> ## Documentation Index > Fetch the complete documentation index at: https://docs.zerogpu.ai/llms.txt > Use this file to discover all available pages before exploring further. # Responses > Send input to an AI model and receive a response. One endpoint for every model. Pass text or a document as `input`; what comes back depends on the model: generated text, a classification, extracted fields, redacted output, and more. The `input` and `output` shapes vary by model, so open a [model page](/api-reference/models) for a prefilled playground. For the `messages`-style route, see [Chat completions](/api-reference/chat-completions). Install the official SDK from [npm](https://www.npmjs.com/package/zerogpu-api) or [PyPI](https://pypi.org/project/zerogpu-api/) (`pip install zerogpu-api`). Source: [zerogpu/SDK](https://github.com/zerogpu/SDK). Handle errors the same way as [API error codes](/docs/production-patterns#handle-status-codes-explicitly). ## OpenAPI ````yaml api-reference/openapi/zerogpu.openapi.json POST /responses openapi: 3.1.0 info: title: ZeroGPU API version: '1.0' description: >- REST API for ZeroGPU model inference: `POST /v1/responses` and `POST /v1/chat/completions` (model-dependent). Authentication uses `x-api-key` and `x-project-id` headers on every request. Documentation: https://docs.zerogpu.ai **Per-model playgrounds** are listed on [Model playgrounds](/api-reference/models) with request examples for each model's use cases. These endpoint pages show a generic shape only. servers: - url: https://api.zerogpu.ai/v1 description: Production security: - ApiKey: [] ProjectId: [] paths: /responses: post: tags: - Responses summary: Create response operationId: createResponse requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/CreateResponseRequest' example: model: llama-3.1-8b-instruct-fast input: >- NASA announced that its Artemis III mission is now scheduled for late 2026, marking the first time astronauts will land on the lunar surface since Apollo 17 in 1972. The mission will send a crew of four to the Moon aboard the Orion spacecraft, with two astronauts descending to the south pole using SpaceX Starship as a lunar lander. Scientists are particularly excited about exploring permanently shadowed craters that may contain water ice, which could be critical for sustaining long-term human presence on the Moon. responses: '200': description: Success content: application/json: schema: $ref: '#/components/schemas/Response' example: id: resp_abc123 object: response created: 1710000000 model: llama-3.1-8b-instruct-fast output: - type: message role: assistant content: - type: output_text text: >- Artemis III, slated for late 2026, will return astronauts to the Moon for the first time since 1972, landing two crew at the south pole to study shadowed craters that may hold water ice. usage: input_tokens: 112 output_tokens: 44 total_tokens: 156 '400': description: Bad request (invalid body) '401': description: Unauthorized (invalid or missing API key) '403': description: Forbidden (invalid project ID or permissions) '420': description: Insufficient quota (insufficient_quota) content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: code: insufficient_quota message: You have insufficient quota to complete this request. '500': description: Internal server error components: schemas: CreateResponseRequest: type: object required: - model - input properties: model: type: string description: >- Model identifier. Open a [model page](/api-reference/models) for a dedicated playground with the correct body for that model. enum: - llama-3.1-8b-instruct-fast - LFM2.5-1.2B-Instruct - LFM2.5-1.2B-Thinking - deberta-v3-small - gliner2-base-v1 - gliner-multi-pii-v1 - zlm-v1-followup-questions-edge - zlm-v1-iab-classify-edge - zlm-v1-iab-classify-edge-enriched example: llama-3.1-8b-instruct-fast input: type: string minLength: 1 format: textarea maxLength: 131072 description: The text or document to send, as a plain string. text: type: object description: Response format configuration. properties: format: type: object properties: type: type: string description: Output format for the response, for example `text`. example: text instructions: type: string description: >- Optional system-style instructions applied on top of `input`, for models that support them. metadata: type: object additionalProperties: true description: >- Optional model-specific parameters, passed through to the model. For example, PII models accept `mask` and `usecase`. See the relevant [model page](/api-reference/models) for supported keys. Response: type: object description: The generated model response. properties: id: type: string description: Unique identifier for the response. example: resp_abc123 object: type: string description: Object type. Always `response`. example: response created: type: integer description: Unix timestamp (seconds) when the response was created. example: 1710000000 model: type: string description: The model used for inference. example: llama-3.1-8b-instruct-fast output: type: array description: Output message objects produced by the model. items: $ref: '#/components/schemas/OutputMessage' usage: $ref: '#/components/schemas/Usage' ErrorResponse: type: object description: Error payload returned on a failed request. properties: error: type: object properties: code: type: string description: Machine-readable error code, for example `insufficient_quota`. example: insufficient_quota message: type: string description: Human-readable description of the error. example: You have insufficient quota to complete this request. OutputMessage: type: object description: A single output item from the model. properties: type: type: string description: Output item type. example: message role: type: string description: Author of the output. Always `assistant`. example: assistant content: type: array description: Content parts that make up the message. items: type: object properties: type: type: string description: Content part type. example: output_text text: type: string description: The generated text. example: >- Artemis III, slated for late 2026, will return astronauts to the Moon for the first time since 1972. Usage: type: object description: Token usage statistics for the request. properties: input_tokens: type: integer description: Number of tokens in the input. example: 112 output_tokens: type: integer description: Number of tokens generated. example: 44 total_tokens: type: integer description: Total tokens consumed (input plus output). example: 156 securitySchemes: ApiKey: type: apiKey in: header name: x-api-key description: >- Your ZeroGPU API key. Create one in the dashboard under API keys. Send it on every request. ProjectId: type: apiKey in: header name: x-project-id description: >- The UUID of the project the request is billed to. Find it in the dashboard project settings. ````