> ## Documentation Index > Fetch the complete documentation index at: https://docs.flex.ai/llms.txt > Use this file to discover all available pages before exploring further. # Create a chat completion > Given a list of messages, returns a model-generated response. Supports streaming (SSE), tool use, and (on some models) vision input. **Streaming:** set `stream: true` and `stream_options: { include_usage: true }` to receive token-by-token deltas. The final chunk (the one with `finish_reason` set) carries the `usage` block; you need it for accurate cost tracking. ## OpenAPI ````yaml /inference-api/openapi.yaml post /v1/chat/completions openapi: 3.1.0 info: title: FlexAI Inference API version: 1.0.0 description: | OpenAI-compatible inference API for text, code, reasoning, vision, and embedding models hosted by FlexAI. Use any OpenAI SDK by pointing the `base_url` at this service. contact: name: FlexAI Support email: support@flex.ai url: https://docs.flex.ai/inference-api/overview servers: - url: https://tokens.flex.ai description: Production security: - bearerAuth: [] tags: - name: Chat description: Chat completions (streaming, tool use, vision). - name: Completions description: Legacy text completions. - name: Embeddings description: Generate vector embeddings for text. - name: Models description: Discover available models. - name: Usage description: Programmatic spend and quota for the calling key. paths: /v1/chat/completions: post: tags: - Chat summary: Create a chat completion description: > Given a list of messages, returns a model-generated response. Supports streaming (SSE), tool use, and (on some models) vision input. **Streaming:** set `stream: true` and `stream_options: { include_usage: true }` to receive token-by-token deltas. The final chunk (the one with `finish_reason` set) carries the `usage` block; you need it for accurate cost tracking. operationId: createChatCompletion requestBody: required: true content: application/json: schema: type: object required: - model - messages properties: model: type: string description: Model id. See `GET /v1/models` for available models. example: Meta-Llama-3.1-8B-Instruct-FP8 messages: type: array items: type: object required: - role properties: role: type: string enum: - system - user - assistant - tool content: oneOf: - type: string - type: array items: type: object name: type: string tool_calls: type: array items: type: object tool_call_id: type: string stream: type: boolean default: false stream_options: type: object properties: include_usage: type: boolean description: Required for per-request spend tracking when streaming. temperature: type: number minimum: 0 maximum: 2 default: 1 top_p: type: number minimum: 0 maximum: 1 max_tokens: type: integer minimum: 1 tools: type: array items: type: object required: - type - function properties: type: type: string enum: - function function: type: object required: - name properties: name: type: string description: type: string parameters: type: object tool_choice: oneOf: - type: string enum: - none - auto - required - type: object response_format: type: object properties: type: type: string enum: - text - json_object seed: type: integer stop: oneOf: - type: string - type: array items: type: string user: type: string responses: '200': description: >- Successful response. When `stream: true`, body is an SSE stream of `text/event-stream` chunks. content: application/json: schema: type: object required: - id - object - created - model - choices properties: id: type: string object: type: string enum: - chat.completion created: type: integer model: type: string choices: type: array items: type: object required: - index - message - finish_reason properties: index: type: integer message: type: object properties: role: type: string content: type: - string - 'null' tool_calls: type: array items: type: object finish_reason: type: string enum: - stop - length - tool_calls - content_filter usage: type: object properties: prompt_tokens: type: integer completion_tokens: type: integer total_tokens: type: integer cache_read_input_tokens: type: integer cache_creation_input_tokens: type: integer text/event-stream: schema: type: string description: >- SSE stream. Each event is `data: `. Terminates with `data: [DONE]`. '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '402': $ref: '#/components/responses/PaymentRequired' '404': $ref: '#/components/responses/NotFound' '429': $ref: '#/components/responses/RateLimited' '500': $ref: '#/components/responses/ServerError' components: responses: BadRequest: description: Invalid request — malformed body, unknown model, or schema violation. content: application/json: schema: $ref: '#/components/schemas/Error' Unauthorized: description: Missing or invalid API key. content: application/json: schema: $ref: '#/components/schemas/Error' PaymentRequired: description: Key budget exhausted — add credit in the dashboard to continue. content: application/json: schema: $ref: '#/components/schemas/Error' NotFound: description: Resource not found (e.g., unknown model or job id). content: application/json: schema: $ref: '#/components/schemas/Error' RateLimited: description: | Per-key RPM exceeded. Response includes `Retry-After` and `x-ratelimit-*` headers. headers: Retry-After: schema: type: integer description: Seconds until the next window. x-ratelimit-limit-requests: schema: type: integer x-ratelimit-remaining-requests: schema: type: integer x-ratelimit-reset-requests: schema: type: integer content: application/json: schema: $ref: '#/components/schemas/Error' ServerError: description: Upstream or gateway error. Safe to surface `error.message` to users. content: application/json: schema: $ref: '#/components/schemas/Error' schemas: Error: type: object required: - error properties: error: type: object required: - message - type properties: message: type: string type: type: string example: invalid_request_error code: type: string description: | Stable machine-readable code for the failure. Present on most error paths; OMITTED on FastAPI default-validation bodies. Do not assume always present. doc_url: type: string format: uri description: | FlexAI extension. Link to the relevant dashboard / docs page for the failure mode (e.g. invalid key → /dashboard/keys). Present on auth and quota errors. securitySchemes: bearerAuth: type: http scheme: bearer bearerFormat: sk-xxxx description: | Virtual API key. Create one from the [FlexAI dashboard](https://tokens.flex.ai/dashboard/keys). Pass as `Authorization: Bearer sk-xxxx`. ````