POST /api/v1/videos/generations with model: kling-4-0-flash, optionally with a first frame in image_url, and get a 720p single take of 3 to 20 seconds with a native audio track. Track the job with the returned img_uuid.Kling 4.0 Flash API for Fast 720p Video with Sound
Kling 4.0 Flash is the faster, lower-cost version of Kling 4.0. Send a prompt to
Get API Key
Kling 4.0 Speed at a Lower Price
Single takes up to 20 seconds
duration takes any integer from 3 to 20 (default 5), so one request can cover a full shot.
Start from a first frame
Pass
image_url to animate your image; the aspect ratio follows it. Images up to 10MB, at least 300px wide and tall, between 2:5 and 5:2.
Audio included in every clip
Each video comes with a native audio track. There is no switch, so
sound / generate_audio are rejected.
A prompt is required; a first frame switches to image-to-video.
Kling 4.0 Flash Request Fields and Limits
model
Always
kling-4-0-flash.prompt (required)
Scene, motion and camera, up to 2500 characters.
image_url
Optional first frame. Up to 10MB, width and height at least 300px, aspect ratio between 2:5 and 5:2; smaller images are upscaled automatically.
duration, resolution and ratio
duration: integer 3-20, default 5. resolution: 720p only. ratio: 16:9 (default), 9:16, 1:1 or 21:9, text-to-video only.Rejected fields
image_end_url and keyframes (use Kling 4.0), reference images or videos (use Kling 4.0 Flash Reference to Video), sound / generate_audio, negative_prompt, seed, model_params.multi_shot and 1080p / 4K are rejected before any tokens are charged.custom_callback_url
Optional public HTTPS URL. GoEnhance POSTs the same body as
GET /api/v1/jobs/detail when the task status changes, with up to 3 retries.Billed per second of generated video; text-to-video and image-to-video cost the same.
Kling 4.0 Flash API Pricing
720p: 5.5715 tokens ($0.11143) per second
The only resolution for this model.
5-second clip
27.86 tokens ($0.5572).
20-second clip
111.43 tokens ($2.2286).
Integrate the Kling 4.0 Flash API
2
2. Prepare the request
POST
model, prompt and an optional image_url to /api/v1/videos/generations. 3
3. Store img_uuid
Keep the returned
img_uuid and poll GET /api/v1/jobs/detail, or pass custom_callback_url. 4
4. Save the video
When the status is
success, download the video and store it on your side.High-volume clips where 720p is enough.
What Developers Build with Kling 4.0 Flash
Social clip generators
Turn a prompt into a vertical
9:16 clip with sound for short-video apps.Photo animation
Animate a user's photo from
image_url into a 3-20 second shot.Draft before a final render
Iterate on prompts with Flash, then send the chosen version to Kling 4.0 for 1080p or last-frame control.
Cinematic widescreen shots
Use
21:9 for banner and trailer-style shots from text.Common questions about requests and billing.
Kling 4.0 Flash API FAQ
How is Kling 4.0 Flash different from Kling 4.0?
Flash is faster and costs less, but outputs 720p only, up to 20 seconds, and takes a first frame only: no last frame or middle keyframes.
Can I turn the audio off?
No. Every clip includes native audio and sound / generate_audio are rejected.
Can I set the aspect ratio for image-to-video?
No. With image_url the output follows your image and ratio is ignored.
Can I use reference images or videos?
Use the kling-4-0-flash-refs model for references, and kling-4-0-flash-edit to edit a video.
What happens if I send 1080p?
The request is rejected before any tokens are charged; only 720p is supported.