Anthropic Claude Messages API

openapi: 3.1.0
info:
  title: Anthropic Claude 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
tags:
  - name: Messages
    description: Create messages with Claude models.
  - name: Models
    description: List and inspect available Claude models.
  - name: Token Counting
    description: Count tokens for a prospective Messages request.
  - name: Message Batches
    description: Submit and manage asynchronous Message Batches.
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'
  /v1/messages/count_tokens:
    post:
      tags:
        - Token Counting
      summary: Count tokens for a Messages request
      description: Count the number of input tokens that a Messages request would consume, without actually creating a Message.
      operationId: countMessageTokens
      parameters:
        - $ref: '#/components/parameters/AnthropicVersion'
        - $ref: '#/components/parameters/AnthropicBeta'
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CountTokensRequest'
      responses:
        '200':
          description: Token count response.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/CountTokensResponse'
        '400':
          $ref: '#/components/responses/ErrorResponse'
  /v1/messages/batches:
    get:
      tags:
        - Message Batches
      summary: List Message Batches
      description: List Message Batches in the workspace.
      operationId: listMessageBatches
      parameters:
        - $ref: '#/components/parameters/AnthropicVersion'
        - name: before_id
          in: query
          schema:
            type: string
        - name: after_id
          in: query
          schema:
            type: string
        - name: limit
          in: query
          schema:
            type: integer
            minimum: 1
            maximum: 100
            default: 20
      responses:
        '200':
          description: A page of Message Batch objects.
    post:
      tags:
        - Message Batches
      summary: Create a Message Batch
      description: Submit a batch of Messages requests for asynchronous processing.
      operationId: createMessageBatch
      parameters:
        - $ref: '#/components/parameters/AnthropicVersion'
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              required: [requests]
              properties:
                requests:
                  type: array
                  items:
                    type: object
                    required: [custom_id, params]
                    properties:
                      custom_id:
                        type: string
                      params:
                        $ref: '#/components/schemas/CreateMessageRequest'
      responses:
        '200':
          description: The created Message Batch object.
  /v1/messages/batches/{message_batch_id}:
    get:
      tags:
        - Message Batches
      summary: Retrieve a Message Batch
      operationId: getMessageBatch
      parameters:
        - $ref: '#/components/parameters/AnthropicVersion'
        - name: message_batch_id
          in: path
          required: true
          schema:
            type: string
      responses:
        '200':
          description: A Message Batch object.
  /v1/messages/batches/{message_batch_id}/cancel:
    post:
      tags:
        - Message Batches
      summary: Cancel a Message Batch
      operationId: cancelMessageBatch
      parameters:
        - $ref: '#/components/parameters/AnthropicVersion'
        - name: message_batch_id
          in: path
          required: true
          schema:
            type: string
      responses:
        '200':
          description: The Message Batch object with updated status.
  /v1/messages/batches/{message_batch_id}/results:
    get:
      tags:
        - Message Batches
      summary: Retrieve Message Batch results
      description: Stream the JSONL results of an ended Message Batch.
      operationId: getMessageBatchResults
      parameters:
        - $ref: '#/components/parameters/AnthropicVersion'
        - name: message_batch_id
          in: path
          required: true
          schema:
            type: string
      responses:
        '200':
          description: A stream of JSONL results, one per batched request.
          content:
            application/x-jsonlines:
              schema:
                type: string
  /v1/models:
    get:
      tags:
        - Models
      summary: List available models
      operationId: listModels
      parameters:
        - $ref: '#/components/parameters/AnthropicVersion'
        - name: before_id
          in: query
          schema:
            type: string
        - name: after_id
          in: query
          schema:
            type: string
        - name: limit
          in: query
          schema:
            type: integer
            minimum: 1
            maximum: 1000
            default: 20
      responses:
        '200':
          description: A page of Model objects.
  /v1/models/{model_id}:
    get:
      tags:
        - Models
      summary: Get a model
      operationId: getModel
      parameters:
        - $ref: '#/components/parameters/AnthropicVersion'
        - name: model_id
          in: path
          required: true
          schema:
            type: string
      responses:
        '200':
          description: A Model object.
components:
  securitySchemes:
    ApiKeyAuth:
      type: apiKey
      in: header
      name: x-api-key
      description: Anthropic API key. Send as the `x-api-key` header on every request.
  parameters:
    AnthropicVersion:
      name: anthropic-version
      in: header
      required: true
      description: API version, e.g. `2023-06-01`.
      schema:
        type: string
        default: "2023-06-01"
    AnthropicBeta:
      name: anthropic-beta
      in: header
      required: false
      description: Optional comma-separated list of beta feature flags.
      schema:
        type: string
  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
    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'
    Usage:
      type: object
      properties:
        input_tokens:
          type: integer
        output_tokens:
          type: integer
        cache_creation_input_tokens:
          type: integer
        cache_read_input_tokens:
          type: integer
    CountTokensRequest:
      type: object
      required: [model, messages]
      properties:
        model:
          type: string
        messages:
          type: array
          items:
            $ref: '#/components/schemas/InputMessage'
        system:
          oneOf:
            - type: string
            - type: array
              items:
                type: object
        tools:
          type: array
          items:
            $ref: '#/components/schemas/Tool'
    CountTokensResponse:
      type: object
      properties:
        input_tokens:
          type: integer
        cache_creation_input_tokens:
          type: integer
        cache_read_input_tokens:
          type: integer
    Error:
      type: object
      properties:
        type:
          type: string
        error:
          type: object
          properties:
            type:
              type: string
            message:
              type: string
  responses:
    ErrorResponse:
      description: An error response.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
security:
  - ApiKeyAuth: []