LM Studio Chat API

openapi: 3.1.0
info:
  title: LM Studio Local Server Anthropic Compatibility Chat API
  version: 1.0.0-beta
  description: 'LM Studio runs large language models locally and exposes a local HTTP server with three families of endpoints: the native LM Studio REST API (beta) under `/api/v1`, an OpenAI-compatible surface under `/v1`, and an Anthropic-compatible surface (`/v1/messages`). The server runs on the developer''s own machine (default `http://localhost:1234`). The native `/api/v1` API adds LM Studio-specific capabilities such as MCP via API, stateful chats, model download/load/unload, generation stats (tokens-per-second, time-to-first-token), and optional API-token authentication. Endpoints and paths are transcribed from the public LM Studio developer documentation; request/response bodies follow the documented OpenAI-style message shapes.'
  contact:
    name: LM Studio
    url: https://lmstudio.ai/docs
  license:
    name: Proprietary (LM Studio application)
    url: https://lmstudio.ai/terms
  x-provenance:
    method: generated
    source: https://lmstudio.ai/docs/app/api/endpoints/rest
    generated: '2026-07-20'
servers:
- url: http://localhost:1234
  description: Default local LM Studio server (bind host/port configurable)
tags:
- name: Chat
  description: Native LM Studio chat inference with generation stats.
paths:
  /api/v1/chat:
    post:
      tags:
      - Chat
      operationId: createChat
      summary: Run chat inference (native)
      description: Native LM Studio chat completion. Supports streaming, tool/function calling, structured output via JSON schema, and returns LM Studio generation stats.
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/ChatRequest'
      responses:
        '200':
          description: Chat completion result with generation stats.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ChatResponse'
        '400':
          $ref: '#/components/responses/BadRequest'
        '401':
          $ref: '#/components/responses/Unauthorized'
        '404':
          $ref: '#/components/responses/NotFound'
components:
  schemas:
    ChatRequest:
      type: object
      properties:
        model:
          type: string
          description: Identifier of a loaded model.
        messages:
          type: array
          items:
            $ref: '#/components/schemas/Message'
        stream:
          type: boolean
          default: false
        temperature:
          type: number
        max_tokens:
          type: integer
        tools:
          type: array
          items:
            type: object
        response_format:
          type: object
          description: Structured-output enforcement via JSON schema.
      required:
      - model
      - messages
    Error:
      type: object
      properties:
        error:
          type: object
          properties:
            message:
              type: string
            type:
              type: string
            code:
              type: string
    GenerationStats:
      type: object
      description: LM Studio generation performance metrics.
      properties:
        tokens_per_second:
          type: number
        time_to_first_token:
          type: number
        generation_time:
          type: number
        stop_reason:
          type: string
    ChatResponse:
      type: object
      properties:
        id:
          type: string
        model:
          type: string
        choices:
          type: array
          items:
            type: object
            properties:
              index:
                type: integer
              message:
                $ref: '#/components/schemas/Message'
              finish_reason:
                type: string
        stats:
          $ref: '#/components/schemas/GenerationStats'
        usage:
          type: object
          properties:
            prompt_tokens:
              type: integer
            completion_tokens:
              type: integer
            total_tokens:
              type: integer
    Message:
      type: object
      properties:
        role:
          type: string
          enum:
          - system
          - user
          - assistant
          - tool
        content:
          type: string
      required:
      - role
      - content
  responses:
    NotFound:
      description: The referenced model or resource does not exist.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    Unauthorized:
      description: A required API token was missing or invalid.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    BadRequest:
      description: The request was malformed or referenced an unavailable model.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
  securitySchemes:
    ApiToken:
      type: http
      scheme: bearer
      description: Optional API token. The native `/api/v1` server can be configured to require a bearer token; by default the local server accepts unauthenticated requests from the loopback interface.