> ## Documentation Index > Fetch the complete documentation index at: https://docs.megallm.io/llms.txt > Use this file to discover all available pages before exploring further. # Create chat completion > Generate conversational AI responses using the OpenAI-compatible chat completions API ## OpenAPI ````yaml /cn/api-reference/openapi.json post /chat/completions openapi: 3.1.0 info: title: MegaLLM API description: >- Unified API for accessing 70+ AI models through OpenAI-compatible and Anthropic-compatible endpoints version: 1.0.0 contact: name: MegaLLM Support email: hi@megallm.io url: https://megallm.io license: name: Proprietary url: https://megallm.io/terms-of-service servers: - url: https://ai.megallm.io/v1 description: Production API Server security: - bearerAuth: [] - apiKeyAuth: [] tags: - name: Chat description: OpenAI-compatible chat completions API - name: Messages description: Anthropic-compatible messages API - name: Models description: List available AI models - name: Authentication description: API authentication endpoints paths: /chat/completions: post: tags: - Chat summary: Create chat completion description: >- Generate conversational AI responses using the OpenAI-compatible chat completions API operationId: createChatCompletion requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/ChatCompletionRequest' examples: basic: summary: Basic chat completion value: model: gpt-4 messages: - role: system content: You are a helpful assistant. - role: user content: What is the capital of France? streaming: summary: Streaming chat completion value: model: gpt-4 messages: - role: user content: Tell me a story stream: true function_calling: summary: Function calling value: model: gpt-4 messages: - role: user content: What's the weather in London? tools: - type: function function: name: get_weather description: Get current weather parameters: type: object properties: location: type: string required: - location responses: '200': description: Successful response content: application/json: schema: $ref: '#/components/schemas/ChatCompletionResponse' text/event-stream: schema: type: string description: Server-sent events stream (when stream=true) '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '429': $ref: '#/components/responses/RateLimit' '500': $ref: '#/components/responses/ServerError' security: - bearerAuth: [] components: schemas: ChatCompletionRequest: type: object required: - model - messages properties: model: type: string description: Model ID (e.g., gpt-4, claude-3.5-sonnet) example: gpt-4 messages: type: array description: Array of message objects items: $ref: '#/components/schemas/ChatMessage' temperature: type: number minimum: 0 maximum: 2 default: 0.7 description: Sampling temperature (0.0 - 2.0) max_tokens: type: integer description: Maximum tokens to generate stream: type: boolean default: false description: Enable streaming responses tools: type: array description: Available functions/tools items: $ref: '#/components/schemas/Tool' tool_choice: oneOf: - type: string enum: - auto - required - none - type: object description: Controls tool calling behavior top_p: type: number minimum: 0 maximum: 1 description: Nucleus sampling parameter frequency_penalty: type: number minimum: -2 maximum: 2 default: 0 description: Penalize frequent tokens presence_penalty: type: number minimum: -2 maximum: 2 default: 0 description: Penalize repeated tokens 'n': type: integer default: 1 description: Number of completions to generate stop: oneOf: - type: string - type: array items: type: string description: Stop sequences user: type: string description: Unique user identifier ChatCompletionResponse: type: object properties: id: type: string example: chatcmpl-abc123 object: type: string enum: - chat.completion created: type: integer description: Unix timestamp model: type: string example: gpt-4 choices: type: array items: type: object properties: index: type: integer message: $ref: '#/components/schemas/ChatMessage' finish_reason: type: string enum: - stop - length - tool_calls - content_filter usage: $ref: '#/components/schemas/Usage' ChatMessage: type: object required: - role - content properties: role: type: string enum: - system - user - assistant - tool description: Message role content: oneOf: - type: string - type: array items: type: object description: Message content (text or multi-part) name: type: string description: Participant name tool_calls: type: array description: Tool calls made by assistant items: $ref: '#/components/schemas/ToolCall' tool_call_id: type: string description: ID of tool call (for tool role) Tool: type: object required: - type - function properties: type: type: string enum: - function description: Tool type function: type: object required: - name - parameters properties: name: type: string description: Function name description: type: string description: Function description parameters: type: object description: JSON Schema for parameters Usage: type: object properties: prompt_tokens: type: integer completion_tokens: type: integer total_tokens: type: integer Error: type: object properties: error: type: object properties: message: type: string type: type: string code: type: string ToolCall: type: object properties: id: type: string description: Tool call ID type: type: string enum: - function function: type: object properties: name: type: string arguments: type: string description: JSON string of arguments responses: BadRequest: description: Bad request - Invalid parameters content: application/json: schema: $ref: '#/components/schemas/Error' example: error: message: Invalid request parameters type: invalid_request_error code: invalid_parameters Unauthorized: description: Unauthorized - Invalid or missing API key content: application/json: schema: $ref: '#/components/schemas/Error' example: error: message: Invalid authentication credentials type: invalid_request_error code: invalid_api_key RateLimit: description: Rate limit exceeded content: application/json: schema: $ref: '#/components/schemas/Error' example: error: message: Rate limit exceeded. Please retry after some time. type: rate_limit_error code: rate_limit_exceeded ServerError: description: Internal server error content: application/json: schema: $ref: '#/components/schemas/Error' example: error: message: Internal server error type: api_error code: internal_error securitySchemes: bearerAuth: type: http scheme: bearer bearerFormat: API Key description: Bearer token authentication (OpenAI-compatible) apiKeyAuth: type: apiKey in: header name: x-api-key description: API key authentication (Anthropic-compatible) ````