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Messages

Send Message

Sends a new message to an existing chat. Blocks until the model response is complete and returns the message response.

post/chats/{chatId}/messages

Path parameters

chatIdstring required

The unique identifier of the chat.

Request body

messagestring required

The prompt or instruction to send to the model.

systemPromptstring

System-level context for the chat, such as frameworks or development environment details.

mcpServerIdsstring[]

MCP server IDs to enable. When omitted, uses default enabled servers.

Response

A single message in a chat.

idstring required

Unique message identifier.

chatIdstring required

ID of the chat this message belongs to.

role'user' | 'assistant' required

Who produced this message.

createdAtstring date-time required

ISO timestamp when the message was created.

updatedAtstring date-time required

ISO timestamp when the message was last updated.

contentstring required

The trailing prose of the message — the agent’s closing summary, or the user’s message text. Empty string when there is no closing prose.

finishReason'stop' | 'length' | 'content-filter' | 'tool-calls' | 'error' | 'other' nullable required

The reason why message generation finished, including standard completion reasons and error states.

restorableboolean required

True when this is an assistant message that produced restorable code and is not the currently active code.

authorIdstring nullable required

ID of the user who authored a user message; null for assistant messages.

Changes

Changed in 17 of the 34 revisions of this API.4043107

  • 3cf5debd6cf4135See the full diff
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      the attachments/items/ request property type/format changed from object/ to / (media type: application/json)

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      removed the request property attachments/items/url (media type: application/json)

      request-property-removed

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      removed the request property attachments/items/url (media type: application/x-www-form-urlencoded)

      request-property-removed

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      removed the request property attachments/items/url (media type: multipart/form-data)

      request-property-removed

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      added subschema #1 subschema #2 to the attachments/items/ request property anyOf list (media type: application/json)

      request-property-any-of-added

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      added subschema #1 subschema #2 to the attachments/items/ request property anyOf list (media type: application/x-www-form-urlencoded)

      request-property-any-of-added

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      added subschema #1 subschema #2 to the attachments/items/ request property anyOf list (media type: multipart/form-data)

      request-property-any-of-added

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      the attachments/items/ request property type/format was generalized from object/ to / (media type: application/x-www-form-urlencoded)

      request-property-type-generalized

    • ○

      the attachments/items/ request property type/format was generalized from object/ to / (media type: multipart/form-data)

      request-property-type-generalized

  • 76c7f743f0e92See the full diff
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      added the optional property parts/items/oneOf[subschema #7]/suggestedPermissions/items/toolDisplayName to the response with the 200 status

      response-optional-property-added

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      added the optional property parts/items/oneOf[subschema #7]/toolDisplayName to the response with the 200 status

      response-optional-property-added

  • ca413e5ca7101See the full diff
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      added subschema #4 to the parts/items/oneOf[subschema #8]/data response property anyOf list for the response status 200

      response-property-any-of-added

  • da68370a2aea211329See the full diff
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      for the path request parameter chatId, the minLength was increased from 0 to 1

      request-parameter-min-length-increased

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      removed subschema #1 subschema #2 subschema #3 from the skills/items/ request property anyOf list

      request-property-any-of-removed

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      removed the enum value v0-auto of the request property modelConfiguration/modelId

      request-property-enum-value-removed

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      the message request property's minLength was increased from 0 to 1

      request-property-min-length-increased

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      response property authorId list-of-types was widened by adding types null to media type application/json of response 200

      response-property-list-of-types-widened

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      removed the required property apiUrl from the response with the 200 status

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      removed the required property error from the response with the 401 status

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      removed the required property error from the response with the 403 status

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      removed the required property error from the response with the 404 status

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      removed the required property error from the response with the 422 status

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      removed the required property error from the response with the 500 status

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      removed the required property favorite from the response with the 200 status

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      removed the required property messages from the response with the 200 status

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      removed the required property metadata from the response with the 200 status

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      removed the required property object from the response with the 200 status

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      removed the required property permissions from the response with the 200 status

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      removed the required property privacy from the response with the 200 status

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      removed the required property shareable from the response with the 200 status

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      removed the required property text from the response with the 200 status

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      removed the required property url from the response with the 200 status

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      removed the required property webUrl from the response with the 200 status

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      removed the request property action

      request-property-removed

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      removed the request property attachedSkillIds

      request-property-removed

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      removed the request property modelConfiguration/thinking

      request-property-removed

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      removed the request property responseMode

      request-property-removed

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      removed the request property system

      request-property-removed

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      removed the optional property demo from the response with the 200 status

      response-optional-property-removed

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      removed the optional property files from the response with the 200 status

      response-optional-property-removed

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      removed the optional property latestVersion from the response with the 200 status

      response-optional-property-removed

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      removed the optional property modelConfiguration from the response with the 200 status

      response-optional-property-removed

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      removed the optional property name from the response with the 200 status

      response-optional-property-removed

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      removed the optional property projectId from the response with the 200 status

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      removed the optional property title from the response with the 200 status

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      removed the optional property vercelProjectId from the response with the 200 status

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    • ○

      api operation id chats.sendMessage removed and replaced with messages.send

      api-operation-id-removed

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      the endpoint scheme security apiKey was removed from the API

      api-security-removed

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      api tag Messages added

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      api tag chats removed

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      added the new optional request property systemPrompt

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      added the media type application/x-www-form-urlencoded to the request body

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      added the media type multipart/form-data to the request body

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      the request property modelConfiguration/imageGenerations with a default value became required

      request-property-became-required-with-default

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      the request property modelConfiguration/modelId with a default value became required

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      the attachments request property default value was removed

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      added subschema #1 subschema #2 subschema #3 to the skills/items/ request property oneOf list

      request-property-one-of-added

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      removed the non-success response with the status 409

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      removed the non-success response with the status 413

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      removed the non-success response with the status 429

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      added the optional property attachments to the response with the 200 status

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      the response property updatedAt became required for the status 200

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      the updatedAt response's property pattern ^(?:(?:\d\d[2468][048]|\d\d[13579][26]|\d\d0[48]|[02468][048]00|[13579][26]00)-02-29|\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\d|30)|(?:02)-(?:0[1-9]|1\d|2[0-8])))T(?:(?:[01]\d|2[0-3]):[0-5]\d(?::[0-5]\d(?:\.\d+)?)?(?:Z))$ was added for the status 200

      response-property-pattern-added

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      added the required property chatId to the response with the 200 status

      response-required-property-added

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      added the required property content to the response with the 200 status

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      added the required property finishReason to the response with the 200 status

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      added the required property message to the response with the 401 status

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      added the required property message to the response with the 403 status

      response-required-property-added

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      added the required property message to the response with the 404 status

      response-required-property-added

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      added the required property message to the response with the 422 status

      response-required-property-added

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      added the required property message to the response with the 500 status

      response-required-property-added

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      added the required property parts to the response with the 200 status

      response-required-property-added

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      added the required property restorable to the response with the 200 status

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      added the required property role to the response with the 200 status

      response-required-property-added

    • ○

      added the required property usage to the response with the 200 status

      response-required-property-added

    This revision also has 50 changes that name no endpoint, such as unreferenced schemas being removed. See the revision's changelog

  • b5392124577911See the full diff
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      added the new v0-opus-4.7-fast enum value to the modelConfiguration/modelId response property for the response status 200

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      added the new optional request property skills

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  • 670c302548ec15See the full diff
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      added the new v0-opus-4.7 enum value to the modelConfiguration/modelId response property for the response status 200

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      added the new optional request property action

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      added the new optional request property attachedSkillIds

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      request property modelConfiguration/modelId reactivated

      request-property-reactivated

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      added the optional property vercelProjectId to the response with the 200 status

      response-optional-property-added

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      response property modelConfiguration/modelId reactivated

      response-property-reactivated

  • b73ab7a6f3171See the full diff
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      added the new optional request property mcpServerIds

      new-optional-request-property

  • 79811cd54faa22See the full diff
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      added the new design-mode enum value to the messages/items/type response property for the response status 200

      response-property-enum-value-added

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      added the new v0-auto enum value to the modelConfiguration/modelId response property for the response status 200

      response-property-enum-value-added

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      added the new v0-auto enum value to the request property modelConfiguration/modelId

      request-property-enum-value-added

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      added the required property metadata to the response with the 200 status

      response-required-property-added

  • 8b21bf5afcfa32See the full diff
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      added the new cloned-repo enum value to the messages/items/type response property for the response status 200

      response-property-enum-value-added

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      added the new manual-commit enum value to the messages/items/type response property for the response status 200

      response-property-enum-value-added

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      added the new v0-max-fast enum value to the modelConfiguration/modelId response property for the response status 200

      response-property-enum-value-added

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      added the new v0-max-fast enum value to the request property modelConfiguration/modelId

      request-property-enum-value-added

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      removed the unknown enum value from the messages/items/finishReason response property for the response status 200

      response-property-enum-value-removed

  • 86302d0793b16614See the full diff
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      removed the enum value v0-1.5-lg of the request property modelConfiguration/modelId

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      removed the enum value v0-1.5-md of the request property modelConfiguration/modelId

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      removed the enum value v0-1.5-sm of the request property modelConfiguration/modelId

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      removed the enum value v0-gpt-5 of the request property modelConfiguration/modelId

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      removed the enum value v0-opus-4.5 of the request property modelConfiguration/modelId

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      removed the required property messages/items/experimental_content/items/anyOf[subschema #2]/prefixItems[subschema #2]/~standard from the response with the 200 status

      response-required-property-removed

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      added the new answered-questions enum value to the messages/items/type response property for the response status 200

      response-property-enum-value-added

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      added the new fix-cve enum value to the messages/items/type response property for the response status 200

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      added the new pull-changes enum value to the messages/items/type response property for the response status 200

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      added the new v0-max enum value to the modelConfiguration/modelId response property for the response status 200

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      added the new v0-mini enum value to the modelConfiguration/modelId response property for the response status 200

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      added the new v0-pro enum value to the modelConfiguration/modelId response property for the response status 200

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      the modelId request property default value changed from v0-1.5-md to v0-pro

      request-property-default-value-changed

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      added the new v0-max enum value to the request property modelConfiguration/modelId

      request-property-enum-value-added

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      added the new v0-mini enum value to the request property modelConfiguration/modelId

      request-property-enum-value-added

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      added the new v0-pro enum value to the request property modelConfiguration/modelId

      request-property-enum-value-added

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      the modelId response's property default value changed from v0-1.5-md to v0-pro for the status 200

      response-property-default-value-changed

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      removed the v0-1.5-lg enum value from the modelConfiguration/modelId response property for the response status 200

      response-property-enum-value-removed

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      removed the v0-1.5-md enum value from the modelConfiguration/modelId response property for the response status 200

      response-property-enum-value-removed

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      removed the v0-1.5-sm enum value from the modelConfiguration/modelId response property for the response status 200

      response-property-enum-value-removed

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      removed the v0-gpt-5 enum value from the modelConfiguration/modelId response property for the response status 200

      response-property-enum-value-removed

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      removed the v0-opus-4.5 enum value from the modelConfiguration/modelId response property for the response status 200

      response-property-enum-value-removed

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      added the required property messages/items/experimental_content/items/anyOf[subschema #2]/prefixItems[subschema #2]/apply to the response with the 200 status

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      added the required property messages/items/experimental_content/items/anyOf[subschema #2]/prefixItems[subschema #2]/exactOptional to the response with the 200 status

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      added the required property messages/items/experimental_content/items/anyOf[subschema #2]/prefixItems[subschema #2]/toJSONSchema to the response with the 200 status

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      added the required property messages/items/experimental_content/items/anyOf[subschema #2]/prefixItems[subschema #2]/with to the response with the 200 status

      response-required-property-added