subschema #19` from the `model` request property `anyOf` list - added `subschema #18, subschema #19` to the `model` request property `anyOf` list - added `subschema #18, subschema #19` to the `model` response property `anyOf` list for the response status `200` - removed `subschema #18, subschema #19` from the `model` response property `anyOf` list for the response status `200` - **2026-09-28** `3cd29369f196`: 1 breaking, 3 info - removed `subschema #4` from the `model` request property `anyOf` list - added `subschema #1, subschema #5` to the `model` request property `anyOf` list - added `subschema #1, subschema #5` to the `model` response property `anyOf` list for the response status `200` - removed `subschema #4` from the `model` response property `anyOf` list for the response status `200` - **2026-09-28** `36794f5ab00f`: 2 info - added `between_tools` discriminator mapping keys to the `thinking` request property - added `#/components/schemas/ThinkingConfigBetweenTools` to the `thinking` request property `oneOf` list - **2026-09-28** `231c3ffb9f5c`: 2 info - added the new optional request property `diagnostics` - added the required property `diagnostics` to the response with the `200` status - **2026-09-28** `86153a702615`: 1 breaking, 6 info - the `stop_details/anyOf[subschema #1: RefusalStopDetails]/category/anyOf[subschema #1: RefusalCategory]/` response's property type changed from `string` to no type for status `200` - added `subschema #1, subschema #2, subschema #3, subschema #4, subschema #5` to the `stop_details/anyOf[subschema #1: RefusalStopDetails]/category/anyOf[subschema #1: RefusalCategory]/` response property `anyOf` list for the response status `200` - removed the `bio` enum value from the `stop_details/anyOf[subschema #1: RefusalStopDetails]/category/anyOf[subschema #1: RefusalCategory]/` response property for the response status `200` - removed the `cyber` enum value from the `stop_details/anyOf[subschema #1: RefusalStopDetails]/category/anyOf[subschema #1: RefusalCategory]/` response property for the response status `200` - removed the `frontier_llm` enum value from the `stop_details/anyOf[subschema #1: RefusalStopDetails]/category/anyOf[subschema #1: RefusalCategory]/` response property for the response status `200` - removed the `general_harms` enum value from the `stop_details/anyOf[subschema #1: RefusalStopDetails]/category/anyOf[subschema #1: RefusalCategory]/` response property for the response status `200` - removed the `reasoning_extraction` enum value from the `stop_details/anyOf[subschema #1: RefusalStopDetails]/category/anyOf[subschema #1: RefusalCategory]/` response property for the response status `200` - **2026-09-22** `257523f5aeb5`: 2 info - added `subschema #3` to the `model` request property `anyOf` list - added `subschema #3` to the `model` response property `anyOf` list for the response status `200` - **2026-09-15** `3449c49f2da8`: 4 info - added the new optional request property `tools/items/oneOf[subschema #14: WebFetchTool_20250910]/url_sources` - added the new optional request property `tools/items/oneOf[subschema #16: WebFetchTool_20260209]/url_sources` - added the new optional request property `tools/items/oneOf[subschema #17: WebFetchTool_20260309]/url_sources` - added the new optional request property `tools/items/oneOf[subschema #19: WebFetchTool_20260318]/url_sources` - **2026-09-10** `e46a40fc336b`: 1 warning, 1 info - added the new `content_too_large` enum value to the `content/items/oneOf[subschema #7: ResponseWebFetchToolResultBlock]/content/anyOf[subschema #1: ResponseWebFetchToolResultError]/error_code` response property for the response status `200` - added the new `content_too_large` enum value to the request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #11: RequestWebFetchToolResultBlock]/content/anyOf[subschema #1: RequestWebFetchToolResultError]/error_code` - **2026-09-04** `e2857e722bed`: 1 breaking - the `content/items/oneOf[subschema #1: ResponseTextBlock]/text` response property's maxLength was unset from `5000000` for the response status `200` - **2026-09-04** `4789294140a2`: 17 info - added the new optional `header` request parameter `anthropic-workspace-id` - added the non-success response with the status `400` - added the non-success response with the status `401` - added the non-success response with the status `403` - added the non-success response with the status `404` - added the non-success response with the status `408` - added the non-success response with the status `409` - added the non-success response with the status `412` - added the non-success response with the status `413` - added the non-success response with the status `429` - added the non-success response with the status `431` - added the non-success response with the status `499` - added the non-success response with the status `500` - added the non-success response with the status `501` - added the non-success response with the status `503` - added the non-success response with the status `504` - added the non-success response with the status `529` - **2026-09-01** `d1d189d791d1`: 2 warning, 2 info - removed the request property `tools/items/oneOf[subschema #7: BrowserToolset_20260801]/allowed_callers` - removed the request property `tools/items/oneOf[subschema #9: ComputerToolset_20260801]/allowed_callers` - added `subschema #2, subschema #3` to the `model` request property `anyOf` list - added `subschema #2, subschema #3` to the `model` response property `anyOf` list for the response status `200` - **2026-08-19** `67ee007cda1c`: 29 info - added the new optional request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #11: RequestWebFetchToolResultBlock]/content/anyOf[subschema #2: RequestWebFetchResultBlock]/content/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #2: RequestImageBlock]/transformations` - added the new optional request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #2: RequestImageBlock]/transformations` - added the new optional request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #3: RequestDocumentBlock]/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #2: RequestImageBlock]/transformations` - added the new optional request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #7: RequestToolUseBlock]/toolset_name` - added the new optional request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #2: RequestImageBlock]/transformations` - added the new optional request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #4: RequestDocumentBlock]/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #2: RequestImageBlock]/transformations` - added the new optional request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/toolset_name` - added `#/components/schemas/ContainerParams` to the `container` request property `anyOf` list - added `browser_state` discriminator mapping keys to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/` request property - added `file` discriminator mapping keys to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #11: RequestWebFetchToolResultBlock]/content/anyOf[subschema #2: RequestWebFetchResultBlock]/content/source` request property - added `file` discriminator mapping keys to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #11: RequestWebFetchToolResultBlock]/content/anyOf[subschema #2: RequestWebFetchResultBlock]/content/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #2: RequestImageBlock]/source` request property - added `file` discriminator mapping keys to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #2: RequestImageBlock]/source` request property - added `file` discriminator mapping keys to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #3: RequestDocumentBlock]/source` request property - added `file` discriminator mapping keys to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #3: RequestDocumentBlock]/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #2: RequestImageBlock]/source` request property - added `file` discriminator mapping keys to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #2: RequestImageBlock]/source` request property - added `file` discriminator mapping keys to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #4: RequestDocumentBlock]/source` request property - added `file` discriminator mapping keys to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #4: RequestDocumentBlock]/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #2: RequestImageBlock]/source` request property - added `#/components/schemas/BrowserToolset_20260801, #/components/schemas/ComputerToolset_20260801` to the `tools/items/` request property `oneOf` list - added `#/components/schemas/FileDocumentSource` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #11: RequestWebFetchToolResultBlock]/content/anyOf[subschema #2: RequestWebFetchResultBlock]/content/source` request property `oneOf` list - added `#/components/schemas/FileDocumentSource` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #3: RequestDocumentBlock]/source` request property `oneOf` list - added `#/components/schemas/FileDocumentSource` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #4: RequestDocumentBlock]/source` request property `oneOf` list - added `#/components/schemas/FileImageSource` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #11: RequestWebFetchToolResultBlock]/content/anyOf[subschema #2: RequestWebFetchResultBlock]/content/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #2: RequestImageBlock]/source` request property `oneOf` list - added `#/components/schemas/FileImageSource` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #2: RequestImageBlock]/source` request property `oneOf` list - added `#/components/schemas/FileImageSource` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #3: RequestDocumentBlock]/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #2: RequestImageBlock]/source` request property `oneOf` list - added `#/components/schemas/FileImageSource` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #2: RequestImageBlock]/source` request property `oneOf` list - added `#/components/schemas/FileImageSource` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #4: RequestDocumentBlock]/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #2: RequestImageBlock]/source` request property `oneOf` list - added `#/components/schemas/RequestBrowserStateBlock` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/` request property `oneOf` list - added the optional property `content/items/oneOf[subschema #4: ResponseToolUseBlock]/toolset_name` to the response with the `200` status - added the required property `container/anyOf[subschema #1: Container]/skills` to the response with the `200` status - **2026-08-19** `e9d8152420c3`: 1 breaking, 1 info - removed `#/components/schemas/RequestMidConvSystemBlock` from the `messages/items/content/anyOf[subschema #2]/items/` request property `oneOf` list - removed `mid_conv_system` discriminator mapping keys from the `messages/items/content/anyOf[subschema #2]/items/` request property - **2026-08-13** `6e9020ec2b41`: 27 info - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #11: RequestWebFetchToolResultBlock]/content/anyOf[subschema #2: RequestWebFetchResultBlock]/content/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #1: RequestCharLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #11: RequestWebFetchToolResultBlock]/content/anyOf[subschema #2: RequestWebFetchResultBlock]/content/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #2: RequestPageLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #11: RequestWebFetchToolResultBlock]/content/anyOf[subschema #2: RequestWebFetchResultBlock]/content/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #3: RequestContentBlockLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #17: RequestMidConvSystemBlock]/content/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #1: RequestCharLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #17: RequestMidConvSystemBlock]/content/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #2: RequestPageLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #17: RequestMidConvSystemBlock]/content/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #3: RequestContentBlockLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #1: RequestCharLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #2: RequestPageLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #3: RequestContentBlockLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #3: RequestDocumentBlock]/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #1: RequestCharLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #3: RequestDocumentBlock]/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #2: RequestPageLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #3: RequestDocumentBlock]/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #3: RequestContentBlockLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #4: RequestSearchResultBlock]/content/items/citations/anyOf[subschema #1]/items/oneOf[subschema #1: RequestCharLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #4: RequestSearchResultBlock]/content/items/citations/anyOf[subschema #1]/items/oneOf[subschema #2: RequestPageLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #4: RequestSearchResultBlock]/content/items/citations/anyOf[subschema #1]/items/oneOf[subschema #3: RequestContentBlockLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #1: RequestCharLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #2: RequestPageLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #3: RequestContentBlockLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #3: RequestSearchResultBlock]/content/items/citations/anyOf[subschema #1]/items/oneOf[subschema #1: RequestCharLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #3: RequestSearchResultBlock]/content/items/citations/anyOf[subschema #1]/items/oneOf[subschema #2: RequestPageLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #3: RequestSearchResultBlock]/content/items/citations/anyOf[subschema #1]/items/oneOf[subschema #3: RequestContentBlockLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #4: RequestDocumentBlock]/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #1: RequestCharLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #4: RequestDocumentBlock]/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #2: RequestPageLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #8: RequestToolResultBlock]/content/anyOf[subschema #2]/items/oneOf[subschema #4: RequestDocumentBlock]/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: content_block_source_content]/items/oneOf[subschema #1: RequestTextBlock]/citations/anyOf[subschema #1]/items/oneOf[subschema #3: RequestContentBlockLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `system/anyOf[subschema #2]/items/citations/anyOf[subschema #1]/items/oneOf[subschema #1: RequestCharLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `system/anyOf[subschema #2]/items/citations/anyOf[subschema #1]/items/oneOf[subschema #2: RequestPageLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - the `system/anyOf[subschema #2]/items/citations/anyOf[subschema #1]/items/oneOf[subschema #3: RequestContentBlockLocationCitation]/document_title/anyOf[subschema #1]/` request property's maxLength was increased from `255` to `500` - **2026-08-07** `538e9bd0db77`: 1 breaking, 1 info - removed `subschema #17, subschema #18` from the `model` request property `anyOf` list - removed `subschema #17, subschema #18` from the `model` response property `anyOf` list for the response status `200` - **2026-07-24** `a97790bd7f18`: 1 breaking, 3 info - removed `subschema #5, subschema #6, subschema #8, subschema #12, subschema #13, subschema #16, subschema #17` from the `model` request property `anyOf` list - added `subschema #5, subschema #6, subschema #7, subschema #9, subschema #13, subschema #14, subschema #17, subschema #18` to the `model` request property `anyOf` list - added `subschema #5, subschema #6, subschema #7, subschema #9, subschema #13, subschema #14, subschema #17, subschema #18` to the `model` response property `anyOf` list for the response status `200` - removed `subschema #5, subschema #6, subschema #8, subschema #12, subschema #13, subschema #16, subschema #17` from the `model` response property `anyOf` list for the response status `200` - **2026-07-23** `d7893c708340`: 1 warning - added the new `model_context_window_exceeded` enum value to the `stop_reason/anyOf[#/components/schemas/StopReason]/` response property for the response status `200` - **2026-07-21** `97200025c28e`: 1 warning - added the new `general_harms` enum value to the `stop_details/anyOf[subschema #1: RefusalStopDetails]/category/anyOf[subschema #1: RefusalCategory]/` response property for the response status `200` - **2026-07-01** `9c991bee394d`: 1 info - removed the `military_weapons` enum value from the `stop_details/anyOf[subschema #1: RefusalStopDetails]/category/anyOf[subschema #1: RefusalCategory]/` response property for the response status `200` - **2026-06-30** `7caa9a75ddbc`: 2 info - added `subschema #2` to the `model` request property `anyOf` list - added `subschema #2` to the `model` response property `anyOf` list for the response status `200` - **2026-06-29** `4465f98f96c1`: 1 info - added `#/components/schemas/WebSearchTool_20260318, #/components/schemas/WebFetchTool_20260318` to the `tools/items/` request property `oneOf` list - **2026-06-24** `82c21eb736c8`: 1 warning, 1 info - added the new `military_weapons` enum value to the `stop_details/anyOf[subschema #1: RefusalStopDetails]/category/anyOf[subschema #1: RefusalCategory]/` response property for the response status `200` - added the new optional `header` request parameter `anthropic-user-profile-id` - **2026-06-18** `063bcb9d6cf9`: 1 breaking, 18 info - removed `subschema #17, subschema #18, subschema #19, subschema #20, subschema #21` from the `model` request property `anyOf` list - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #10: WebSearchTool_20250305 -> subschema #11: WebSearchTool_20250305]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #11: WebFetchTool_20250910 -> subschema #12: WebFetchTool_20250910]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #12: WebSearchTool_20260209 -> subschema #13: WebSearchTool_20260209]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #13: WebFetchTool_20260209 -> subschema #14: WebFetchTool_20260209]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #14: WebFetchTool_20260309 -> subschema #15: WebFetchTool_20260309]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #15: ToolSearchToolBM25_20251119 -> subschema #16: ToolSearchToolBM25_20251119]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #16: ToolSearchToolRegex_20251119 -> subschema #17: ToolSearchToolRegex_20251119]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #1: Tool]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #2: BashTool_20250124]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #3: CodeExecutionTool_20250522]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #4: CodeExecutionTool_20250825]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #5: CodeExecutionTool_20260120]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #6: MemoryTool_20250818 -> subschema #7: MemoryTool_20250818]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #7: TextEditor_20250124 -> subschema #8: TextEditor_20250124]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #8: TextEditor_20250429 -> subschema #9: TextEditor_20250429]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #9: TextEditor_20250728 -> subschema #10: TextEditor_20250728]/allowed_callers/items/` - added `#/components/schemas/CodeExecutionTool_20260521` to the `tools/items/` request property `oneOf` list - removed `subschema #17, subschema #18, subschema #19, subschema #20, subschema #21` from the `model` response property `anyOf` list for the response status `200` - **2026-06-09** `996eb28b2ab6`: 1 warning - added the new `frontier_llm` enum value to the `stop_details/anyOf[subschema #1: RefusalStopDetails]/category/anyOf[subschema #1]/` response property for the response status `200` - **2026-06-09** `00259327305f`: 1 breaking, 1 warning, 3 info - removed `subschema #4` from the `model` request property `anyOf` list - added the new `reasoning_extraction` enum value to the `stop_details/anyOf[subschema #1: RefusalStopDetails]/category/anyOf[subschema #1]/` response property for the response status `200` - added `subschema #2, subschema #3, subschema #6` to the `model` request property `anyOf` list - added `subschema #2, subschema #3, subschema #6` to the `model` response property `anyOf` list for the response status `200` - removed `subschema #4` from the `model` response property `anyOf` list for the response status `200` - **2026-06-06** `546c704d347b`: 1 breaking, 4 info - removed `subschema #13, subschema #14` from the `model` request property `anyOf` list - added the new optional request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #15: RequestToolSearchToolResultBlock]/content/anyOf[subschema #1: RequestToolSearchToolResultError]/error_message` - added `subschema #13, subschema #14` to the `model` request property `anyOf` list - added `subschema #13, subschema #14` to the `model` response property `anyOf` list for the response status `200` - removed `subschema #13, subschema #14` from the `model` response property `anyOf` list for the response status `200` - **2026-05-28** `f9d488f9290d`: 1 warning, 7 info - added the new `url_not_in_prior_context` enum value to the `content/items/oneOf[subschema #7: ResponseWebFetchToolResultBlock]/content/anyOf[subschema #1: ResponseWebFetchToolResultError]/error_code` response property for the response status `200` - added `subschema #2` to the `model` request property `anyOf` list - added `mid_conv_system` discriminator mapping keys to the `messages/items/content/anyOf[subschema #2]/items/` request property - added the new `system` enum value to the request property `messages/items/role` - added the new `url_not_in_prior_context` enum value to the request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #11: RequestWebFetchToolResultBlock]/content/anyOf[subschema #1: RequestWebFetchToolResultError]/error_code` - added `#/components/schemas/RequestMidConvSystemBlock` to the `messages/items/content/anyOf[subschema #2]/items/` request property `oneOf` list - added `subschema #2` to the `model` response property `anyOf` list for the response status `200` - added the required property `usage/output_tokens_details` to the response with the `200` status - **2026-05-06** `a4186730f56c`: 1 breaking - the `tools/items/oneOf[subschema #9: TextEditor_20250728]/input_examples/items/additionalProperties/` request property type changed from `unknown` to no type - **2026-04-30** `6edc6519fd32`: 1 breaking, 1 info - the `tools/items/oneOf[subschema #9: TextEditor_20250728]/input_examples/items/additionalProperties/` request property type changed from no type to `unknown` - the `max_tokens` request property's min was decreased from `1.00` to `0.00` - **2026-04-16** `e0696f59ae07`: 1 breaking, 4 info - removed `subschema #13, subschema #14, subschema #15, subschema #16` from the `model` request property `anyOf` list - added `subschema #2, subschema #14, subschema #15, subschema #16, subschema #17` to the `model` request property `anyOf` list - added the new `xhigh` enum value to the request property `output_config/effort/anyOf[subschema #1: EffortLevel]/` - added `subschema #2, subschema #14, subschema #15, subschema #16, subschema #17` to the `model` response property `anyOf` list for the response status `200` - removed `subschema #13, subschema #14, subschema #15, subschema #16` from the `model` response property `anyOf` list for the response status `200` - **2026-04-08** `69486316563e`: 1 breaking, 6 info - removed `subschema #2` from the `model` request property `anyOf` list - added `subschema #2, subschema #3` to the `model` request property `anyOf` list - request property `temperature` deprecated - request property `top_k` deprecated - request property `top_p` deprecated - added `subschema #2, subschema #3` to the `model` response property `anyOf` list for the response status `200` - removed `subschema #2` from the `model` response property `anyOf` list for the response status `200` - **2026-04-01** `efe26b096126`: 1 info - added the required property `stop_details` to the response with the `200` status - **2026-03-18** `dd2dcd00a757`: 1 info - the `metadata/user_id/anyOf[subschema #1]/` request property's maxLength was increased from `256` to `512` - **2026-03-16** `7fce94a3c9f7`: 1 breaking, 6 info - removed `subschema #3, subschema #6, subschema #7, subschema #8, subschema #9, subschema #10, subschema #11, subschema #14, subschema #15, subschema #16, subschema #17, subschema #18, subschema #19, subschema #20, subschema #21, subschema #22, subschema #23` from the `model` request property `anyOf` list - added the new optional request property `thinking/oneOf[subschema #1: ThinkingConfigEnabled]/display` - added the new optional request property `thinking/oneOf[subschema #3: ThinkingConfigAdaptive]/display` - added `subschema #3, subschema #4, subschema #5, subschema #8, subschema #9, subschema #10, subschema #11, subschema #12, subschema #13, subschema #16` to the `model` request property `anyOf` list - added `#/components/schemas/WebFetchTool_20260309` to the `tools/items/` request property `oneOf` list - added `subschema #3, subschema #4, subschema #5, subschema #8, subschema #9, subschema #10, subschema #11, subschema #12, subschema #13, subschema #16` to the `model` response property `anyOf` list for the response status `200` - removed `subschema #3, subschema #6, subschema #7, subschema #8, subschema #9, subschema #10, subschema #11, subschema #14, subschema #15, subschema #16, subschema #17, subschema #18, subschema #19, subschema #20, subschema #21, subschema #22, subschema #23` from the `model` response property `anyOf` list for the response status `200` - **2026-02-19** `29a6b7ba5194`: 1 info - added the new optional request property `cache_control` - **2026-02-18** `5387c517ad6a`: 15 info - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #10: WebSearchTool_20250305]/allowed_callers/items/` - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #11: WebFetchTool_20250910]/allowed_callers/items/` - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #12: WebSearchTool_20260209]/allowed_callers/items/` - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #13: WebFetchTool_20260209]/allowed_callers/items/` - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #14: ToolSearchToolBM25_20251119]/allowed_callers/items/` - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #15: ToolSearchToolRegex_20251119]/allowed_callers/items/` - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #1: Tool]/allowed_callers/items/` - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #2: BashTool_20250124]/allowed_callers/items/` - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #3: CodeExecutionTool_20250522]/allowed_callers/items/` - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #4: CodeExecutionTool_20250825]/allowed_callers/items/` - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #5: CodeExecutionTool_20260120]/allowed_callers/items/` - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #6: MemoryTool_20250818]/allowed_callers/items/` - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #7: TextEditor_20250124]/allowed_callers/items/` - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #8: TextEditor_20250429]/allowed_callers/items/` - added the new `code_execution_20260120` enum value to the request property `tools/items/oneOf[subschema #9: TextEditor_20250728]/allowed_callers/items/` - **2026-02-17** `6924f88807cb`: 1 breaking, 1 warning - removed the required property `usage/speed` from the response with the `200` status - removed the request property `speed` - …earlier changes are on the page: https://skmtc.dev/anthropics/apis/anthropic-api/changes/v1/messages/post --- [Operation](https://skmtc.dev/anthropics/apis/anthropic-api/docs/v1/messages/post.md) - [API](https://skmtc.dev/anthropics/apis/anthropic-api.md) - [Page](https://skmtc.dev/anthropics/apis/anthropic-api/changes/v1/messages/post)