> ## Documentation Index
> Fetch the complete documentation index at: https://langwatch.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Create Run

> Start execution of a saved Evaluations V3 experiment by slug. Returns immediately with a runId for polling, or streams SSE events if Accept: text/event-stream header is provided.



## OpenAPI

````yaml POST /api/evaluations/v3/{slug}/run
openapi: 3.1.0
info:
  title: LangWatch API
  version: 1.0.0
  description: LangWatch openapi spec
servers:
  - url: https://app.langwatch.ai
security:
  - project_api_key: []
paths:
  /api/evaluations/v3/{slug}/run:
    post:
      tags:
        - Evaluations V3
      description: >-
        Start execution of a saved Evaluations V3 experiment by slug. Returns
        immediately with a runId for polling, or streams SSE events if Accept:
        text/event-stream header is provided.
      operationId: postEvaluationsV3Run
      parameters:
        - schema:
            type: string
          in: path
          name: slug
          required: true
          description: The slug of the evaluation to run
      responses:
        '200':
          description: Run started successfully
          content:
            application/json:
              schema:
                type: object
                properties:
                  runId:
                    type: string
                    description: Unique identifier for this run
                  status:
                    type: string
                    enum:
                      - running
                    description: Initial status of the run
                  total:
                    type: integer
                    description: Total number of cells to execute
                  runUrl:
                    type: string
                    description: URL to view the run in LangWatch
                required:
                  - runId
                  - status
                  - total
            text/event-stream:
              schema:
                type: string
                description: Server-sent events stream with execution progress
        '401':
          description: Unauthorized - Missing or invalid API key
          content:
            application/json:
              schema:
                type: object
                properties:
                  error:
                    type: string
                required:
                  - error
        '404':
          description: Evaluation not found
          content:
            application/json:
              schema:
                type: object
                properties:
                  error:
                    type: string
                required:
                  - error
components:
  securitySchemes:
    project_api_key:
      type: apiKey
      in: header
      name: X-Auth-Token
      description: >-
        Project API key for sending traces and accessing project-scoped
        resources. Format: sk-lw-... (no underscore). Obtain one by creating a
        project via the Admin API or the LangWatch UI.

````