openapi: 3.0.1
info:
  title: Martian Gateway Chat Completions Messages API
  description: OpenAPI specification for the Martian Gateway, an LLM model router. The Gateway exposes an OpenAI-compatible chat completions endpoint, an Anthropic Messages-compatible endpoint, and a models listing endpoint. Requests are routed dynamically across a catalog of provider models. Models are addressed with a provider/model-name string (for example, openai/gpt-4.1-nano).
  termsOfService: https://www.withmartian.com
  contact:
    name: Martian
    url: https://www.withmartian.com
  version: '1.0'
servers:
- url: https://api.withmartian.com
  description: Martian Gateway production server
tags:
- name: Messages
paths:
  /v1/messages:
    post:
      operationId: createMessage
      tags:
      - Messages
      summary: Create a routed message (Anthropic-compatible)
      description: Anthropic Messages-compatible endpoint. Supports most parameters of the Anthropic Messages API and routes the request through the Martian Gateway. The model is specified as a provider/model-name string.
      security:
      - bearerAuth: []
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/MessagesRequest'
      responses:
        '200':
          description: An Anthropic-compatible message response.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/MessagesResponse'
        '401':
          description: Authentication failed (missing or invalid API key).
        '429':
          description: Rate limit or quota exceeded.
components:
  schemas:
    ChatMessage:
      type: object
      required:
      - role
      - content
      properties:
        role:
          type: string
          enum:
          - system
          - user
          - assistant
          - tool
          description: The role of the author of this message.
        content:
          type: string
          description: The contents of the message.
        name:
          type: string
          description: An optional name for the participant.
    MessagesResponse:
      type: object
      properties:
        id:
          type: string
        type:
          type: string
          example: message
        role:
          type: string
          example: assistant
        model:
          type: string
          description: The provider/model-name that the router selected.
        content:
          type: array
          items:
            type: object
            properties:
              type:
                type: string
              text:
                type: string
        usage:
          $ref: '#/components/schemas/Usage'
    MessagesRequest:
      type: object
      required:
      - model
      - messages
      - max_tokens
      properties:
        model:
          type: string
          description: Routing target in provider/model-name format.
          example: anthropic/claude-sonnet-4
        messages:
          type: array
          description: Anthropic-style input messages.
          items:
            $ref: '#/components/schemas/ChatMessage'
        max_tokens:
          type: integer
          description: The maximum number of tokens to generate.
        system:
          type: string
          description: An optional system prompt.
        temperature:
          type: number
          description: Sampling temperature.
        stream:
          type: boolean
          default: false
    Usage:
      type: object
      properties:
        prompt_tokens:
          type: integer
        completion_tokens:
          type: integer
        total_tokens:
          type: integer
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      description: Provide your Martian API key as a Bearer token in the Authorization header.