> ## Documentation Index > Fetch the complete documentation index at: https://impossibl.com/docs/llms.txt > Use this file to discover all available pages before exploring further. # Create a chat completion (OpenAI-compatible) > Drop-in compatible with OpenAI's Chat Completions API. Set `stream: true` for SSE. ## OpenAPI ````yaml /openapi.yaml post /v1/chat/completions openapi: 3.1.0 info: title: Impossibl AI API version: 0.0.1 description: > The Impossibl AI API is one API for all AI providers, OpenAI-compatible across OpenAI, Anthropic, Google, xAI, and more (`GET /v1/models` lists the full catalog), billed from a prepaid credit balance. Provider usage is billed at provider list prices with no usage markup. Prepaid credit purchases charge a separate fixed 5% platform fee before tax. **Agent quickstart** 1. `POST /v1/accounts` — create a funded account; you get an API key and a signup-bonus balance in one call (no human step required). 2. Call `POST /v1/chat/completions`, `POST /v1/responses`, or `POST /v1/audio/transcriptions` with `Authorization: Bearer ` and a `provider/model` id from `GET /v1/models`. 3. Credits are deducted per request by token or audio-duration usage; check `GET /v1/account`. servers: - url: https://api.impossibl.com description: Production - url: http://localhost:8787 description: Local dev security: - BearerKey: [] paths: /v1/chat/completions: post: summary: Create a chat completion (OpenAI-compatible) description: >- Drop-in compatible with OpenAI's Chat Completions API. Set `stream: true` for SSE. operationId: createChatCompletion requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/ChatCompletionRequest' responses: '200': description: > A `chat.completion` object. When `stream: true`, the body is instead an SSE stream of `chat.completion.chunk` objects terminated by `data: [DONE]`. content: application/json: schema: $ref: '#/components/schemas/ChatCompletion' text/event-stream: schema: $ref: '#/components/schemas/ChatCompletionChunk' '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '402': $ref: '#/components/responses/InsufficientCredits' '404': $ref: '#/components/responses/UnknownModel' '502': $ref: '#/components/responses/UpstreamError' '503': $ref: '#/components/responses/ProviderNotConfigured' components: schemas: ChatCompletionRequest: type: object required: - model - messages properties: model: type: string example: openai/gpt-4o-mini messages: type: array items: type: object properties: role: type: string enum: - system - developer - user - assistant - tool content: description: >- A text string, or an array of content parts (text, image_url, input_audio, video_url) for multimodal input. oneOf: - type: string - type: array items: $ref: '#/components/schemas/ChatContentPart' - type: 'null' tool_call_id: type: string description: On `tool` messages the id of the tool call this result is for.: null tool_calls: type: array description: >- On `assistant` messages, tool calls being relayed back to the model. items: $ref: '#/components/schemas/ChatToolCall' stream: type: boolean default: false stream_options: type: object properties: include_usage: type: boolean temperature: type: number top_p: type: number max_tokens: type: integer max_completion_tokens: type: integer tools: type: array description: >- Function tools the model may call (relay mode — the gateway does not execute them). items: $ref: '#/components/schemas/ChatTool' tool_choice: description: >- `auto`, `none`, `required`, or `{ type: function, function: { name } }`. oneOf: - type: string enum: - auto - none - required - type: object properties: type: type: string const: function function: type: object properties: name: type: string parallel_tool_calls: type: boolean reasoning_effort: type: string enum: - none - minimal - low - medium - high - xhigh description: >- Forwarded across native OpenAI, Azure OpenAI, and OpenAI-compatible routes. ChatCompletion: type: object description: Non-streaming chat completion (OpenAI `chat.completion`). properties: id: type: string example: chatcmpl-... object: type: string const: chat.completion created: type: integer description: Unix seconds model: type: string example: openai/gpt-4o-mini choices: type: array items: type: object properties: index: type: integer finish_reason: type: string enum: - stop - length - content_filter - tool_calls nullable: true message: type: object properties: role: type: string const: assistant content: type: string nullable: true tool_calls: type: array description: >- Present when the model called tools (finish_reason `tool_calls`). items: $ref: '#/components/schemas/ChatToolCall' usage: $ref: '#/components/schemas/Usage' ChatCompletionChunk: type: object description: >- One SSE chunk (OpenAI `chat.completion.chunk`), sent as a `data:` line; the stream ends with a `[DONE]` sentinel. properties: id: type: string object: type: string const: chat.completion.chunk created: type: integer model: type: string choices: type: array items: type: object properties: index: type: integer finish_reason: type: string nullable: true delta: type: object description: >- Incremental update — `role` on the first chunk, then `content` deltas, or `tool_calls` fragments. properties: role: type: string content: type: string tool_calls: type: array description: >- Streaming tool-call fragments; `index` correlates fragments of the same call. items: type: object properties: index: type: integer id: type: string type: type: string const: function function: type: object properties: name: type: string arguments: type: string usage: description: >- Present only on the final chunk when `stream_options.include_usage` is true. oneOf: - $ref: '#/components/schemas/Usage' - type: 'null' ChatContentPart: type: object properties: type: type: string enum: - text - image_url - input_audio - video_url text: type: string description: Present when `type` is `text`. image_url: type: object description: Present when `type` is `image_url`. properties: url: type: string description: An http(s) URL or a `data:` base64 URI. detail: type: string enum: - auto - low - high input_audio: type: object description: >- Present when `type` is `input_audio`. Only models advertising `audio` in `input_modalities` accept it. properties: data: type: string description: Base64-encoded audio (no data-URI prefix). format: type: string description: '`wav` or `mp3` (`aiff`, `aac`, `ogg`, `flac` also pass through).' video_url: type: object description: >- Present when `type` is `video_url`. Only models advertising `video` in `input_modalities` accept it. properties: url: type: string description: >- A `data:` base64 URI or an http(s) URL. YouTube URLs pass through to Gemini; other URLs are fetched by the gateway and sent inline (~20MB limit). ChatToolCall: type: object description: >- A complete tool call (non-streaming). `function.arguments` is a JSON-encoded string. properties: id: type: string type: type: string const: function function: type: object properties: name: type: string arguments: type: string description: JSON-encoded arguments string. ChatTool: type: object required: - type - function properties: type: type: string const: function function: type: object required: - name properties: name: type: string description: type: string parameters: type: object description: JSON Schema for the tool input. Usage: type: object description: OpenAI-style token usage. 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 description: >- One of authentication_error, invalid_request_error, insufficient_quota, upstream_error, provider_not_configured. responses: BadRequest: description: Malformed request (bad JSON, or missing required fields). content: application/json: schema: $ref: '#/components/schemas/Error' example: error: message: '`model` and `messages` are required' type: invalid_request_error Unauthorized: description: Missing or invalid API key. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: message: Invalid API key type: authentication_error InsufficientCredits: description: The account's credit balance is empty. Top up to continue. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: message: Insufficient credits. Top up to continue. type: insufficient_quota UnknownModel: description: The requested `model` id is not in the registry (see GET /v1/models). content: application/json: schema: $ref: '#/components/schemas/Error' example: error: message: 'Unknown model: foo/bar' type: invalid_request_error UpstreamError: description: The upstream provider returned an error. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: message: 'permission-denied: ...' type: upstream_error ProviderNotConfigured: description: The provider for this model has no API key configured on the gateway. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: message: 'Provider not configured: missing OPENAI_API_KEY' type: provider_not_configured securitySchemes: BearerKey: type: http scheme: bearer description: Gateway API key (`imp-rt-...`) from POST /v1/accounts or /v1/keys. ````