Runway Gen-4.5 vs Kling 2.5 Turbo

Q: Can I mix them in one project?

Yes. Same key, same endpoint; switch model shot by shot. Pricing is in Runway Gen-4.5 API pricing and Kling 2.5 Turbo API pricing; integration is in the Runway Gen-4.5 API guide. To compare for yourself, copy the rice-terrace prompt above and run it on the Runway Gen-4.5 model page.

TL;DR

For an 8-second option, or Runway's look, pick Runway Gen-4.5: $0.1715 per second, fixed 720p, no audio.
For 1080p, a last frame, 21:9, sound on text-to-video, or the lowest price, pick Kling 2.5 Turbo: $0.06 per second, $0.60 for 10 seconds.
Both are live on HiAPI: open the Runway Gen-4.5 model page to try it. New accounts get 200 free credits.

At a glance

	Runway Gen-4.5	Kling 2.5 Turbo
Per second	$0.1715	$0.06
10-second clip	$1.715	$0.60
Lengths	5 / 8 / 10 s (T2V at 9:16: 5 / 10)	5 / 10 s
Resolution	720p (16:9 is 1280×720)	~1080p (16:9 is 1920×1080)
Text-to-video aspect ratios	16:9, 9:16	16:9, 9:16, 1:1
Image-to-video input	One first frame, 5 ratios	First frame + optional last frame, 6 ratios (adds 21:9)
Audio	None	T2V always on; I2V none
Prompt limit	1,000 characters	2,500 characters, plus `negative_prompt`

Same prompt, one clip from each

Text-to-video: rice terraces at sunrise

Both at 16:9, 10 seconds, one run each. Resolution is each model's fixed output: 720p for Runway, about 1080p for Kling.

Aerial glide over a misty rice-terrace valley at sunrise, camera slowly rises to reveal distant mountains

Runway Gen-4.5:

Generate with Runway Gen-4.5 →

runway-gen-4.5/text-to-video, 16:9, 1280×720, 10 s, no audio, $1.715.

Kling 2.5 Turbo:

Generate with Kling 2.5 Turbo →

kling-2.5-turbo/text-to-video, 16:9, 1920×1080, 10 s, with audio, $0.60.

What you can see:

Color: Runway goes for a warm orange sunrise with light reflecting off the flooded terraces; Kling's terraces are lush green, with a lens flare at the start.
The reveal: Kling starts close on the terraces and only shows the clouds and snowy peaks after it rises, so the reveal plays out fully. Runway has the mountains in frame from the first second; its change is the camera moving forward over the terraces.
Audio: the Kling clip has a track; Runway's doesn't.

Image-to-video: same first frame

The same 16:9 first frame, 10 seconds.

The scene slowly comes alive: clouds drift, light shifts across the mountain lake, gentle forward camera move

Runway Gen-4.5:

Generate with Runway Gen-4.5 →

runway-gen-4.5/image-to-video, 16:9, 1280×720, 10 s, no audio, $1.715.

Kling 2.5 Turbo:

Generate with Kling 2.5 Turbo →

kling-2.5-turbo/image-to-video, 16:9, 1920×1080, 10 s, no audio, $0.60.

What you can see:

Camera: Runway pushes forward clearly, and the rocky foreground slides out of frame over the 10 seconds. Kling's framing barely changes.
Motion in the scene: both move the clouds and shift the reflections; Kling's changes are subtler and stay closer to the source image.
Fit: for a "moving into the scene" feel, Runway's clip shows it more; for a loopable background where stability matters, Kling's fits better.

Which one for which job

The clip will sit in a 1080p slot (hero banner, landscape video): Kling 2.5 Turbo, 1920×1080 out.
Animatics and storyboards scored later: Runway Gen-4.5. Clips are silent anyway, and 8 seconds fits one full camera move.
Ending on a specific shot, or transitions: Kling 2.5 Turbo. Runway Gen-4.5 takes one first frame only.
21:9 ultrawide: Kling 2.5 Turbo image-to-video, 2200×940.
Volume work where unit price matters: Kling 2.5 Turbo, about a third of Runway's price for the same 10 seconds.

Switching cost

Both run on the same POST /v1/tasks with the same API key. Switching means changing model and input:

{"model": "runway-gen-4.5/image-to-video",
 "input": {"prompt": "...", "image_urls": ["https://your-cdn.example.com/frame.jpg"], "duration": 10, "aspect_ratio": "16:9"}}

{"model": "kling-2.5-turbo/image-to-video",
 "input": {"prompt": "...", "image_urls": ["https://your-cdn.example.com/frame.jpg"], "duration": 10, "aspect_ratio": "16:9"}}

Runway to Kling: change 8 seconds to 5 or 10; aspect ratios carry over. Kling to Runway: drop the second image, negative_prompt and cfg_scale, and keep the prompt under 1,000 characters.

FAQ

Runway Gen-4.5 costs almost 3× as much. What does the extra buy?

What we can verify: the 8-second option. The two models look different, so judge from the same-prompt clips above. On resolution and sound, Kling 2.5 Turbo is ahead.