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

# Veo 3.1 Fast I2V

> [Core Function] Veo 3.1 Fast I2V is a high-speed image-to-video model. [Strengths] It quickly animates starting images at 1080p, optimized for low latency. [Best For] Highly recommended for: rapid prototyping and quick social media visual iterations. [Limitations] Do NOT use this model for the absolute highest visual fidelity or 4K output. [Routing] Choose this model when the user emphasizes 'fast' or 'quick' animation.



## OpenAPI

````yaml /model-api/google/google-i2v.json post /google/veo-3.1-fast-i2v
openapi: 3.1.0
info:
  description: The image-to-video models API from Google (Veo series).
  version: 1.0.0
  contact:
    name: Modellix Support
    email: support@modellix.ai
  title: Google Image-to-Video Models API
servers:
  - url: https://api.modellix.ai/api/v1
    description: The image-to-video models API from Google.
security:
  - bearerAuth: []
paths:
  /google/veo-3.1-fast-i2v:
    post:
      summary: Veo 3.1 Fast I2V
      description: >-
        [Core Function] Veo 3.1 Fast I2V is a high-speed image-to-video model.
        [Strengths] It quickly animates starting images at 1080p, optimized for
        low latency. [Best For] Highly recommended for: rapid prototyping and
        quick social media visual iterations. [Limitations] Do NOT use this
        model for the absolute highest visual fidelity or 4K output. [Routing]
        Choose this model when the user emphasizes 'fast' or 'quick' animation.
      operationId: veo31FastI2VAsync
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/Veo31I2VRequest'
            examples:
              image_mode_basic:
                summary: Image mode — basic animation
                value:
                  prompt: Gentle breeze causes leaves to rustle in the scene
                  image: https://example.com/frame.jpg
              image_mode_options:
                summary: Image mode — with duration and resolution
                value:
                  prompt: Camera slowly pans across the landscape
                  image: https://example.com/frame.jpg
                  aspectRatio: '16:9'
                  duration: '6'
                  resolution: 720p
              reference_mode:
                summary: Reference mode — reference images (duration must be 8)
                value:
                  prompt: Keep the same character and visual style
                  referenceImages:
                    - https://example.com/ref.jpg
                  aspectRatio: '16:9'
                  duration: '8'
                  resolution: 720p
      responses:
        '200':
          description: Task submitted successfully
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/AsyncTaskResponse'
              example:
                code: 0
                message: success
                data:
                  status: pending
                  task_id: task-i2v002
                  model_id: google/veo-3.1-fast-i2v
                  get_result:
                    method: GET
                    url: https://api.modellix.ai/api/v1/tasks/task-i2v002
        '400':
          $ref: '#/components/responses/BadRequest'
        '401':
          $ref: '#/components/responses/Unauthorized'
        '429':
          $ref: '#/components/responses/TooManyRequests'
        '500':
          $ref: '#/components/responses/InternalServerError'
components:
  schemas:
    Veo31I2VRequest:
      description: >-
        Veo 3.1 / Veo 3.1 Fast image-to-video request. Choose one option —
        `image` mode and `referenceImages` mode are mutually exclusive.
        Resolution up to 4K. Constraints verified 2026-04-29 against Google raw
        API, see each parameter for details.
      oneOf:
        - $ref: '#/components/schemas/Veo31I2VImageOption'
          title: Option 1 — Image mode
          description: Animate from a starting frame, optionally to an end frame.
        - $ref: '#/components/schemas/Veo31I2VReferenceOption'
          title: Option 2 — Reference mode
          description: Guide generation with reference images (style/character/visual).
    AsyncTaskResponse:
      type: object
      required:
        - code
        - message
        - data
      properties:
        code:
          type: integer
          description: Response code, 0 indicates success
          example: 0
        message:
          type: string
          description: Response message
          example: success
        data:
          type: object
          required:
            - status
            - task_id
            - model_id
          properties:
            status:
              type: string
              enum:
                - pending
                - processing
              description: Task status
              example: pending
            task_id:
              type: string
              description: Unique task identifier for polling
              example: task-abc123
            model_id:
              type: string
              description: Model ID in `provider/model` format
              example: google/veo-3.1-i2v
            get_result:
              type: object
              description: API information to query the task result
              properties:
                method:
                  type: string
                  description: HTTP method
                  example: GET
                url:
                  type: string
                  description: Full URL to query the task result
                  example: https://api.modellix.ai/api/v1/tasks/task-abc123
          description: Detailed data about the submitted asynchronous task.
    Veo31I2VImageOption:
      type: object
      required:
        - prompt
        - image
      description: >-
        Veo 3.1 / Veo 3.1 Fast I2V — image mode. Animate from a starting frame.
        Cannot be combined with `referenceImages`.
      properties:
        prompt:
          type: string
          description: Video description text guiding the animation
          minLength: 1
          example: The character waves and smiles at the camera
        image:
          type: string
          description: >-
            Starting frame. Accepts an image URL (e.g.
            `https://example.com/frame.jpg`).
          example: https://example.com/frame.jpg
        lastFrame:
          type: string
          description: >-
            End frame. Accepts an image URL. Constraint: `duration` must be `8`
            when using this parameter.
          example: https://example.com/last-frame.jpg
        negativePrompt:
          type: string
          description: Text describing what to avoid in the generated video.
          example: blurry, low quality, distorted
        aspectRatio:
          type: string
          description: Video aspect ratio
          default: '16:9'
          enum:
            - '16:9'
            - '9:16'
          example: '16:9'
        duration:
          type: string
          description: >-
            Video duration in seconds (string type). Constraint: When using
            `lastFrame`, must be `8` — values `4` or `6` will be rejected by
            Google. Otherwise `4`, `6`, `8` are all valid.
          enum:
            - '4'
            - '6'
            - '8'
          example: '8'
        resolution:
          type: string
          description: >-
            Video resolution. Constraint: 1080p and 4k are only available when
            `duration` is `8`.
          enum:
            - 720p
            - 1080p
            - 4k
          example: 1080p
        personGeneration:
          type: string
          description: Person generation policy
          enum:
            - allow_adult
          example: allow_adult
    Veo31I2VReferenceOption:
      type: object
      required:
        - prompt
        - referenceImages
      description: >-
        Veo 3.1 / Veo 3.1 Fast I2V — reference mode. Guide generation with
        reference images. Cannot be combined with `image`, `lastFrame`, or
        `negativePrompt`.
      properties:
        prompt:
          type: string
          description: Video description text guiding the animation
          minLength: 1
          example: The character waves and smiles at the camera
        referenceImages:
          type: array
          description: >-
            Reference images for style/character/visual guidance (up to 3). Each
            item is an image URL (e.g. `https://example.com/ref.jpg`). Supported
            only by Veo 3.1 and Veo 3.1 Fast I2V.
          items:
            type: string
          maxItems: 3
          example:
            - https://example.com/ref.jpg
        aspectRatio:
          type: string
          description: Video aspect ratio
          default: '16:9'
          enum:
            - '16:9'
            - '9:16'
          example: '16:9'
        duration:
          type: string
          description: >-
            Video duration in seconds (string type). Constraint: Must be `8` in
            reference mode — values `4` or `6` will be rejected by Google.
          enum:
            - '8'
          example: '8'
        resolution:
          type: string
          description: >-
            Video resolution. Constraint: 1080p and 4k are only available when
            `duration` is `8`.
          enum:
            - 720p
            - 1080p
            - 4k
          example: 1080p
        personGeneration:
          type: string
          description: Person generation policy
          enum:
            - allow_adult
          example: allow_adult
    ErrorResponse:
      type: object
      required:
        - code
        - message
      properties:
        code:
          type: integer
          description: Error code (equals HTTP status code)
          example: 400
        message:
          type: string
          description: 'Error message in format ''Category: detail'''
          example: 'Invalid parameters: parameter ''prompt'' is required'
  responses:
    BadRequest:
      description: Invalid request parameters
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorResponse'
          example:
            code: 400
            message: 'Invalid parameters: parameter ''prompt'' is required'
    Unauthorized:
      description: Unauthorized - Invalid or missing API Key
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorResponse'
          example:
            code: 401
            message: 'Authentication failed: invalid API key'
    TooManyRequests:
      description: Too many requests - Rate limit exceeded
      headers:
        X-RateLimit-Limit:
          description: Maximum requests per minute
          schema:
            type: integer
            example: 100
        X-RateLimit-Remaining:
          description: Remaining quota in current window
          schema:
            type: integer
            example: 0
        X-RateLimit-Reset:
          description: Rate limit window reset time (Unix timestamp)
          schema:
            type: integer
            example: 1704067260
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorResponse'
          example:
            code: 429
            message: >-
              Rate limit exceeded: 100 requests per minute, retry after 60
              seconds
    InternalServerError:
      description: Internal server error
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorResponse'
          example:
            code: 500
            message: Internal server error
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      description: 'API Key authentication. Format: `Bearer YOUR_API_KEY`.'

````