Anthropic Claude Messages API

openapi: 3.1.0
info:
  title: Anthropic Claude Message Batches Messages API
  version: '2023-06-01'
  description: 'REST API for sending messages to Claude models with support for streaming,

    tool use, vision, system prompts, prompt caching, and extended thinking.

    Authentication uses an x-api-key header along with an anthropic-version header.

    '
  contact:
    name: Anthropic Support
    url: https://support.anthropic.com
  license:
    name: Anthropic Commercial Terms of Service
    url: https://www.anthropic.com/legal/commercial-terms
servers:
- url: https://api.anthropic.com
  description: Anthropic API production
security:
- ApiKeyAuth: []
tags:
- name: Messages
  description: Create messages with Claude models.
paths:
  /v1/messages:
    post:
      tags:
      - Messages
      summary: Create a Message
      description: Send a structured list of input messages with text and/or image content, and the model will generate the next message in the conversation.
      operationId: createMessage
      parameters:
      - $ref: '#/components/parameters/AnthropicVersion'
      - $ref: '#/components/parameters/AnthropicBeta'
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateMessageRequest'
      responses:
        '200':
          description: 'A Message object (or a stream of server-sent events if `stream: true`).'
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Message'
            text/event-stream:
              schema:
                type: string
                description: Stream of message events when `stream` is true.
        '400':
          $ref: '#/components/responses/ErrorResponse'
        '401':
          $ref: '#/components/responses/ErrorResponse'
        '429':
          $ref: '#/components/responses/ErrorResponse'
components:
  schemas:
    CreateMessageRequest:
      type: object
      required:
      - model
      - max_tokens
      - messages
      properties:
        model:
          type: string
          description: Model identifier, e.g. `claude-opus-4-5`, `claude-sonnet-4-5`, `claude-haiku-4-5`.
        max_tokens:
          type: integer
          minimum: 1
          description: Maximum number of tokens to generate before stopping.
        messages:
          type: array
          items:
            $ref: '#/components/schemas/InputMessage'
        system:
          oneOf:
          - type: string
          - type: array
            items:
              type: object
        temperature:
          type: number
          minimum: 0
          maximum: 1
        top_p:
          type: number
        top_k:
          type: integer
        stop_sequences:
          type: array
          items:
            type: string
        stream:
          type: boolean
          default: false
        tools:
          type: array
          items:
            $ref: '#/components/schemas/Tool'
        tool_choice:
          type: object
        thinking:
          type: object
          properties:
            type:
              type: string
              enum:
              - enabled
              - disabled
            budget_tokens:
              type: integer
        service_tier:
          type: string
          enum:
          - auto
          - standard_only
        metadata:
          type: object
          properties:
            user_id:
              type: string
    InputMessage:
      type: object
      required:
      - role
      - content
      properties:
        role:
          type: string
          enum:
          - user
          - assistant
        content:
          oneOf:
          - type: string
          - type: array
            items:
              type: object
    Tool:
      type: object
      required:
      - name
      - input_schema
      properties:
        name:
          type: string
        description:
          type: string
        input_schema:
          type: object
    Usage:
      type: object
      properties:
        input_tokens:
          type: integer
        output_tokens:
          type: integer
        cache_creation_input_tokens:
          type: integer
        cache_read_input_tokens:
          type: integer
    Message:
      type: object
      properties:
        id:
          type: string
        type:
          type: string
          enum:
          - message
        role:
          type: string
          enum:
          - assistant
        model:
          type: string
        content:
          type: array
          items:
            type: object
        stop_reason:
          type: string
          enum:
          - end_turn
          - max_tokens
          - stop_sequence
          - tool_use
          - pause_turn
          - refusal
        stop_sequence:
          type: string
          nullable: true
        usage:
          $ref: '#/components/schemas/Usage'
    Error:
      type: object
      properties:
        type:
          type: string
        error:
          type: object
          properties:
            type:
              type: string
            message:
              type: string
  parameters:
    AnthropicBeta:
      name: anthropic-beta
      in: header
      required: false
      description: Optional comma-separated list of beta feature flags.
      schema:
        type: string
    AnthropicVersion:
      name: anthropic-version
      in: header
      required: true
      description: API version, e.g. `2023-06-01`.
      schema:
        type: string
        default: '2023-06-01'
  responses:
    ErrorResponse:
      description: An error response.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
  securitySchemes:
    ApiKeyAuth:
      type: apiKey
      in: header
      name: x-api-key
      description: Anthropic API key. Send as the `x-api-key` header on every request.