FLUX 3 API

About FLUX 3

FLUX 3 video extend is native: send the clip as video_url with a prompt for what happens next, and the model continues the same shot without a cut.

Call it with the model name black-forest-labs/flux-3/video-extend on POST /jobs/createTask, from 90 credits for a 5-second clip ($0.90). New accounts get 30 free credits to try it in the Playground first.

Introduction

FLUX 3 Video extend continues a clip you already have. It takes an MP4 of up to 15 seconds, starts from its last frame and generates 5 to 20 new seconds with synchronized sound. The result is the new segment only; your source is not included.

Choose a mode by starting material

Key features

Picks up from the last frame

The new segment begins where your clip ended, with the same person, place and light. In our test it opened with a short dissolve before the next action began.

New segment only

You receive just the added seconds, so the final cut is assembled in your editor with the original clip.

Request parameters

Pricing

Prices are in credits, the same credits you use on the website (1 credit = $0.01). The hold is taken when the task is accepted and settled to the actual charge when it finishes; failed tasks are refunded.

For an exact number before you run, send the same body to POST /jobs/quote.

Use cases

Lengthening a good clip

Take a six-second shot you like and carry the scene on.

Building sequences

Chain several extensions, each with one clear action.

Fixing an ending

Keep a strong first half and write a new continuation.

Prompt guide & pro tips

Write the next action

Describe what happens after the last frame, not what the clip already shows. In our tests, asking for a pull-back or a new angle cut to a different shot partway through; keeping the camera on the same framing gave one continuous take.

Move in small steps

The model can skip an in-between move, such as walking to a new spot, so ask for the destination action directly.

Expect a short blend at the start

The first fraction of a second can show a dissolve with some ghosting; trim it in the edit if it bothers you.

Match the shape

Leave the aspect ratio out to keep the source shape.

Check the sound

Add a Sound: line so the new segment matches the old.

API quick start

Call the FLUX 3 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- and use the same credits as the website.
2. Send the request. POST /jobs/createTask with model black-forest-labs/flux-3/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": "black-forest-labs/flux-3/video-extend",
  "input": {
    "prompt": "A slow aerial shot drifting over a misty pine forest at sunrise",
    "video_url": "https://media.popnow.ai/effects/flower-bloom-1abd6efb.mp4",
    "quality": "standard",
    "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 FLUX 3 Extend Video endpoint

The response contains the full clip, original first and extension after, with sound carried through.

New seconds are billed at twice the text to video rate.

Required fields are video_url and prompt; aspect_ratio, duration_seconds, resolution, quality and generate_audio mirror text to video.

Use quality draft to preview the continuation cheaply before paying the standard rate.

Keep the extension prompt about the next beat only, such as a hand moving or a head turning, so the seam between source and new footage stays invisible.

FLUX 3 API questions

More about FLUX 3

Try it

FLUX 3 AI Video Generator onlineCreate videos with FLUX 3 in PopNow

Endpoints

All FLUX 3 endpoints and pricing

Endpoints

FLUX 3 · Create VideoFLUX 3 · Image to VideoFLUX 3 · Upscale Video

Docs

FLUX 3 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 FLUX 3 results without polling