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

# Initiate Multipart Upload

> Start a multipart upload for a large file. `fileUrl` is the canonical public URL — keep it; it is the one to pass as a model input once the upload completes.



## OpenAPI

````yaml /platform-openapi.json post /storage/upload/initiate-multipart
openapi: 3.1.0
info:
  title: ModelRunner Platform API
  version: 1.0.0
  description: >-
    Platform APIs: model catalog, search and collections; model pricing rate
    cards; the Serverless GPU catalog and deployment templates; file uploads and
    your asset library; account balance and usage; and webhook delivery
    management. Catalog reads are public; account-scoped routes authenticate
    with your API key (`Authorization: Key <MODELRUNNER_KEY>`). Request
    lifecycle endpoints (submit/status/result and the request list) live on the
    queue host — see the Queue API reference.
servers:
  - url: https://api.modelrunner.run
security: []
paths:
  /storage/upload/initiate-multipart:
    post:
      summary: Initiate Multipart Upload
      description: >-
        Start a multipart upload for a large file. `fileUrl` is the canonical
        public URL — keep it; it is the one to pass as a model input once the
        upload completes.
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              required:
                - file_name
                - content_type
              properties:
                file_name:
                  type: string
                content_type:
                  type: string
                size:
                  type: integer
      responses:
        '200':
          description: Multipart upload started.
          content:
            application/json:
              schema:
                type: object
                properties:
                  fileUrl:
                    type: string
                    description: Canonical public URL for the finished object.
                  uploadId:
                    type: string
                  uploadKey:
                    type: string
        '401':
          description: Missing or invalid credentials.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
      security:
        - apiKeyAuth: []
components:
  schemas:
    ErrorResponse:
      type: object
      properties:
        error:
          type: string
          description: Human-readable error message.
        request_id:
          type: string
          description: Correlation id for support.
  securitySchemes:
    apiKeyAuth:
      type: apiKey
      in: header
      name: Authorization
      description: 'Use the format: Key modelrunner_key'

````