--- title: "Changes to Create a Message" method: POST path: "/v1/messages?beta=true" --- # Changes to Create a Message `POST /v1/messages?beta=true` > Every recorded change to this endpoint, newest first. ## Timeline Changed in 30 of 68 revisions. - **2026-09-01** `d1d189d791d1` — 2 warning, 18 info - **2026-08-25** `dca67b3e5234` — 4 info - **2026-08-19** `67ee007cda1c` — 11 info - **2026-08-14** `e9d8152420c3` — 1 breaking, 1 info - **2026-08-13** `6e9020ec2b41` — 30 info - **2026-08-06** `538e9bd0db77` — 5 breaking, 6 info - **2026-07-24** `a97790bd7f18` — 4 breaking, 23 info - **2026-07-21** `97200025c28e` — 2 warning - **2026-07-01** `9c991bee394d` — 2 info - **2026-06-30** `7caa9a75ddbc` — 11 info - **2026-06-29** `4465f98f96c1` — 1 info - **2026-06-24** `82c21eb736c8` — 3 warning, 1 info - **2026-06-18** `063bcb9d6cf9` — 5 breaking, 31 info - **2026-06-09** `996eb28b2ab6` — 1 warning - **2026-06-09** `00259327305f` — 4 breaking, 1 warning, 16 info - **2026-06-06** `546c704d347b` — 2 breaking, 1 warning, 9 info - **2026-05-28** `f9d488f9290d` — 1 warning, 13 info - **2026-05-19** `40e330aba8bc` — 1 info - **2026-05-13** `400ce646c6b2` — 2 info - **2026-04-30** `6edc6519fd32` — 1 info - **2026-04-16** `e0696f59ae07` — 2 breaking, 11 info - **2026-04-09** `d87d3ef6f636` — 2 breaking, 1 warning, 6 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` — 2 breaking, 8 info - **2026-02-19** `29a6b7ba5194` — 1 info - **2026-02-18** `5387c517ad6a` — 20 info - **2026-02-17** `53a0f3638030` — 2 breaking, 15 info - **2026-02-07** `fee5dc365a49` — 2 info ## Changes - **2026-09-01** `d1d189d791d1` — 2 warning, 18 info - removed the request property `tools/items/oneOf[subschema #14: ComputerToolset_20260801]/allowed_callers` - removed the request property `tools/items/oneOf[subschema #8: BrowserToolset_20260801]/allowed_callers` - added the new optional request property `fallbacks/anyOf[subschema #1]/items/thinking/anyOf[subschema #1]/oneOf[subschema #1: ThinkingConfigEnabled]/block_binding` - added the new optional request property `fallbacks/anyOf[subschema #1]/items/thinking/anyOf[subschema #1]/oneOf[subschema #3: ThinkingConfigAdaptive]/block_binding` - added the new optional request property `messages/items/clear_at` - added the new optional request property `messages/items/output_config` - added the new optional request property `thinking/oneOf[subschema #1: ThinkingConfigEnabled]/block_binding` - added the new optional request property `thinking/oneOf[subschema #3: ThinkingConfigAdaptive]/block_binding` - added `subschema #2, subschema #3` to the `fallbacks/anyOf[subschema #1]/items/model` request property `anyOf` list - added `subschema #2, subschema #3` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #23: RequestFallbackBlock]/from/model` request property `anyOf` list - added `subschema #2, subschema #3` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #23: RequestFallbackBlock]/to/model` request property `anyOf` list - added `subschema #2, subschema #3` to the `model` request property `anyOf` list - added `subschema #2, subschema #3` to the `tools/items/oneOf[subschema #25: AdvisorTool_20260301]/model` request property `anyOf` list - added the optional property `input_transformations` to the response with the `200` status - added `subschema #2, subschema #3` to the `content/items/oneOf[subschema #17: ResponseFallbackBlock]/from/model` response property `anyOf` list for the response status `200` - added `subschema #2, subschema #3` to the `content/items/oneOf[subschema #17: ResponseFallbackBlock]/to/model` response property `anyOf` list for the response status `200` - added `subschema #2, subschema #3` to the `model` response property `anyOf` list for the response status `200` - added `subschema #2, subschema #3` to the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #1: MessageIterationUsage]/model` response property `anyOf` list for the response status `200` - added `subschema #2, subschema #3` to the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #3: AdvisorMessageIterationUsage]/model` response property `anyOf` list for the response status `200` - added `subschema #2, subschema #3` to the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #4: FallbackMessageIterationUsage]/model` response property `anyOf` list for the response status `200` - **2026-08-25** `dca67b3e5234` — 4 info - added the new `updates` enum value to the request property `fallbacks/anyOf[subschema #1]/items/thinking/anyOf[subschema #1]/oneOf[subschema #1: ThinkingConfigEnabled]/display/anyOf[subschema #1: ThinkingDisplayMode]/` - added the new `updates` enum value to the request property `fallbacks/anyOf[subschema #1]/items/thinking/anyOf[subschema #1]/oneOf[subschema #3: ThinkingConfigAdaptive]/display/anyOf[subschema #1: ThinkingDisplayMode]/` - added the new `updates` enum value to the request property `thinking/oneOf[subschema #1: ThinkingConfigEnabled]/display/anyOf[subschema #1: ThinkingDisplayMode]/` - added the new `updates` enum value to the request property `thinking/oneOf[subschema #3: ThinkingConfigAdaptive]/display/anyOf[subschema #1: ThinkingDisplayMode]/` - **2026-08-19** `67ee007cda1c` — 11 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: beta_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: beta_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: beta_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 `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 `#/components/schemas/BetaBrowserToolset_20260801, #/components/schemas/BetaComputerToolset_20260801` to the `tools/items/` request property `oneOf` list - added `#/components/schemas/BetaRequestBrowserStateBlock` 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 - **2026-08-14** `e9d8152420c3` — 1 breaking, 1 info - removed `#/components/schemas/BetaRequestMidConvSystemBlock` 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` — 30 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: beta_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: beta_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: beta_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 #18: RequestMCPToolResultBlock]/content/anyOf[subschema #2: beta_mcp_tool_result_block_param_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 #18: RequestMCPToolResultBlock]/content/anyOf[subschema #2: beta_mcp_tool_result_block_param_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 #18: RequestMCPToolResultBlock]/content/anyOf[subschema #2: beta_mcp_tool_result_block_param_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 #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 #21: 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 #21: 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 #21: 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 #3: RequestDocumentBlock]/source/oneOf[subschema #3: ContentBlockSource]/content/anyOf[subschema #2: beta_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: beta_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: beta_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: beta_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: beta_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: beta_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` - **2026-08-06** `538e9bd0db77` — 5 breaking, 6 info - removed `subschema #17, subschema #18` from the `fallbacks/anyOf[subschema #1]/items/model` request property `anyOf` list - removed `subschema #17, subschema #18` from the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #24: RequestFallbackBlock]/from/model` request property `anyOf` list - removed `subschema #17, subschema #18` from the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #24: RequestFallbackBlock]/to/model` request property `anyOf` list - removed `subschema #17, subschema #18` from the `model` request property `anyOf` list - removed `subschema #17, subschema #18` from the `tools/items/oneOf[subschema #23: AdvisorTool_20260301]/model` request property `anyOf` list - removed `subschema #17, subschema #18` from the `content/items/oneOf[subschema #17: ResponseFallbackBlock]/from/model` response property `anyOf` list for the response status `200` - removed `subschema #17, subschema #18` from the `content/items/oneOf[subschema #17: ResponseFallbackBlock]/to/model` response property `anyOf` list for the response status `200` - removed `subschema #17, subschema #18` from the `model` response property `anyOf` list for the response status `200` - removed `subschema #17, subschema #18` from the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #1: MessageIterationUsage]/model` response property `anyOf` list for the response status `200` - removed `subschema #17, subschema #18` from the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #3: AdvisorMessageIterationUsage]/model` response property `anyOf` list for the response status `200` - removed `subschema #17, subschema #18` from the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #4: FallbackMessageIterationUsage]/model` response property `anyOf` list for the response status `200` - **2026-07-24** `a97790bd7f18` — 4 breaking, 23 info - removed `subschema #5, subschema #6, subschema #8, subschema #12, subschema #13, subschema #16, subschema #17` from the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #22: RequestFallbackBlock -> subschema #24: RequestFallbackBlock]/from/model` request property `anyOf` list - removed `subschema #5, subschema #6, subschema #8, subschema #12, subschema #13, subschema #16, subschema #17` from the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #22: RequestFallbackBlock -> subschema #24: RequestFallbackBlock]/to/model` request property `anyOf` list - removed `subschema #5, subschema #6, subschema #8, subschema #12, subschema #13, subschema #16, subschema #17` from the `model` request property `anyOf` list - removed `subschema #5, subschema #6, subschema #8, subschema #12, subschema #13, subschema #16, subschema #17` from the `tools/items/oneOf[subschema #23: AdvisorTool_20260301]/model` request property `anyOf` list - added `#/components/schemas/BetaFallbackCreditTokenParam` to the `fallback_credit_token` request property `anyOf` list - added `subschema #5, subschema #6, subschema #7, subschema #9, subschema #13, subschema #14, subschema #17, subschema #18` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #22: RequestFallbackBlock -> subschema #24: RequestFallbackBlock]/from/model` request property `anyOf` list - added `subschema #5, subschema #6, subschema #7, subschema #9, subschema #13, subschema #14, subschema #17, subschema #18` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #22: RequestFallbackBlock -> subschema #24: RequestFallbackBlock]/to/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 `tools/items/oneOf[subschema #23: AdvisorTool_20260301]/model` request property `anyOf` list - added `tool_addition, tool_removal` discriminator mapping keys to the `messages/items/content/anyOf[subschema #2]/items/` request property - added `tool_addition, tool_removal` discriminator mapping keys to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #21: RequestMidConvSystemBlock]/content/items/` request property - request property `fallbacks` list-of-types was widened by adding types `string` to media type `application/json` - added `#/components/schemas/BetaRequestToolAdditionBlock, #/components/schemas/BetaRequestToolRemovalBlock` to the `messages/items/content/anyOf[subschema #2]/items/` request property `oneOf` list - added `#/components/schemas/BetaRequestToolAdditionBlock, #/components/schemas/BetaRequestToolRemovalBlock` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #21: RequestMidConvSystemBlock]/content/items/` request property `oneOf` list - added `subschema #5, subschema #6, subschema #7, subschema #9, subschema #13, subschema #14, subschema #17, subschema #18` to the `content/items/oneOf[subschema #17: ResponseFallbackBlock]/from/model` response property `anyOf` list for the response status `200` - added `subschema #5, subschema #6, subschema #7, subschema #9, subschema #13, subschema #14, subschema #17, subschema #18` to the `content/items/oneOf[subschema #17: ResponseFallbackBlock]/to/model` response property `anyOf` list for the response status `200` - 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` - added `subschema #5, subschema #6, subschema #7, subschema #9, subschema #13, subschema #14, subschema #17, subschema #18` to the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #1: MessageIterationUsage]/model` response property `anyOf` list for the response status `200` - added `subschema #5, subschema #6, subschema #7, subschema #9, subschema #13, subschema #14, subschema #17, subschema #18` to the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #3: AdvisorMessageIterationUsage]/model` response property `anyOf` list for the response status `200` - added `subschema #5, subschema #6, subschema #7, subschema #9, subschema #13, subschema #14, subschema #17, subschema #18` to the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #4: FallbackMessageIterationUsage]/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 `content/items/oneOf[subschema #17: ResponseFallbackBlock]/from/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 `content/items/oneOf[subschema #17: ResponseFallbackBlock]/to/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` - removed `subschema #5, subschema #6, subschema #8, subschema #12, subschema #13, subschema #16, subschema #17` from the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #1: MessageIterationUsage]/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 `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #3: AdvisorMessageIterationUsage]/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 `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #4: FallbackMessageIterationUsage]/model` response property `anyOf` list for the response status `200` - added the required property `usage/fallback_credit` to the response with the `200` status - **2026-07-21** `97200025c28e` — 2 warning - added the new `general_harms` enum value to the `content/items/oneOf[subschema #17: ResponseFallbackBlock]/trigger/category/anyOf[subschema #1: RefusalCategory]/` response property for the response status `200` - 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` — 2 info - removed the `military_weapons` enum value from the `content/items/oneOf[subschema #17: ResponseFallbackBlock]/trigger/category/anyOf[subschema #1: RefusalCategory]/` response property for the response status `200` - 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` — 11 info - added `subschema #2` to the `fallbacks/anyOf[subschema #1]/items/model` request property `anyOf` list - added `subschema #2` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #22: RequestFallbackBlock]/from/model` request property `anyOf` list - added `subschema #2` to the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #22: RequestFallbackBlock]/to/model` request property `anyOf` list - added `subschema #2` to the `model` request property `anyOf` list - added `subschema #2` to the `tools/items/oneOf[subschema #23: AdvisorTool_20260301]/model` request property `anyOf` list - added `subschema #2` to the `content/items/oneOf[subschema #17: ResponseFallbackBlock]/from/model` response property `anyOf` list for the response status `200` - added `subschema #2` to the `content/items/oneOf[subschema #17: ResponseFallbackBlock]/to/model` response property `anyOf` list for the response status `200` - added `subschema #2` to the `model` response property `anyOf` list for the response status `200` - added `subschema #2` to the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #1: MessageIterationUsage]/model` response property `anyOf` list for the response status `200` - added `subschema #2` to the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #3: AdvisorMessageIterationUsage]/model` response property `anyOf` list for the response status `200` - added `subschema #2` to the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #4: FallbackMessageIterationUsage]/model` response property `anyOf` list for the response status `200` - **2026-06-29** `4465f98f96c1` — 1 info - added `#/components/schemas/BetaWebSearchTool_20260318, #/components/schemas/BetaWebFetchTool_20260318` to the `tools/items/` request property `oneOf` list - **2026-06-24** `82c21eb736c8` — 3 warning, 1 info - removed the request property `user_profile_id` - added the new `military_weapons` enum value to the `content/items/oneOf[subschema #17: ResponseFallbackBlock]/trigger/category/anyOf[subschema #1: RefusalCategory]/` response property for the response status `200` - 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` — 5 breaking, 31 info - removed `subschema #17, subschema #18, subschema #19, subschema #20, subschema #21` from the `fallbacks/anyOf[subschema #1]/items/model` request property `anyOf` list - removed `subschema #17, subschema #18, subschema #19, subschema #20, subschema #21` from the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #22: RequestFallbackBlock]/from/model` request property `anyOf` list - removed `subschema #17, subschema #18, subschema #19, subschema #20, subschema #21` from the `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #22: RequestFallbackBlock]/to/model` request property `anyOf` list - removed `subschema #17, subschema #18, subschema #19, subschema #20, subschema #21` from the `model` request property `anyOf` list - removed `subschema #17, subschema #18, subschema #19, subschema #20, subschema #21` from the `tools/items/oneOf[subschema #20: AdvisorTool_20260301 -> subschema #21: AdvisorTool_20260301]/model` request property `anyOf` list - added the new optional request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #22: RequestFallbackBlock]/trigger` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #10: TextEditor_20241022 -> subschema #11: TextEditor_20241022]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #11: ComputerUseTool_20251124 -> subschema #12: ComputerUseTool_20251124]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #12: TextEditor_20250124 -> subschema #13: TextEditor_20250124]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #13: TextEditor_20250429 -> subschema #14: TextEditor_20250429]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #14: TextEditor_20250728 -> subschema #15: TextEditor_20250728]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #15: WebSearchTool_20250305 -> subschema #16: WebSearchTool_20250305]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #16: WebFetchTool_20250910 -> subschema #17: WebFetchTool_20250910]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #17: WebSearchTool_20260209 -> subschema #18: WebSearchTool_20260209]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #18: WebFetchTool_20260209 -> subschema #19: WebFetchTool_20260209]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #19: WebFetchTool_20260309 -> subschema #20: WebFetchTool_20260309]/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 #20: AdvisorTool_20260301 -> subschema #21: AdvisorTool_20260301]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #21: ToolSearchToolBM25_20251119 -> subschema #22: ToolSearchToolBM25_20251119]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #22: ToolSearchToolRegex_20251119 -> subschema #23: ToolSearchToolRegex_20251119]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #2: BashTool_20241022]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #3: BashTool_20250124]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #4: CodeExecutionTool_20250522]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #5: CodeExecutionTool_20250825]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #6: CodeExecutionTool_20260120]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #7: ComputerUseTool_20241022 -> subschema #8: ComputerUseTool_20241022]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #8: MemoryTool_20250818 -> subschema #9: MemoryTool_20250818]/allowed_callers/items/` - added the new `code_execution_20260521` enum value to the request property `tools/items/oneOf[subschema #9: ComputerUseTool_20250124 -> subschema #10: ComputerUseTool_20250124]/allowed_callers/items/` - added `#/components/schemas/BetaCodeExecutionTool_20260521` to the `tools/items/` request property `oneOf` list - removed `subschema #17, subschema #18, subschema #19, subschema #20, subschema #21` from the `content/items/oneOf[subschema #17: ResponseFallbackBlock]/from/model` response property `anyOf` list for the response status `200` - removed `subschema #17, subschema #18, subschema #19, subschema #20, subschema #21` from the `content/items/oneOf[subschema #17: ResponseFallbackBlock]/to/model` response property `anyOf` list for the response status `200` - removed `subschema #17, subschema #18, subschema #19, subschema #20, subschema #21` from the `model` response property `anyOf` list for the response status `200` - removed `subschema #17, subschema #18, subschema #19, subschema #20, subschema #21` from the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #1: MessageIterationUsage]/model` response property `anyOf` list for the response status `200` - removed `subschema #17, subschema #18, subschema #19, subschema #20, subschema #21` from the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #3: AdvisorMessageIterationUsage]/model` response property `anyOf` list for the response status `200` - removed `subschema #17, subschema #18, subschema #19, subschema #20, subschema #21` from the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #4: FallbackMessageIterationUsage]/model` response property `anyOf` list for the response status `200` - added the required property `content/items/oneOf[subschema #17: ResponseFallbackBlock]/trigger` to the response with the `200` status - **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` — 4 breaking, 1 warning, 16 info - removed `subschema #4` from the `model` request property `anyOf` list - removed `subschema #4` from the `tools/items/oneOf[subschema #20: AdvisorTool_20260301]/model` request property `anyOf` list - added `#/components/schemas/BetaFallbackMessageIterationUsage` to the `usage/iterations/anyOf[subschema #1]/items/` response property `oneOf` list for the response status `200` - added `#/components/schemas/BetaResponseFallbackBlock` to the `content/items/` response property `oneOf` list for the response status `200` - 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 the new optional request property `fallback_credit_token` - added the new optional request property `fallbacks` - added `subschema #2, subschema #3, subschema #6` to the `model` request property `anyOf` list - added `subschema #2, subschema #3, subschema #6` to the `tools/items/oneOf[subschema #20: AdvisorTool_20260301]/model` request property `anyOf` list - added `fallback` discriminator mapping keys to the `messages/items/content/anyOf[subschema #2]/items/` request property - added `#/components/schemas/BetaRequestFallbackBlock` to the `messages/items/content/anyOf[subschema #2]/items/` request property `oneOf` list - added `subschema #2, subschema #3, subschema #6` to the `model` response property `anyOf` list for the response status `200` - added `subschema #2, subschema #3, subschema #6` to the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #3: AdvisorMessageIterationUsage]/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` - removed `subschema #4` from the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #3: AdvisorMessageIterationUsage]/model` response property `anyOf` list for the response status `200` - added `fallback` discriminator mapping keys to the `content/items/` response property for the response status `200` - added `fallback_message` discriminator mapping keys to the `usage/iterations/anyOf[subschema #1]/items/` response property for the response status `200` - added the required property `stop_details/anyOf[subschema #1: RefusalStopDetails]/fallback_credit_token` to the response with the `200` status - added the required property `stop_details/anyOf[subschema #1: RefusalStopDetails]/fallback_has_prefill_claim` to the response with the `200` status - added the required property `stop_details/anyOf[subschema #1: RefusalStopDetails]/recommended_model` to the response with the `200` status - added the required property `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #1: MessageIterationUsage]/model` to the response with the `200` status - **2026-06-06** `546c704d347b` — 2 breaking, 1 warning, 9 info - removed `subschema #13, subschema #14` from the `model` request property `anyOf` list - removed `subschema #13, subschema #14` from the `tools/items/oneOf[subschema #20: AdvisorTool_20260301]/model` request property `anyOf` list - added the new `model_not_found` enum value to the `content/items/oneOf[subschema #8: ResponseAdvisorToolResultBlock]/content/anyOf[subschema #1: ResponseAdvisorToolResultError]/error_code` response property for the response status `200` - added the new optional request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #16: RequestToolSearchToolResultBlock]/content/anyOf[subschema #1: RequestToolSearchToolResultError]/error_message` - added the new optional request property `tools/items/oneOf[subschema #20: AdvisorTool_20260301]/max_tokens` - added `subschema #13, subschema #14` to the `model` request property `anyOf` list - added `subschema #13, subschema #14` to the `tools/items/oneOf[subschema #20: AdvisorTool_20260301]/model` request property `anyOf` list - added the new `model_not_found` enum value to the request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #12: RequestAdvisorToolResultBlock]/content/anyOf[subschema #1: RequestAdvisorToolResultError]/error_code` - added `subschema #13, subschema #14` to the `model` response property `anyOf` list for the response status `200` - added `subschema #13, subschema #14` to the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #3: AdvisorMessageIterationUsage]/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` - removed `subschema #13, subschema #14` from the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #3: AdvisorMessageIterationUsage]/model` response property `anyOf` list for the response status `200` - **2026-05-28** `f9d488f9290d` — 1 warning, 13 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 the new optional request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #12: RequestAdvisorToolResultBlock]/content/anyOf[subschema #2: RequestAdvisorResultBlock]/stop_reason` - added the new optional request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #12: RequestAdvisorToolResultBlock]/content/anyOf[subschema #3: RequestAdvisorRedactedResultBlock]/stop_reason` - added `subschema #2` to the `model` request property `anyOf` list - added `subschema #2` to the `tools/items/oneOf[subschema #20: AdvisorTool_20260301]/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/BetaRequestMidConvSystemBlock` 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 `subschema #2` to the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #3: AdvisorMessageIterationUsage]/model` response property `anyOf` list for the response status `200` - added the required property `content/items/oneOf[subschema #8: ResponseAdvisorToolResultBlock]/content/anyOf[subschema #2: ResponseAdvisorResultBlock]/stop_reason` to the response with the `200` status - added the required property `content/items/oneOf[subschema #8: ResponseAdvisorToolResultBlock]/content/anyOf[subschema #3: ResponseAdvisorRedactedResultBlock]/stop_reason` to the response with the `200` status - added the required property `usage/output_tokens_details` to the response with the `200` status - **2026-05-19** `40e330aba8bc` — 1 info - the request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #20: RequestCompactionBlock]/content` became optional - **2026-05-13** `400ce646c6b2` — 2 info - added the new optional request property `diagnostics` - added the required property `diagnostics` to the response with the `200` status - **2026-04-30** `6edc6519fd32` — 1 info - the `max_tokens` request property's min was decreased from `1.00` to `0.00` - **2026-04-16** `e0696f59ae07` — 2 breaking, 11 info - removed `subschema #13, subschema #14, subschema #15, subschema #16` from the `model` request property `anyOf` list - removed `subschema #13, subschema #14, subschema #15, subschema #16` from the `tools/items/oneOf[subschema #20: AdvisorTool_20260301]/model` request property `anyOf` list - added the new optional request property `messages/items/content/anyOf[subschema #2]/items/oneOf[subschema #20: RequestCompactionBlock]/encrypted_content` - added the new optional request property `output_config/task_budget` - added the new optional request property `user_profile_id` - added `subschema #2, subschema #14, subschema #15, subschema #16, subschema #17` to the `model` request property `anyOf` list - added `subschema #2, subschema #14, subschema #15, subschema #16, subschema #17` to the `tools/items/oneOf[subschema #20: AdvisorTool_20260301]/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` - added `subschema #2, subschema #14, subschema #15, subschema #16, subschema #17` to the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #3: AdvisorMessageIterationUsage]/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` - removed `subschema #13, subschema #14, subschema #15, subschema #16` from the `usage/iterations/anyOf[subschema #1]/items/oneOf[subschema #3: AdvisorMessageIterationUsage]/model` response property `anyOf` list for the response status `200` - added the required property `content/items/oneOf[subschema #16: ResponseCompactionBlock]/encrypted_content` to the response with the `200` status - …earlier changes are on the page: https://skmtc.dev/anthropics/apis/anthropic-api/changes/v1/messages?beta=true/post --- [Operation](https://skmtc.dev/anthropics/apis/anthropic-api/docs/v1/messages?beta=true/post.md) · [API](https://skmtc.dev/anthropics/apis/anthropic-api.md) · [Page](https://skmtc.dev/anthropics/apis/anthropic-api/changes/v1/messages?beta=true/post)