Martian Gateway Chat Completions Streaming (HTTP + SSE)

asyncapi: '2.6.0'
id: 'urn:com:withmartian:gateway:v1:chat-completions:sse'
info:
  title: Martian Gateway Chat Completions Streaming (HTTP + SSE)
  version: '1.0.0'
  description: |
    AsyncAPI 2.6 description of the Martian Gateway's **chat completion
    streaming** surface.

    Martian does not publish a WebSocket API. The Martian Gateway is an
    OpenAI-compatible model router; its only asynchronous / event-style
    transport is **HTTP Server-Sent Events (SSE)** delivered over the same
    REST endpoint (`POST /v1/chat/completions`) when the request body sets
    `stream: true`. SSE is a one-way, server-to-client HTTP streaming
    channel; it is **not** WebSocket.

    Because Martian mirrors the OpenAI Chat Completions streaming contract,
    tokens are sent as data-only server-sent events as they become available,
    with the stream terminated by a `data: [DONE]` message.

    This AsyncAPI document models only the streamed events emitted by the
    Gateway's SSE response. The request body itself (model in
    provider/model-name format, messages, etc.) is modeled in the companion
    OpenAPI document at `openapi/martian-ai-openapi.yml`.
  contact:
    name: API Evangelist
    email: kin@apievangelist.com
    url: https://apievangelist.com
  license:
    name: API documentation - Martian Terms of Service
    url: https://www.withmartian.com
  x-transport-notes:
    transport: HTTP Server-Sent Events (SSE)
    protocol: https
    direction: server-to-client (one-way)
    mediaType: text/event-stream
    triggeredBy: 'POST https://api.withmartian.com/v1/chat/completions with request body { "stream": true }'
servers:
  production:
    url: api.withmartian.com
    protocol: https
    description: >-
      Martian Gateway. The streaming response is delivered as HTTP
      Server-Sent Events over this host when stream=true. This is not a
      WebSocket server.
channels:
  /v1/chat/completions:
    description: >-
      SSE stream of chat completion chunks returned by POST /v1/chat/completions
      when the request body sets stream=true.
    bindings:
      http:
        type: request
        method: POST
    subscribe:
      operationId: receiveChatCompletionChunks
      summary: Receive streamed chat completion chunks as Server-Sent Events.
      bindings:
        http:
          type: response
      message:
        $ref: '#/components/messages/ChatCompletionChunk'
components:
  messages:
    ChatCompletionChunk:
      name: ChatCompletionChunk
      title: Chat Completion Chunk (SSE data event)
      contentType: text/event-stream
      summary: >-
        A single data-only Server-Sent Event carrying an incremental chat
        completion delta. The terminal event is the literal string [DONE].
      payload:
        $ref: '#/components/schemas/ChatCompletionChunk'
  schemas:
    ChatCompletionChunk:
      type: object
      properties:
        id:
          type: string
        object:
          type: string
          example: chat.completion.chunk
        created:
          type: integer
        model:
          type: string
          description: The provider/model-name the router selected to serve the request.
        choices:
          type: array
          items:
            type: object
            properties:
              index:
                type: integer
              delta:
                type: object
                properties:
                  role:
                    type: string
                  content:
                    type: string
              finish_reason:
                type: string
                nullable: true