Kling 4.0

Kling 4.0 is Kuaishou's video model announced in September 2026. One model ID covers five modes: text to video, image to video with up to 10 frames, reference-based generation from images, videos and audio, video editing, and video extension. Every clip is 3–30 seconds at 720p or 1080p with stereo sound. Send the request, keep the returned task ID, and read the finished video from the task. Media goes in as URLs.

Model IDs

See the model page for current prices.

Quick example

curl https://api.seedrouter.ai/v1/videos/generations \
  -H "Authorization: Bearer $SEEDROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "kling-4-0",
    "prompt": "A woman with a red umbrella walks down a neon-lit street on a rainy night, signs shimmering in the puddles, the camera tracking low beside her. No text, no logos.",
    "resolution": "720p",
    "duration": 5,
    "aspect_ratio": "16:9"
  }'

Endpoint

POST https://api.seedrouter.ai/v1/videos/generations

The response is a task ({"id": "task_...", "status": "processing"}), not the finished video. Poll GET /v1/tasks/{task_id} for the result. Keep API keys in server-side code.

Parameters

Every clip comes with stereo sound; there is no sound switch. There is no mode, negative_prompt, watermark or multi-shot field. The schema is strict: unknown fields are rejected rather than ignored. callback_url is not available; poll the task instead.

Modes

The mode follows the media you send and omni_reference_task_type:

Frames and reference media cannot be mixed in one request. Next to reference videos or audio, image_urls count as reference images only with omni_reference_task_type: "reference"; use reference_image roles otherwise. A video_url without edit or extend is rejected.

Keyframes

{
  "model": "kling-4-0",
  "prompt": "A girl walks from the window to the door, then looks back and smiles",
  "image_with_roles": [
    {"url": "https://example.com/1.png", "role": "first_frame"},
    {"url": "https://example.com/2.png", "role": "keyframe"},
    {"url": "https://example.com/3.png", "role": "last_frame"}
  ],
  "duration": 10
}

Reference

{
  "model": "kling-4-0",
  "prompt": "The woman from @Image1 walks along the beach with the camera movement of @Video1",
  "image_with_roles": [{"url": "https://example.com/woman.png", "role": "reference_image"}],
  "video_urls": ["https://example.com/camera.mp4"],
  "aspect_ratio": "auto",
  "duration": 5
}

Edit

{
  "model": "kling-4-0",
  "prompt": "Change the scene to a snowy winter evening",
  "omni_reference_task_type": "edit",
  "video_url": "https://example.com/in.mp4"
}

The input video must be at least 3 seconds; only its first 30 seconds are used. Without duration, the output follows the input video.

Extend

{
  "model": "kling-4-0",
  "prompt": "The camera keeps moving forward as the sky grows darker",
  "omni_reference_task_type": "extend",
  "video_url": "https://example.com/in.mp4",
  "duration": 5
}

Extension continues from the input video's last frame and returns the original plus the new part. Add last_frame_image to choose where it ends.

Media inputs

Images, videos and audio are public HTTP(S) URLs. Base64 data URIs are not accepted: upload the files to your own storage and pass their URLs. Images, videos and audio together are at most 15 reference files.

Pricing dimensions

Check the model pricing section for current rates. Kling 4.0 is billed per second of video, at a rate set by the resolution:

text, image, reference without videos:  cost = duration × standard rate
extend:                                 cost = new seconds × standard rate
edit, reference with videos:            cost = (output + max(output, input)) × video-input rate

input is the summed length of the input videos, rounded up to whole seconds and capped at 30. It is measured when the request is accepted, so the amount reserved is the amount charged. A video whose length cannot be read is rejected before anything is charged. Example: editing a 5.2-second video into a 3-second result bills 3 + 6 = 9 seconds. Failed tasks are not charged.

Output schema

Submission returns the task:

{"id": "task_...", "model": "kling-4-0", "status": "processing", "created_at": 1789689600}

Get the task

GET https://api.seedrouter.ai/v1/tasks/{task_id}

Poll every 10–20 seconds until status is completed or failed. A network timeout while polling does not mean generation failed: keep the task ID and resume checking it. Do not create another task to check progress.

Completed task

{
  "id": "task_...",
  "model": "kling-4-0",
  "status": "completed",
  "created_at": 1789689600,
  "finished_at": 1789689800,
  "output": {
    "video_url": "https://static.seedrouter.ai/media/tasks/task_example/0.mp4"
  }
}

In our tests 3-second 720p clips came back as MP4 (H.264) at 1280 × 720 with a stereo AAC track, 2 min 41 s to 4 min 22 s after submission. An extended 5.2-second video came back 8.1 seconds long.

Errors

Requests rejected before a task is created return an HTTP error with an error object and are not charged. A task that fails after acceptance returns HTTP 200 when queried, with status: "failed" and an error object.

See the shared error catalog for codes, HTTP statuses, and retry guidance.

{
  "id": "task_...",
  "model": "kling-4-0",
  "status": "failed",
  "error": {
    "code": 60001,
    "message": "The request was rejected by the content policy. Please revise the prompt or input images."
  }
}

If submission itself times out, check your tasks before submitting again: the first request may have been accepted.

Tips

• Describe subject, place, camera move, light and sound; the clip's audio follows the prompt.
• Draft at 720p, then render the final shot at 1080p with the same request.
• Give longer clips keyframes so the scene moves where you want it.
• Add no text, no logos to keep invented marks out.

Related

• Kling 4.0 Playground and pricing
• Kling 3.0 API reference
• Download OpenAPI
• Copyable Markdown