Short answer: Kling 4.0 Flash and Kling 4.0 both make video with native audio from text, images, reference videos or a video to edit, and both run on EmpirioLabs through one API. Choose Kling 4.0 Flash for faster, lower-cost clips at 720p of up to 20 seconds. Choose Kling 4.0 when you need 1080p, clips of up to 30 seconds, or keyframes: a first, middle and last frame.
Kling 4.0 Flash vs Kling 4.0 at a glance
| Feature | Kling 4.0 Flash | Kling 4.0 |
|---|---|---|
| Maker | Kling AI | Kling AI |
| Resolutions | 720p | 720p, 1080p |
| Clip length | 3 to 20 seconds | 3 to 30 seconds |
| Frames | First frame | First, middle and last frames |
| Reference images | Up to 10 | Up to 10 |
| Reference videos | Up to 5, 20 seconds in total | Up to 5, 3 to 30 seconds each |
| Video editing | 3 to 20 second clips | 3 to 30 second clips |
| Native audio | Yes | Yes |
| Aspect ratios | 16:9, 9:16, 1:1, 21:9 | 16:9, 9:16, 1:1, 21:9 |
| Billing | Per second, a lower rate | Per second, by resolution |
Watch the comparison
Three prompts, run once on each model. Nothing was regenerated or edited.
How we ran it
Three prompts: "A red fox pounces headfirst into deep snow in a pine forest at sunrise, powder bursting into the light, soft crunch of snow and distant birdsong, low tracking shot", "A massive wall of blue glacier ice calves into an arctic sea, huge chunks crashing into the water and sending up a towering splash, thunderous cracking, aerial wide shot" and "A rally car powers sideways over a desert dune at sunset, sand spraying in a golden arc, engine roaring, low tracking shot". Each model got each prompt once, at 720p, 16:9 and 5 seconds, with every other setting at its default, through POST /v1/videos/generations on November 4, 2026. Every clip came back at 1280x720 and about 5 seconds, with a native audio track. From submitting the job to the finished video, Kling 4.0 Flash took a median of 74 seconds and Kling 4.0 a median of 147 seconds; times vary with load.
What to look for
In the fox scene, Kling 4.0 Flash held a wide sunrise view of the forest while Kling 4.0 caught the fox mid-leap, closer to the camera. Both brought the glacier wall down into the sea. In the rally scene, Kling 4.0 Flash buried the car in a dense cloud of sand, and Kling 4.0 framed it against the low sun. Watch the snow and spray, the light, and how each camera follows the motion.
When to use Kling 4.0 Flash
- You want results faster, for drafts, iteration or high volume.
- You want the lower per-second rate and 720p is enough.
- Your clip is 20 seconds or shorter, from text, a first frame, references or a video to edit.
When to use Kling 4.0
- You need 1080p output.
- You need clips longer than 20 seconds, up to 30.
- You want keyframes: a first frame, middle frames and a last frame the clip passes through.
How to call either model
Both use the same asynchronous video API: submit the job, then poll it.
curl -X POST https://api.empiriolabs.ai/v1/videos/generations \
-H "Authorization: Bearer $EMPIRIOLABS_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "kling-4-0-flash",
"prompt": "A red fox pounces headfirst into deep snow in a pine forest at sunrise.",
"resolution": "720p",
"duration": 5
}'
curl https://api.empiriolabs.ai/v1/jobs/JOB_ID \
-H "Authorization: Bearer $EMPIRIOLABS_API_KEY"To run the same request on Kling 4.0, change model to kling-4-0; nothing else changes. You can also try both in the Playground.
Frequently asked questions
Is Kling 4.0 Flash faster than Kling 4.0?
Kling 4.0 Flash is the faster tier. In our one-shot test, a 5 second 720p clip took a median of 74 seconds on Kling 4.0 Flash and 147 seconds on Kling 4.0, from submitting the job to the finished video.
Which one costs less?
Kling 4.0 Flash has the lower per-second rate. Both bill per second of video, and a request with a video input bills at a separate video input rate. Current rates are on each model page and the pricing page.
Can Kling 4.0 Flash use a last frame or keyframes?
No. Kling 4.0 Flash takes a first frame only. For a last frame or middle frames, use Kling 4.0.
Do both generate audio?
Yes. Both return a native audio track with every clip.
How do I switch between them in code?
Change the model id between kling-4-0-flash and kling-4-0. The request and response are the same. Kling 4.0 Flash accepts 720p only.
Try it
Run either model in the Playground, compare every video model on the models page, or see current rates on the pricing page.
