Veo 3.1 Fast API: Faster Google Video Generation

Google Veo 3.1 Fast on Genflo: a quicker, lower-cost Veo 3.1 for 8-second videos with native audio from text, an image, or first and last frames.

Complete request

This copy-ready shape includes every input field published for this model.

curl -X POST 'https://api.genflo.io/api/saas' \
  -H 'Content-Type: application/json' \
  -H 'x-apikey: sk-your-api-key' \
  -d '{
    "model": "gv-3.1-fast",
    "input": {
      "prompt": "The camera slowly moves forward while the subject turns toward the light",
      "negative_prompt": "blur, distortion, artifacts",
      "enhance_prompt": true,
      "images": [
        "https://cdn.example.com/reference-image.jpg"
      ],
      "first_frame": "https://cdn.example.com/first-frame.jpg",
      "last_frame": "https://cdn.example.com/last-frame.jpg",
      "duration": 8,
      "resolution": "720P",
      "aspect_ratio": "16:9",
      "generate_audio": true,
      "seed": 123456789
    }
  }'

Optional fields may be removed. The complete example demonstrates the JSON wire format; the upstream model may reject incompatible mode combinations, such as mixing frame animation with unrelated reference media.

How media fields are transmitted

Send media as public URL strings inside the JSON body—not as multipart uploads. A plural field such as videos is an array, for example ["https://cdn.example.com/reference.mp4"].

images → Image / Reference
videos → Video / Reference
audios → Audio / Reference
first_frame → Image / FirstFrame

Input parameters

11 fields are published for this model. Omitted optional fields are not sent upstream and have no gateway-defined default.

Field	Required	JSON type	Description and constraints	Example
`prompt`	Optional	`string`	The main instruction describing the output to generate.	`"The camera slowly moves forward while the subject turns toward the light"`
`negative_prompt`	Optional	`string`	Content and visual qualities the model should avoid.	`"blur, distortion, artifacts"`
`enhance_prompt`	Optional	`boolean`	Ask the upstream model to expand and optimize the prompt before generation.	`true`
`images`	Optional	`string[]`	Publicly reachable reference or source image URLs. Items: 0 to 1 · Formats: jpg, jpeg, png, webp	`["https://cdn.example.com/reference-image.jpg"]`
`first_frame`	Optional	`string`	A public image URL used as the first frame of the generated video. Formats: jpg, jpeg, png, webp	`"https://cdn.example.com/first-frame.jpg"`
`last_frame`	Conditional	`string`	A public image URL used as the final frame. Use it together with first_frame. Formats: jpg, jpeg, png, webp · Maximum size: 5 MB	`"https://cdn.example.com/last-frame.jpg"`
`duration`	Required	`number enum`	Requested video duration in seconds. It is also used to calculate the task charge. Allowed: 8	`8`
`resolution`	Optional	`string enum`	Requested output resolution. Values are model-specific and case-sensitive at this API boundary. Allowed: 720P, 1080P, 2K, 4K	`"720P"`
`aspect_ratio`	Optional	`string enum`	Requested output width-to-height ratio. Allowed: 16:9, 9:16	`"16:9"`
`generate_audio`	Optional	`boolean`	Whether the upstream model should generate an audio track with the video.	`true`
`seed`	Optional	`integer`	Integer random seed. Reusing a seed can improve reproducibility, but identical output is not guaranteed.	`123456789`

Video requests require input.duration. The final charge is the per-second rate multiplied by duration.