Kling 4.0 API

About Kling 4.0

The extension workflow accepts video_url up to 60 seconds long. It extracts the final frame, generates a new segment through image-to-video and joins that segment to the original clip.

Call it with the model name kling/4.0/video-extend on POST /jobs/createTask, from $0.942.

Introduction

Kling 4.0 Video extend carries on a clip you already have. Send a video of up to 60 seconds and, if you like, a prompt for what happens next. The last frame of your clip becomes the opening frame of a new segment of 3 to 30 seconds, made with Kling 4.0 image-to-video. You get back one MP4 with your original and the new segment joined, and the new segment on its own as well.

Choose a Kling 4.0 mode by starting material

Key features

The last frame sets the scene

The new segment starts on your final frame, so the people, the set and the light carry over. Motion does not carry over the same way, because the model sees one still. Describe the movement you want to continue.

Choose where it ends

Add last_image_url and the new segment finishes on that image. Leave it out and the model decides how the segment ends.

One file back, plus the new piece

The joined file keeps your clip's frame rate and framing, with no black bars. To line up the seam, the picture may be trimmed or adjusted by a few percent at the edges, and the sound crossfades at the seam. Your clip keeps its own sound, and the new segment always has generated stereo sound.

The shape follows your clip

There is no aspect ratio setting. The new segment follows the shape of your source.

Request parameters

Pricing

Prices are in USD. The API uses a separate USD balance. Website credits cannot be used or transferred to it, and API funds cannot be transferred to website credits. When a task is accepted, we reserve the maximum quoted amount from your API balance. On completion, we charge for actual usage, never more than the hold, and release the remainder. If the task fails, the hold is released.

Send the same request body to POST /jobs/quote to see the estimated and maximum USD charge before running. A quote does not run the task or charge your balance.

Use cases

Finish a shot that ended too early

A walk that stops before the door, a camera move that cuts out mid-way: extend it by a few seconds and describe only what is left to happen.

Build a longer scene step by step

Extend a clip, then extend the joined result again.

Land on a planned final image

Give a closing frame and the clip arrives at the composition you need, such as a product back at its main angle.

Prompt guide & pro tips

Describe the next beat, not the whole scene

The frame already shows who and where. Spend the prompt on the action that follows, the camera and the sound. With no prompt, the model carries the scene on by itself.

End your source on a clean frame

The last frame is all the model sees. A blurred or half-cut ending carries straight into the new segment, so trim your clip to a sharp frame first.

Match the resolution

Pick the same resolution as your source so the seam does not show a step in sharpness. Draft with a short segment, then ask for the longer one.

API quick start

Call the Kling 4.0 API in three steps

1. Create an API key. Sign in to PopNow and create a key in the API console. Keys start with sk-popnow-. API calls use your separate USD balance.
2. Send the request. POST /jobs/createTask with model kling/4.0/video-extend and an input object that follows the parameter table. The response returns a task ID straight away.
3. Get the result. Poll GET /jobs/recordInfo with the task ID, or pass a callBackUrl and we post the result to it. Download the output links when the task succeeds.

# 1. Create the task. Keep the Idempotency-Key if you retry after a network error.
export IDEMPOTENCY_KEY="$(uuidgen)"
curl -X POST https://api.popnow.ai/api/v1/jobs/createTask \
  -H "Authorization: Bearer $POPNOW_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: $IDEMPOTENCY_KEY" \
  -d '{
  "model": "kling/4.0/video-extend",
  "input": {
    "video_url": "https://media.popnow.ai/effects/flower-bloom-1abd6efb.mp4",
    "resolution": "720p",
    "duration_seconds": 5
  }
}'

# 2. Copy data.taskId from the response, then poll until state is succeeded, failed, canceled or expired.
TASK_ID="TASK_ID_FROM_RESPONSE"
curl "https://api.popnow.ai/api/v1/jobs/recordInfo?taskId=$TASK_ID" \
  -H "Authorization: Bearer $POPNOW_API_KEY"

Replace the prompt and any links with your own. The API tab has the response, polling and callback reference.

About the Kling 4.0 Extend Video endpoint

duration_seconds is the added segment length, from 3 to 30 seconds. A prompt is optional, and last_image_url can define its ending. There is no aspect_ratio field: the continuation follows the source framing.

This workflow is not native whole-video continuation. Describe motion explicitly because generation begins from one still, and trim an unclear final frame before uploading. Billing covers the new segment, not the original footage.

Kling 4.0 API questions

More about Kling 4.0

Try it

Kling 4.0 AI Video Generator onlineCreate videos with Kling 4.0 in PopNow

Endpoints

All Kling 4.0 endpoints and pricing

Endpoints

Kling 4.0 · Create VideoKling 4.0 · Image to VideoKling 4.0 · Reference to VideoKling 4.0 · Edit Video

Docs

Kling 4.0 model ID and input schema in the API docsPopNow API quickstart: your first request in five minutesImage to video guide for the PopNow APIWebhooks: get Kling 4.0 results without polling