> ## Documentation Index > Fetch the complete documentation index at: https://docs.priorlabs.ai/llms.txt > Use this file to discover all available pages before exploring further. # Fit (TabPFN JSON API) > **Recommended:** Use [tabpfn-client](https://github.com/PriorLabs/tabpfn-client) (`TabPFNClassifier` / `TabPFNRegressor`). It calls these routes for you. JSON body after you upload train files via `POST /tabpfn/prepare_train_set_upload` and PUT the returned signed URLs. Returns `fitted_train_set_id`. Long fits may stream JSON with leading keepalive whitespace; see the [TabPFN-3 changelog](/changelog/tabpfn-3). Key fields: `train_set_upload_id` (UUID), `task` (`classification` | `regression`), `tabpfn_systems`, optional `tabpfn_config`, `thinking_effort` (`medium` | `high` or omit), `thinking_timeout_s`, `thinking_effort_metric`, `force_refit`. ## OpenAPI ````yaml /api-reference/openapi.json post /tabpfn/fit openapi: 3.1.0 info: title: TabPFN API description: >- Prior Labs TabPFN API. **Prefer [tabpfn-client](https://github.com/PriorLabs/tabpfn-client)**. Current integration surface: **`/tabpfn/*` JSON routes** (prepare uploads, fit, predict, limits). **`/v1/*` multipart routes are deprecated.** See the [Changelog](/changelog). version: 2.0.0 contact: name: Prior Labs email: hello@priorlabs.ai servers: - url: https://api.priorlabs.ai description: Production TabPFN API (`/tabpfn/*` current; `/v1/*` deprecated) security: - BearerAuth: [] paths: /tabpfn/fit: post: tags: - Training summary: Fit (TabPFN JSON API) description: >- **Recommended:** Use [tabpfn-client](https://github.com/PriorLabs/tabpfn-client) (`TabPFNClassifier` / `TabPFNRegressor`). It calls these routes for you. JSON body after you upload train files via `POST /tabpfn/prepare_train_set_upload` and PUT the returned signed URLs. Returns `fitted_train_set_id`. Long fits may stream JSON with leading keepalive whitespace; see the [TabPFN-3 changelog](/changelog/tabpfn-3). Key fields: `train_set_upload_id` (UUID), `task` (`classification` | `regression`), `tabpfn_systems`, optional `tabpfn_config`, `thinking_effort` (`medium` | `high` or omit), `thinking_timeout_s`, `thinking_effort_metric`, `force_refit`. operationId: tabpfn_fit requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/FitRequest' example: train_set_upload_id: 123e4567-e89b-12d3-a456-426614174000 task: classification tabpfn_systems: - preprocessing - text thinking_effort: medium responses: '200': description: >- Fitted train set id (JSON; may be streamed with leading whitespace on long fits). content: application/json: schema: $ref: '#/components/schemas/TabpfnFitResponse' '401': description: >- Unauthorized — authentication required or credentials invalid. **Possible causes:** - Missing or malformed `Authorization` header - Invalid or expired JWT token - User not found (token references a deleted account) - JWT decode errors (JWEDecodeError, JWTDecodeError, JWTClaimsError) **Examples:** - Missing token: `{"detail": "Not authenticated"}` - Invalid credentials: `{"detail": "Could not validate credentials"}` content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' examples: missing_token: value: code: auth.unauthorized detail: Not authenticated retryable: false support: https://discord.com/invite/VJRuU3bSxt invalid_credentials: value: code: auth.unauthorized detail: Could not validate credentials retryable: false support: https://discord.com/invite/VJRuU3bSxt expired_token: value: code: auth.unauthorized detail: Invalid or expired JWT token retryable: false support: https://discord.com/invite/VJRuU3bSxt '404': description: >- Model not found — the provided model ID does not exist or has expired. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: code: error.not_found detail: >- Fitted model with ID 123e4567-e89b-12d3-a456-426614174000 not found retryable: false support: https://discord.com/invite/VJRuU3bSxt '422': description: Validation error — one or more fields are incorrectly formatted. content: application/json: schema: $ref: '#/components/schemas/ValidationError' '429': description: Quota exceeded (predict pre-check or thinking-fit monthly limit). security: - BearerAuth: [] components: schemas: FitRequest: properties: train_set_upload_id: type: string format: uuid title: Train Set Upload Id task: $ref: '#/components/schemas/PredictionTask' tabpfn_systems: items: type: string enum: - preprocessing - text - thinking type: array title: Tabpfn Systems default: - preprocessing - text tabpfn_config: anyOf: - additionalProperties: true type: object - type: 'null' title: Tabpfn Config thinking_effort: anyOf: - type: string enum: - medium - high - type: 'null' title: Thinking Effort thinking_timeout_s: anyOf: - type: number - type: 'null' title: Thinking Timeout S thinking_effort_metric: anyOf: - type: string - type: 'null' title: Thinking Effort Metric force_refit: type: boolean title: Force Refit description: >- Whether to force the fitting of the train set even if a fittedtrain set and transform states already exist. default: false additionalProperties: false type: object required: - train_set_upload_id - task title: FitRequest TabpfnFitResponse: type: object required: - fitted_train_set_id properties: fitted_train_set_id: type: string format: uuid ErrorResponse: type: object required: - code - detail - retryable - support properties: code: type: string description: Error category code (e.g., auth.unauthorized, rate.limit.exceeded) example: auth.unauthorized detail: type: string description: Human-readable error message describing what went wrong. example: Invalid authentication credentials retryable: type: boolean description: Indicates whether the request can be retried. example: false support: type: string description: URL to get support for this error. example: https://discord.com/invite/VJRuU3bSxt example: code: auth.unauthorized detail: Invalid authentication credentials retryable: false support: https://discord.com/invite/VJRuU3bSxt ValidationError: type: object required: - code - detail - errors - retryable - support properties: code: type: string description: Error category code for validation errors example: validation.failed detail: type: string description: Human-readable validation error message example: Validation error for FitRequest errors: type: array description: Array of field-level validation errors items: type: object properties: field: type: string description: Field name where the error occurred example: task message: type: string description: Error message for this field example: field required retryable: type: boolean description: Indicates whether the request can be retried example: false support: type: string description: URL to get support for this error example: https://discord.com/invite/VJRuU3bSxt example: code: validation.failed detail: Validation error for FitRequest errors: - field: task message: field required - field: systems message: >- Invalid system: invalid_system. Must be one of: ['preprocessing', 'text'] retryable: false support: https://discord.com/invite/VJRuU3bSxt PredictionTask: type: string enum: - classification - regression description: >- Specifies the type of task to perform — either classification or regression. securitySchemes: BearerAuth: type: http scheme: bearer bearerFormat: JWT description: >- Bearer token for authentication, obtained after signing up and generating an API key. ````