Martian Chat Completions API

openapi: 3.0.1
info:
  title: Martian Gateway Chat Completions 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: Chat Completions
paths:
  /v1/chat/completions:
    post:
      operationId: createChatCompletion
      tags:
      - Chat Completions
      summary: Create a routed chat completion
      description: OpenAI-compatible chat completions endpoint. Supports most parameters of the OpenAI Chat Completions API. The model is specified as a provider/model-name string, and Martian routes the request to the best underlying model.
      security:
      - bearerAuth: []
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/ChatCompletionRequest'
      responses:
        '200':
          description: A chat completion response, or a stream of Server-Sent Events when stream is true.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ChatCompletionResponse'
            text/event-stream:
              schema:
                type: string
                description: Server-Sent Events stream of partial chat completion chunks when stream is true.
        '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.
    ChatCompletionRequest:
      type: object
      required:
      - model
      - messages
      properties:
        model:
          type: string
          description: Routing target in provider/model-name format (for example, openai/gpt-4.1-nano).
          example: openai/gpt-4.1-nano
        messages:
          type: array
          description: A list of messages comprising the conversation so far.
          items:
            $ref: '#/components/schemas/ChatMessage'
        max_tokens:
          type: integer
          description: The maximum number of tokens to generate in the completion.
        temperature:
          type: number
          description: Sampling temperature.
        top_p:
          type: number
          description: Nucleus sampling probability mass.
        stream:
          type: boolean
          description: If true, partial deltas are sent as Server-Sent Events.
          default: false
        stop:
          type: array
          items:
            type: string
          description: Up to a few sequences where the API will stop generating further tokens.
    ChatCompletionResponse:
      type: object
      properties:
        id:
          type: string
        object:
          type: string
          example: chat.completion
        created:
          type: integer
        model:
          type: string
          description: The provider/model-name that the router selected to serve the request.
        choices:
          type: array
          items:
            type: object
            properties:
              index:
                type: integer
              message:
                $ref: '#/components/schemas/ChatMessage'
              finish_reason:
                type: string
        usage:
          $ref: '#/components/schemas/Usage'
    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.