Kling 4.0 - AnyFast

Use Kling 4.0 through AnyFast API to generate or edit videos from text prompts, keyframe images, and image or video references. Kling 4.0 uses a new interface: the model name is in the request path, output settings go in settings, and general options go in options.

Use the /kling/v2/.../kling-4.0 creation endpoints shown here. Do not include model or model_name in the request body. Do not mix in Kling Legacy parameters such as mode: "std", a top-level string duration, or multi_prompt.

Key capabilities

Text to video — Describe the scene, people, action, camera work, and sound in a prompt.
Image to video — Submit a prompt and first, middle, or last frame images in contents.
Omni reference generation — Combine prompts, reference images, and reference videos, then assign each asset a role in the prompt using its id.
Video editing — Use the Omni reference endpoint with a base_video and describe what to change and preserve.
Asynchronous task query — Query status and results using the system task ID from the create response.

Capability	Creation endpoint	Main input
Text to video	`POST /kling/v2/text-to-video/kling-4.0`	`prompt`
Image to video	`POST /kling/v2/image-to-video/kling-4.0`	Prompt and keyframe images in `contents`
Omni reference generation	`POST /kling/v2/omni-video/kling-4.0`	Prompt, reference images, and reference videos
Video editing	`POST /kling/v2/omni-video/kling-4.0`	Prompt and `base_video`

Base URL and authentication

Use https://www.anyfast.ai as the base URL. Include these request headers:

Authorization: Bearer YOUR_ANYFAST_API_KEY
Content-Type: application/json

Replace YOUR_ANYFAST_API_KEY with an AnyFast API key that has access to this model.

Quick examples

curl --request POST \
  --url 'https://www.anyfast.ai/kling/v2/text-to-video/kling-4.0' \
  --header 'Authorization: Bearer YOUR_ANYFAST_API_KEY' \
  --header 'Content-Type: application/json' \
  --data '{
    "prompt": "A red car drives slowly along a rain-soaked street as the camera pans right. Realistic style, natural rain sound, no subtitles, and no sudden cuts.",
    "settings": {
      "resolution": "720p",
      "aspect_ratio": "21:9",
      "duration": 3
    },
    "options": {
      "watermark_info": {
        "enabled": false
      }
    }
  }'

curl --request POST \
  --url 'https://www.anyfast.ai/kling/v2/image-to-video/kling-4.0' \
  --header 'Authorization: Bearer YOUR_ANYFAST_API_KEY' \
  --header 'Content-Type: application/json' \
  --data '{
    "contents": [
      {
        "type": "prompt",
        "text": "Start from @start and preserve the person's identity and composition. The person smiles and raises a hand as a breeze moves their hair. Add natural wind sound. Use one continuous shot, no subtitles."
      },
      {
        "type": "first_frame",
        "url": "https://example.com/first-frame.jpg",
        "id": "start"
      }
    ],
    "settings": {
      "resolution": "720p",
      "duration": 3
    },
    "options": {
      "watermark_info": {
        "enabled": false
      }
    }
  }'

curl --request POST \
  --url 'https://www.anyfast.ai/kling/v2/omni-video/kling-4.0' \
  --header 'Authorization: Bearer YOUR_ANYFAST_API_KEY' \
  --header 'Content-Type: application/json' \
  --data '{
    "contents": [
      {
        "type": "prompt",
        "text": "Preserve the face, hairstyle, and clothes of the person in @actor. Use the action pacing from @motion. Show the person moving naturally in a bright training studio. Keep the camera steady and add no subtitles."
      },
      {
        "type": "refer_image",
        "url": "https://example.com/character.jpg",
        "id": "actor"
      },
      {
        "type": "feature_video",
        "url": "https://example.com/motion.mp4",
        "id": "motion"
      }
    ],
    "settings": {
      "resolution": "720p",
      "aspect_ratio": "1:1",
      "duration": 3
    },
    "options": {
      "watermark_info": {
        "enabled": false
      }
    }
  }'

curl --request POST \
  --url 'https://www.anyfast.ai/kling/v2/omni-video/kling-4.0' \
  --header 'Authorization: Bearer YOUR_ANYFAST_API_KEY' \
  --header 'Content-Type: application/json' \
  --data '{
    "contents": [
      {
        "type": "prompt",
        "text": "Edit @base: change only the red ceramic cup in the person's hand to blue. Preserve the person's face, clothes, hand movement, background, camera motion, dialogue, and ambient sound. Do not add objects or subtitles."
      },
      {
        "type": "base_video",
        "url": "https://example.com/source-video.mp4",
        "id": "base"
      }
    ],
    "settings": {
      "resolution": "720p",
      "aspect_ratio": "adaptive"
    },
    "options": {
      "watermark_info": {
        "enabled": false
      }
    }
  }'

Query task results

Video generation is asynchronous. A successful create response means the task was accepted, not that the video is ready. Save data.id from the create response and query it with the same AnyFast API key:

cURL

curl --request GET \
  --url 'https://www.anyfast.ai/kling/v2/tasks?task_ids=YOUR_TASK_ID' \
  --header 'Authorization: Bearer YOUR_ANYFAST_API_KEY'

The create response’s data is an object; the query response’s data is an array. Create response example:

{
  "code": 0,
  "message": "",
  "request_id": "REQUEST_ID",
  "data": {
    "id": "asyntask_EXAMPLE",
    "status": "submitted",
    "create_time": 1793672435967,
    "update_time": 1793672435967,
    "external_id": ""
  }
}

Field	Description
`code`	API business status code; the success example is `0`
`message`	API message
`request_id`	Request tracing identifier, when returned
`data.id`	System task ID; save it for querying
`data.status`	Current task status
`data.create_time`	Creation time as a Unix timestamp in milliseconds
`data.update_time`	Update time as a Unix timestamp in milliseconds
`data.external_id`	Caller-defined task identifier; may be empty if unset

Status	Meaning	Client action
`submitted`	Submitted	Keep querying
`processing`	Generating	Keep querying
`succeeded`	Complete	Read `outputs`
`failed`	Failed	Save the error and stop polling

We recommend querying every 10–20 seconds and setting an application-level wait limit. If the limit is reached, keep the task ID and query it later; do not immediately submit the same generation request again. Successful query response example:

{
  "code": 0,
  "message": "",
  "data": [
    {
      "id": "asyntask_EXAMPLE",
      "status": "succeeded",
      "create_time": 1793672435967,
      "update_time": 1793672563000,
      "outputs": [
        {
          "type": "video",
          "url": "https://example.com/generated-video.mp4",
          "duration": "3.042"
        }
      ]
    }
  ]
}

Select the output with type: "video" from the matching task’s outputs:

Field	Description
`url`	Video result URL
`duration`	Actual duration in seconds; may be a decimal string
`watermark_url`	Watermarked result URL, present only when provided

The query path does not include a model name or require an upstream task ID. Result URLs may expire or include access signatures. Download and save the video soon after generation; do not treat the URL as permanent storage.

Parameters

Create request

Parameter	Type	Required	Description
`prompt`	string	Required for text-to-video	Video description; can include both desired and unwanted content
`contents`	object[]	Used for image-to-video, Omni reference, and video editing	Prompt and keyframe or reference assets; must include a prompt item
`settings`	object	No	Output resolution, duration, and aspect ratio
`settings.resolution`	string	No	`720p` or `1080p`; explicit value recommended
`settings.duration`	integer	No	Integer from 3 to 30 seconds; explicit value recommended
`settings.aspect_ratio`	string	No	`21:9`, `16:9`, `9:16`, `1:1`, or `adaptive`
`options`	object	No	General options
`options.watermark_info.enabled`	boolean	No	Whether to additionally generate a watermarked version; defaults to `false`
`options.external_task_id`	string	No	Caller-defined task identifier; keep it unique within the current user scope
`options.callback_url`	string	No	Task-status callback URL defined by the official protocol; confirm support on the current channel before use

`contents` asset types

`contents[].type`	Purpose	Main fields
`prompt`	Describe generation or editing requirements	`text`
`first_frame`	First-frame image or constraint	`url`, `id`
`middle_frame`	Middle keyframe or constraint	`url`, `id`
`last_frame`	Last-frame image or constraint	`url`, `id`
`refer_image`	Reference image for appearance, scene, or style	`url`, `id`
`feature_video`	Reference video for motion or other features	`url`, `id`
`base_video`	Source video to edit	`url`, `id`

Asset IDs must be unique within a task. Assign separate unique IDs to multiple middle_frame or refer_image items. The official protocol also defines element and voice asset types for referencing created characters and voices. These require the corresponding assets and management capabilities, so this page does not include asset-management examples.

Output and input limits

Output settings

When settings.aspect_ratio is specified, the output uses that ratio. With adaptive or when the field is omitted, the system first checks the prompt for an aspect-ratio request, then uses the edited video, keyframes, or other input videos to determine the ratio. If none applies, it uses 16:9. For text-to-video, an explicit settings.duration takes precedence. If omitted, the system checks the prompt for a duration request and defaults to 10 seconds when none is clear. For the Omni reference endpoint, duration is determined in this order:

Explicit settings.duration.
A clear duration request in the prompt.
The duration of base_video.
A default of 10 seconds if none of the above is available.

Submit at most one base_video to the Omni reference endpoint. The video-editing example omits settings.duration; set it to control the output length explicitly.

Input asset requirements

The following are official parameter constraints; actual availability can also depend on the connected resources.

Asset	Requirement
Image formats	JPG, JPEG, PNG
Image size	Up to 30 MB each
Image dimensions	At least 300 px wide and 300 px high
Image aspect ratio	2:5–5:2
Number of images	Up to 10
Video formats	MP4, MOV
Video size	Up to 300 MB each
Video duration	Each video and the total input-video duration must be 3–30 seconds
Video dimensions	700–4553 px wide and high; up to 8,294,400 total pixels
Video aspect ratio	2:5–5:2
Input frame rate	24–60 fps
Output frame rate	24 fps

Images can be submitted by URL or supported Base64 content. Videos use URLs. The server must be able to access each URL directly and retrieve the asset file. The Omni reference endpoint also has these limits:

Images, videos, elements, and voices combined: up to 15 assets.
With no video-character elements, up to 5 reference videos.
With video-character elements, the combined number of video-character elements and reference videos must not exceed 5.
Total input-video duration includes feature reference videos, the video being edited, and video-character elements.

Prompt length

These limits apply to the text-to-video prompt or the prompt item’s text in contents:

Text	Limit
English only	26,000 characters
Non-English only	11,000 characters
Mixed text	English characters ÷ 26,000 + non-English characters ÷ 11,000 ≤ 1

Prompting tips

Describe the following in order:

Subject and setting → action sequence → camera movement → sound requirements → things to avoid

You can describe multiple shots directly in the prompt. Prompts state the intended result; exact action timing and shot cuts are not guaranteed. We recommend explicitly setting settings.duration to control output length and cost.

General options

external_task_id does not replace the system task ID or guarantee duplicate-charge prevention.
This guide uses data.id from the create response to query tasks; callbacks and external-ID queries are not required.

API Reference

View Kling 4.0 request and response fields for each capability.

​Key capabilities

​Base URL and authentication

​Quick examples

​Query task results

​Parameters

​Create request

​contents asset types

​Output and input limits

​Output settings

​Input asset requirements

​Prompt length

​Prompting tips

​General options

API Reference

Key capabilities

Base URL and authentication

Quick examples

Query task results

Parameters

Create request

`contents` asset types

Output and input limits

Output settings

Input asset requirements

Prompt length

Prompting tips

General options