Kling 4.0 - Unifically

Generate high-quality AI videos using Kling 4.0, Kuaishou’s flagship model. Supports text-to-video, up to 10 raw reference images, persistent subject/object elements, keyframes (start, up to 8 middle frames, end), video transform, video reference, and multi-shot generation. Clips run 3–30 seconds with native stereo audio on by default, a new 21:9 ultrawide ratio, and prompts up to 8,000 tokens. More on this model: Kling 4.0 API page.

Model

kuaishou/kling-4.0-video

Parameters

Parameter	Type	Required	Default	Description
`video_mode`	string	No	-	Input mode. Allowed: `"elements"`, `"start_end_frame"`, `"transform"`, `"video_reference"`. Omit for text-to-video
`prompt`	string	Conditional	-	Text prompt (up to 8,000 tokens). Use `@Image1`, `@Element1` to reference inputs. Mutually exclusive with `multi_shots`
`mode`	string	No	`"std"`	`"std"` (720p) or `"pro"` (1080p); see Pricing. 4K is not available yet and is rejected
`duration`	integer	No	`3`	Video length in seconds (3–30). Ignored when `video_url` is set (the source video’s length is used)
`aspect_ratio`	string	No	-	`"auto"`, `"1:1"`, `"9:16"`, `"16:9"`, or `"21:9"`. Must be `"auto"` when `video_url` is set. Omit to let the server choose (`"auto"` if `video_url` or `start_end_frame`, else `"16:9"`)
`native_audio`	boolean	No	`true`	Generate AI audio (two-channel stereo). On by default for 4.0
`keep_audio`	boolean	No	`true`	Preserve original audio from the source video (`transform` / `video_reference` modes)
`image_urls`	string[]	No	-	Raw reference image URLs uploaded per request (max 10). No description, no reuse. Use `@Image1`, `@Image2` in `prompt`
`start_image_index`	integer	No	-	1-based index into `image_urls` marking which reference image anchors the first frame. No end-frame equivalent
`elements`	ElementInput30[]	No	-	Persistent subject/object assets (max 7, of which at most 3 `type: "video"`). Auto-created on Kling and auto-deleted if submit fails. Use `@Element1`, `@Element2` in `prompt`. Coexists with `image_urls`
`start_frame_url`	string	No	-	First frame image URL (`start_end_frame` mode)
`keyframe_urls`	string[]	No	-	Middle keyframe image URLs, in order, between `start_frame_url` and `end_frame_url` (`start_end_frame` mode, max 8). 4.0 only
`end_frame_url`	string	No	-	Last frame image URL (`start_end_frame` mode)
`video_url`	string	No	-	Source video URL (`transform` / `video_reference` modes). Billed per second of the source video at the with-video rate
`multi_shots`	array	No	-	Multi-shot sequence (2–6 shots, each with `prompt` and `duration`, total 3–30 s). Mutually exclusive with `prompt`. Not available in `start_end_frame` mode
`nsfw_check`	boolean	No	`true`	Check uploaded media inputs for NSFW content

Modes

Mode	Required inputs	Optional inputs	Notes
omitted (text-to-video)	`prompt` or `multi_shots`	—	Rejects every input field including `elements`, `image_urls`, `start_frame_url`, `video_url`
`elements`	At least one of `image_urls`, `elements`	—	Combined `image_urls` + `elements` cap of 15 (`image_urls` ≤ 10, `elements` ≤ 7). `video_url` rejected
`start_end_frame`	`start_frame_url`	`keyframe_urls`, `end_frame_url`	Keyframes mode. At most 10 frames in total (start + middle + end). `aspect_ratio` is ignored (the frames set it). `elements` and `multi_shots` rejected
`transform`	`video_url`	`image_urls`, `elements`	Combined `image_urls` + `elements` cap of 14 (the source video is the 15th reference). `aspect_ratio` must be `"auto"`. Source video short side must be at least 700 px
`video_reference`	`video_url`	`image_urls`, `elements`	Combined `image_urls` + `elements` cap of 14. `aspect_ratio` must be `"auto"`

Text-to-video with elements — set video_mode: "elements" and pass only the elements array (no image_urls required). The omit-video_mode path is strictly for pure text-to-video with zero inputs; any reference (image or element) requires elements mode.

Not available yet on Kling 4.0 — 4K output, 10-bit HDR, video extension, voice references, multi-clip video editing, and Kling 4.0 Flash. Requests for mode: "4k" are rejected.

Pricing

Billed per second of output video. With a source video (transform / video_reference modes) the with-video rate applies, billed per second of the input video.

Mode	Resolution	Per second	With source video
`std`	720p	$0.141	$0.169
`pro`	1080p	$0.212	$0.254

A 10% launch sale applies to all four rates until 2026-10-29 01:00 UTC.

Reference images vs elements

image_urls — raw images uploaded per request. Single-use, no description, no reuse across tasks. Cap 10. Reference in prompt as @Image1, @Image2, …
elements — persistent subject/object assets stored on the Kling account. Auto-created from your input on submit and auto-deleted if the submit fails. Cap 7, at most 3 video-based. Reference in prompt as @Element1, @Element2, …

Both can be used together; they share the per-mode combined cap (15 in elements mode, 14 plus the source video in transform / video_reference).

Elements

Kling 4.0 supports both IMAGE and VIDEO elements. Unlike 3.0 Omni, a video-type element may be combined with video_url; at most 5 video inputs in total (video_url plus video-type elements).

"elements": [
  {"description": "Woman in red jacket", "type": "image", "image_urls": ["front.jpg", "side.jpg"]},
  {"description": "Man dancing", "type": "video", "video_url": "dance.mp4"}
]

Each element accepts:

Parameter	Type	Default	Description
`description`	string	`""`	Short description of the element (max 100 chars)
`type`	string	`"image"`	Element source type: `"image"` or `"video"`
`image_urls`	string[]	-	Source image URLs for an image element (max 4)
`video_url`	string	-	Source video URL for a video element
`nsfw_check`	boolean	No	Check uploaded media inputs for NSFW content. Default: `true`

Example - Text-to-Video

curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "kuaishou/kling-4.0-video",
    "input": {
      "prompt": "A majestic eagle soaring through mountain peaks at sunset",
      "duration": 10,
      "mode": "pro",
      "aspect_ratio": "21:9"
    }
  }'

Example - With Elements

curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "kuaishou/kling-4.0-video",
    "input": {
      "video_mode": "elements",
      "prompt": "@Element1 walks through a park at sunset",
      "elements": [
        {"description": "Woman in red jacket", "type": "image", "image_urls": ["https://example.com/front.jpg"]}
      ],
      "duration": 10,
      "mode": "pro"
    }
  }'

Example - Reference Images with Start Frame

curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "kuaishou/kling-4.0-video",
    "input": {
      "video_mode": "elements",
      "prompt": "@Image2 walks toward @Image1 across a meadow",
      "image_urls": [
        "https://example.com/character.jpg",
        "https://example.com/scene.jpg"
      ],
      "start_image_index": 2,
      "duration": 5,
      "mode": "pro"
    }
  }'

Example - Keyframes

curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "kuaishou/kling-4.0-video",
    "input": {
      "video_mode": "start_end_frame",
      "prompt": "A seed sprouts, grows into a sapling, and blooms",
      "start_frame_url": "https://example.com/seed.jpg",
      "keyframe_urls": [
        "https://example.com/sprout.jpg",
        "https://example.com/sapling.jpg"
      ],
      "end_frame_url": "https://example.com/bloom.jpg",
      "duration": 15,
      "mode": "pro"
    }
  }'

Example - Transform

curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "kuaishou/kling-4.0-video",
    "input": {
      "video_mode": "transform",
      "prompt": "Restyle the video as stop-motion claymation",
      "video_url": "https://example.com/source.mp4",
      "mode": "pro"
    }
  }'

Example - Multi-Shot

curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "kuaishou/kling-4.0-video",
    "input": {
      "mode": "pro",
      "multi_shots": [
        { "prompt": "Wide shot of city skyline", "duration": 10 },
        { "prompt": "Close-up of glass buildings", "duration": 10 }
      ]
    }
  }'

Response

{
  "code": 200,
  "success": true,
  "data": {
    "task_id": "abc123def456",
    "status": "processing"
  }
}

Volume discounts are available for almost all models. Reach out at contact@unifically.com to discuss custom pricing.

​Model

​Parameters

​Modes

​Pricing

​Reference images vs elements

​Elements

​Example - Text-to-Video

​Example - With Elements

​Example - Reference Images with Start Frame

​Example - Keyframes

​Example - Transform

​Example - Multi-Shot

​Response

Model

Parameters

Modes

Pricing

Reference images vs elements

Elements

Example - Text-to-Video

Example - With Elements

Example - Reference Images with Start Frame

Example - Keyframes

Example - Transform

Example - Multi-Shot

Response