Amux

Extend video

Last updated September 13, 2026

Continue an existing video with a new segment using x-ai/grok-imagine-video. This capability is unique to this model.

Continue an existing video with a newly generated segment using x-ai/grok-imagine-video, in the native xAI request shape.

POSThttps://gateway.amux.ai/v1/videos/extensions

Authorization

header
AuthorizationstringRequired

Bearer <your Amux key> An API key issued by this site.

Request

application/json
modelstringRequired

Fixed to x-ai/grok-imagine-video.

promptstringRequired

Required: describes what happens in the continuation.

videoobjectRequired

The source video to extend; its length must be between 2 and 15 seconds.

›videoobject
urlstring

Source video address (mp4); must be a publicly reachable URL.

durationintegerDefault 6

Length of the added segment in seconds, 2-10, defaulting to 6. The total length is the source length plus this value.

Response

200response

The task was created.

400response

Invalid request (missing prompt or source video, source length out of range, or duration outside 2-10).

402response

Insufficient balance to reserve the cost of this task.

This capability is unique to this model

x-ai/grok-imagine-video-1.5 does not support extension. This is a capability difference of the model itself: the generation endpoint does not accept a video field either, so editing and extension cannot be performed through it. Use x-ai/grok-imagine-video when these capabilities are required.

🔴 duration is the length of the added segment, not the total

A 3-second source with duration: 2 yields a 5-second result.

⚠️ video.duration in the response likewise reports the added segment (2 in that example), not the total length. To obtain the total, add the source length to duration.

Billing also counts the added segment, matching the upstream's own basis.

Value domains

Source video length2–15 seconds; shorter input is rejected upstream
duration2–10 seconds, defaulting to 6

Billing

cost = added segment seconds × resolution tier rate
     + source video seconds × input-video per-second rate

The source segment is not charged again as output — it is counted once at the input-video rate.

Official price reference

The figures below are xAI's public list prices, provided for order-of-magnitude estimation. They are not this site's charges — the authoritative rates are on the model detail and pricing pages.

TierOutput (per second)Input video (per second)
480p$0.05$0.01
720p$0.07$0.01

On that basis, extending a 3-second 480p video by 2 seconds is roughly 2 × 0.05 + 3 × 0.01 = 0.13.

Retrieval

The returned request_id is the Amux task id; retrieval works exactly as for generation tasks, via the xAI shape or the unified shape.

cURL
curl https://gateway.amux.ai/v1/videos/extensions \
  -H "Authorization: Bearer $AMUX_API_KEY" \
  -d '{
    "model": "x-ai/grok-imagine-video",
    "prompt": "The boat drifts further into the distance",
    "duration": 5,
    "video": {
      "url": "https://…/source.mp4"
    }
  }'
{
  "request_id": "<string>"
}