Open WebUI Anthropic API

openapi: 3.1.0
info:
  title: Open WebUI Anthropic API
  description: 'REST API exposed by a self-hosted Open WebUI instance. Endpoints include an

    OpenAI-compatible chat completions surface, an Anthropic-compatible messages

    endpoint, and a passthrough proxy for native Ollama endpoints. Authentication

    uses a Bearer token (Open WebUI session token or a per-user API key); each

    API key inherits the permissions of the user who created it.

    '
  version: 1.0.0
  contact:
    name: Open WebUI Documentation
    url: https://docs.openwebui.com/
servers:
- url: http://localhost:3000
  description: Default local Open WebUI deployment
- url: https://{host}
  description: User-deployed Open WebUI instance
  variables:
    host:
      default: openwebui.example.com
security:
- BearerAuth: []
tags:
- name: Anthropic
paths:
  /api/v1/messages:
    post:
      tags:
      - Anthropic
      summary: Anthropic-compatible messages
      description: Compatible with the Anthropic Messages API surface; usable with the Anthropic SDK and Claude Code.
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              additionalProperties: true
              properties:
                model:
                  type: string
                max_tokens:
                  type: integer
                messages:
                  type: array
                  items:
                    $ref: '#/components/schemas/Message'
      responses:
        '200':
          description: Anthropic-compatible messages response.
          content:
            application/json:
              schema:
                type: object
                additionalProperties: true
components:
  schemas:
    Message:
      type: object
      properties:
        role:
          type: string
          enum:
          - system
          - user
          - assistant
          - tool
        content:
          type: string
      required:
      - role
      - content
  securitySchemes:
    BearerAuth:
      type: http
      scheme: bearer
      description: 'Bearer token: Open WebUI session token or per-user API key. Each API key

        inherits the permissions of the user who created it.

        '