Kling 4.0 Vertical Video: 9:16, 1:1 and 21:9 Tested

TL;DR

• Kling 4.0 text-to-video supports four aspect ratios: 16:9, 9:16, 1:1 and 21:9. For vertical video, set aspect_ratio to 9:16. You don't need the word "vertical" in the prompt.
• Measured 720p output sizes: 16:9 is 1280×720, 9:16 is 720×1280, 1:1 is 940×940, 21:9 is 1460×624. Each ratio is composed for its frame, not cropped from a landscape clip.
• Aspect ratio doesn't change the price: a 5-second 720p clip is $1.10 in any ratio. Image-to-video follows the first frame's ratio, so upload a vertical image to get a vertical clip.

Output sizes for each aspect ratio

aspect_ratio	Measured 720p size	Good for
16:9 (text-to-video default)	1280×720	Landscape video, web hero, YouTube
9:16	720×1280	TikTok, Reels, YouTube Shorts
1:1	940×940	Feed ads, product listing video
21:9	1460×624	Cinematic banners, website headers

Measured on 720p, 5-second clips at $1.10 each, October 2026. We did not measure 1080p sizes.

Kling 3.0 offers 16:9, 9:16 and 1:1 only, with no 21:9.

Same prompt, 16:9 vs 9:16

These two clips use the same prompt. Only aspect_ratio changed.

Product shot of a glass perfume bottle on wet black stone, a single drop of water falls and splashes beside it, slow orbit around the bottle, soft studio rim light, crisp water drip sound

16:9, 1280×720	9:16, 720×1280

Generate with this prompt → (set the aspect ratio to 9:16 on the model page)

The landscape clip shows a wide, squat bottle with black space on both sides. The vertical clip switches to a tall, slim bottle, with the stone and water in the lower half. Kling 4.0 re-composes the subject for the frame, down to the bottle's proportions. If the product must look identical, use image-to-video with your product photo as the first frame. Both clips are 720p, 5 seconds, $1.10 each; the vertical one took 187 seconds from submit to done.

9:16 vertical: lake pier

A calm lake at sunrise, mist drifting over the water, a wooden pier in the foreground, soft golden light

Generate with this prompt → (choose 9:16)

kling-4.0/text-to-video, 9:16, 720×1280, 5 seconds, $1.10.

Vertical frames suit scenes with depth. The pier runs from the bottom edge toward the sun on the horizon and fills the tall frame.

1:1 square: pine canopy

A quiet forest clearing with tall pine trees, sunlight filtering through the branches, a gentle breeze

Generate with this prompt → (choose 1:1)

kling-4.0/text-to-video, 1:1, 940×940, 5 seconds, $1.10.

The prompt names no camera angle, and the model chose a low shot looking up into the canopy, with branches closing in from all four sides. At 940 pixels, the square's side is longer than the 720p short edge.

21:9 ultrawide: mountain valley

A wide mountain valley at dawn, layers of ridges fading into haze, a slow river winding through the valley floor

Generate with this prompt → (choose 21:9)

kling-4.0/text-to-video, 21:9, 1460×624, 5 seconds, $1.10.

21:9 suits landscapes that spread sideways. The ridges and the river run across the frame from edge to edge.

Vertical video through the API

Set aspect_ratio to 9:16 in the request:

curl -X POST https://api.hiapi.ai/v1/tasks \
  -H "Authorization: Bearer $HIAPI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "kling-4.0/text-to-video",
    "input": {
      "prompt": "A calm lake at sunrise, mist drifting over the water, a wooden pier in the foreground, soft golden light",
      "resolution": "720p",
      "duration": 5,
      "aspect_ratio": "9:16"
    }
  }'

• aspect_ratio accepts 16:9, 9:16, 1:1 and 21:9. Leave it out and you get 16:9.
• The response returns data.taskId; poll GET /v1/tasks/<taskId> for the result. The four 9:16, 1:1 and 21:9 clips in this article each finished in 186–194 seconds.
• Full request, callback and Python examples are in the Kling 4.0 API guide.

Image-to-video follows the first frame

kling-4.0/image-to-video has no default aspect_ratio; leave it out and the clip follows the first frame's ratio. In our test, a 1280×720 first frame produced a 1280×720 clip.

For vertical output, upload a vertical first frame, such as a 720×1280 product photo. The first frame sets the composition, so the prompt only needs motion, camera and sound. See the Kling 4.0 image-to-video API guide for the request, and scene 6 of the Kling 4.0 prompt guide for prompt wording.

FAQ

Do I need "vertical" in the prompt?

No. The aspect_ratio parameter decides the frame. None of the 9:16, 1:1 or 21:9 prompts in this article mention a ratio.

Does vertical cost more?

No. Price depends only on resolution and seconds: $0.22/s at 720p and $0.33/s at 1080p, the same for all four ratios. See Kling 4.0 API pricing.

How long can a vertical clip be?

The same as landscape: any whole number from 3 to 30 seconds, with synchronized audio on every clip.

Is vertical cropped from a landscape clip?

No. With the same perfume prompt, the landscape clip has a wide bottle and the vertical clip has a tall one. The frame is generated for the ratio, not cut from the middle of a 16:9 clip.

Copy the perfume prompt above, set the ratio to 9:16 on the Kling 4.0 model page, and make your first vertical clip. New accounts get 200 free credits.