Kling 4.0 Flash vs Kling 4.0 on WaveSpeedAI: Which One to Use

Kling 4.0 Flash and Kling 4.0 are both live on WaveSpeedAI. Flash is the fast, lower-cost tier: 720p clips of 3 to 20 seconds with synchronized audio. Kling 4.0 is the full model: 720p or 1080p, clips up to 30 seconds, and video extend. Any WaveSpeedAI account can use either one with per-second billing and no subscription.

What Did Kling Publish About Flash?

These points are Kling’s own statements about Kling’s own product.

Kling’s official LinkedIn update says Flash went live first for Ultra Yearly subscribers. The official Kling 4.0 release note says early access began on 28 September 2026 for a limited group of users.

Kling positions Flash as the faster, value-oriented member of the 4.0 lineup. Its published table lists text-to-video, image-to-video, Omni Reference, 3 to 20 second clips, 720p output, and 8-bit SDR. Kling’s full 4.0 overview is at kling.ai/blog/kling-4-ai-video-model.

Commercial use on Kling’s platform follows Kling’s terms. The Kling AI Terms of Service include written-permission language for commercial use and output-labeling requirements. Check them before client delivery. This is not legal advice.

Which Kling 4.0 Flash Models Are on WaveSpeedAI?

Kling 4.0 Flash has four endpoints. Start from the Kling 4.0 API page, which lists both Flash and Kling 4.0.

Endpoint	What it does
text-to-video	Prompt in, clip out. Aspect ratio 16:9 (default), 9:16, 1:1 or 21:9.
image-to-video	Animates a required first-frame image. The prompt is optional.
reference-to-video	Up to 10 reference images and 5 reference videos, cited in the prompt as @Image1, @Video1. Reference videos guide motion, camera and pacing.
video-edit	Changes an existing 3 to 20 second video from a prompt while keeping the scene, subject and motion, with up to 10 optional reference images.

All four produce 720p clips of 3 to 20 seconds (whole seconds, default 5) with synchronized audio. Reference-to-video and video-edit can keep the source video’s own sound instead of generating new audio.

Which Kling 4.0 Models Are on WaveSpeedAI?

Kling 4.0 has five endpoints:

Endpoint	What it does
text-to-video	Prompt in, clip out. Aspect ratio 16:9 (default), 9:16, 1:1 or 21:9.
image-to-video	A required first frame, plus optional last frame and in-between keyframes (at most 10 images in total).
reference-to-video	Up to 10 reference images, 5 reference videos and 3 reference audios (15 files at most), cited in the prompt as @Image1, @Video1, @Audio1.
video-edit	Changes an existing 3 to 30 second video from a prompt while keeping the scene, subject and motion.
video-extend	Generates a new segment of 3 to 30 seconds from the last frame of a video and returns the original and the new segment joined.

All five produce clips of 3 to 30 seconds (whole seconds, default 5) at 720p (default) or 1080p, with synchronized stereo audio generated with the picture. There is no 4K tier, no 120-second mode, and no Image 4.0 endpoint on WaveSpeedAI. Kling 3.0 and Kling O3 are the models with native 4K tiers there.

You can also use both in the browser. The Video Generator offers Kling 4.0 Flash and Kling 4.0.

Kling 4.0 Flash vs Kling 4.0 on WaveSpeedAI

	Kling 4.0 Flash	Kling 4.0
Best for	Drafts, iteration and high-volume clips	Final shots and longer scenes
Modes	Text-to-video, image-to-video, reference-to-video, video edit	The same four, plus video extend
Clip length	3 to 20 seconds	3 to 30 seconds
Resolution	720p	720p or 1080p
Image-to-video frames	First frame	First frame, optional last frame and keyframes
References	Up to 10 images and 5 videos	Up to 10 images, 5 videos and 3 audios
Audio	Synchronized audio generated with the picture	Synchronized stereo audio generated with the picture
Price	Lower per second	Higher per second
Access	API and browser Video Generator	API and browser Video Generator

How Are Kling 4.0 Flash and Kling 4.0 Priced on WaveSpeedAI?

Billing is per second of generated video, with no subscription. At the time of writing:

Model	Endpoint	Price
Kling 4.0 Flash	text-to-video, image-to-video, reference-to-video without reference videos	$0.094/s
Kling 4.0 Flash	reference-to-video with reference videos	$0.126/s
Kling 4.0 Flash	video-edit	$0.126 per second of the input video
Kling 4.0	text-to-video, image-to-video, video-extend	$0.157/s at 720p, $0.235/s at 1080p
Kling 4.0	reference-to-video with reference videos, and video-edit	$0.094 per counted second at 720p, $0.141 at 1080p

Examples: a 5 second Flash clip is $0.47, a 5 second 720p Kling 4.0 clip is $0.785, and a 10 second 1080p Kling 4.0 clip is $2.35. For Kling 4.0, reference-to-video without a reference video uses the same per-second price as text-to-video. With reference videos, and for video-edit, a counted second is the output length plus the longer of the output length and the total reference-video length, each capped at 30 seconds. An output as long as the reference videos therefore costs $0.188/s at 720p and $0.282/s at 1080p. Reference audios are not charged. For video-extend, only the new segment is generated and charged. Check the Kling 4.0 API page for current prices.

How Do You Call It?

The request pattern is the same as the other Kling models: POST to https://api.wavespeed.ai/api/v3/<model id>, take the prediction id from the response, and poll for the result. This example calls Flash. For Kling 4.0, change the model id to kwaivgi/kling-v4.0/text-to-video and add "resolution": "720p" or "1080p".

curl -X POST "https://api.wavespeed.ai/api/v3/kwaivgi/kling-v4.0-flash/text-to-video" \
  -H "Authorization: Bearer $WAVESPEED_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"prompt": "A red ceramic mug on a wooden table, a hand lifts it once, slow push-in", "aspect_ratio": "16:9", "duration": 5}'

curl "https://api.wavespeed.ai/api/v3/predictions/<id>/result" \
  -H "Authorization: Bearer $WAVESPEED_API_KEY"

Which Model and Endpoint Should You Start With?

Use Flash while you are still deciding what the shot is, and when 720p and 20 seconds are enough. Use Kling 4.0 when you need 1080p, a clip longer than 20 seconds, a last frame or keyframes, reference audio, or video extend. Then pick the endpoint:

No source material yet: text-to-video.
You have a key frame or a starting image: image-to-video.
You need a subject, style or sound to carry across a shot: reference-to-video.
You have a clip that is right except for one thing: video-edit.
You need a longer shot that continues an existing one: video-extend (Kling 4.0 only).

In our test of Kling 4.0 video-edit, a 5 second coastal-road clip of a red vintage convertible was edited with a prompt to turn it into a snowy winter evening while keeping the car and its motion. The result kept the same car, driver and motion, with snow on the road and cliffs, at 1280x720 with the audio kept. In our test of Kling 4.0 video-extend, a 5 second sailboat-at-sunrise clip was continued by 5 seconds. The boat and bay carried on and the camera rose to reveal a harbor, producing a 10 second clip with audio. These are two quick tests, not a benchmark.

How Do You Evaluate a Video Model Fairly?

This is a method, not a set of results. It works for Kling 4.0, Kling 3.0 or any other video model.

Pick one repeatable scene. For example: a five-second, 16:9, 720p shot of a red ceramic mug on a wooden table, where one hand enters from the right, lifts the mug once, and the camera makes a slow push-in.
Lock the inputs. Fix the prompt, input image if used, duration, aspect ratio, resolution and output count. If a setting cannot be matched between two models, mark that row incomparable.
Score against written checks. For the mug scene: correct mug color, correct table, hand enters from the right, one lift, slow push-in, and no extra subject. Record which instruction failed, not just that a clip looked bad.
Compute the usable-output rate. This is the number of clips passing every check divided by completed clips. Keep failed jobs, reruns, cost and review time in separate fields.
Repeat. One good clip says little. Run the same inputs several times and look at how many survive review.

FAQ

Is Kling 4.0 Flash available on WaveSpeedAI?

Yes. Kling 4.0 Flash is live with four endpoints: text-to-video, image-to-video, reference-to-video and video-edit. Kling 4.0 is live with those four plus video-extend.

What is the difference between Kling 4.0 Flash and Kling 4.0?

Flash is the fast, lower-cost tier: 720p, clips of 3 to 20 seconds, first-frame image-to-video, and image and video references. Kling 4.0 adds 1080p, clips up to 30 seconds, last frame and keyframes, reference audio and video extend.

How are they priced on WaveSpeedAI?

Per second of generated video, with no subscription. At the time of writing, Flash text-to-video and image-to-video cost $0.094/s, and Kling 4.0 costs $0.157/s at 720p and $0.235/s at 1080p. See the pricing section above and the Kling 4.0 API page for current prices.

Do I need a Kling subscription to use Flash on WaveSpeedAI?

No. Any WaveSpeedAI account can use Flash and Kling 4.0, through the API or the browser Video Generator. The Ultra Yearly requirement applied to Flash early access on Kling’s own platform.

How long can a clip be, and at what resolution?

Flash clips run 3 to 20 seconds at 720p. Kling 4.0 clips run 3 to 30 seconds at 720p or 1080p. Both generate synchronized audio. There is no 4K tier on these endpoints. Kling 3.0 and Kling O3 have native 4K tiers.

Where do I find the model pages and the API?

The Kling 4.0 API page links to everything. Requests go to https://api.wavespeed.ai/api/v3/<model id>, for example kwaivgi/kling-v4.0-flash/text-to-video or kwaivgi/kling-v4.0/text-to-video.

Prices and specifications may change. Recheck the model pages and Kling’s own announcements before committing production work.

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