Grok Imagine 1.5 Fast Video Extend API: Extend xAI Clips

Mis à jour 18 oct. 2026

What is Grok Imagine 1.5 Fast Video Extend?

Grok Imagine 1.5 Fast Video Extend continues a video Grok Imagine 1.5 Fast Video already generated, on the same 1.5 engine. You pass the task_id of the finished generation and choose how the continuation is driven: a preset, or your own prompt and timing.

It is the companion to the speed-optimized Grok Imagine Video route — the way to get past that model's 10-second ceiling by chaining continuations onto a video you like.

Key features of Grok Imagine 1.5 Fast Video Extend

Two mutually exclusive modes

Send video_preset for preset mode, where the preset drives the style. Omit it for custom mode, where prompt, extend_at, and extend_duration are all required.

Branch from any second

extend_at takes a decimal second in the source video, so a continuation can pick up before the final frame rather than only after it.

Past the 30-second ceiling

Grok Imagine Video caps a single pass at 30 seconds. Chaining 6 or 10-second extensions is how a sequence runs longer.

What Grok Imagine 1.5 Fast Video Extend is best for

Longer sequences
Chain extensions onto an approved opening rather than regenerating a longer video from scratch.
Alternate endings
Branch from the same extend_at with different prompts to compare continuations.
Quick continuations
Preset mode adds a beat without writing a prompt at all.

Grok Imagine 1.5 Fast Video Extend limitations

Extend only accepts task IDs from Grok Imagine Video (xai/grok-imagine-1.5-fast-video, the speed-optimized 1.5 build). Task IDs from Grok Imagine 1.5 Video are not supported; continue those, and any other clip, by URL with Grok Imagine 1.0 Video Extend. Extensions are fixed at 6 or 10 seconds, and preset mode offers only spicy or normal. In custom mode all three of prompt, extend_at, and extend_duration are required; in preset mode they are ignored entirely.

Grok Imagine 1.5 Fast Video Extend API examples

Call Grok Imagine 1.5 Fast Video Extend from any language by POSTing to /v1/tasks. Full parameter docs live at docs.unifically.com/models/video/xai/grok-imagine-1.5-fast-video-extend.

Custom mode — you control the prompt and the timing:

curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "xai/grok-imagine-1.5-fast-video-extend",
    "input": {
      "task_id": "abc123def456",
      "prompt": "The camera pulls back to reveal the whole street as the rain stops.",
      "extend_at": 4.5,
      "extend_duration": 6
    }
  }'

Preset mode — the preset drives the style, and prompt, extend_at, and extend_duration are ignored:

curl -X POST https://api.unifically.com/v1/tasks \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "xai/grok-imagine-1.5-fast-video-extend",
    "input": {
      "task_id": "abc123def456",
      "video_preset": "normal"
    }
  }'

Successful submission returns a task_id of its own. Poll GET /v1/tasks/<task_id> or set a callback_url on the request to receive the finished video URL.

FAQ

Questions fréquentes sur Grok Imagine 1.5 Fast Video Extend

It continues a video Grok Imagine already generated. Pass the task_id of the completed generation and either let a preset drive the continuation, or specify the prompt, the second to branch from, and how long to extend.

Only videos generated with Grok Imagine 1.5 Fast Video (xai/grok-imagine-1.5-fast-video), by task ID; the continuation renders on the same 1.5 engine. For Grok Imagine 1.5 Video, 1.5 Lite Video, or any clip from elsewhere, use Grok Imagine 1.0 Video Extend, which takes a video URL.

It was renamed to xai/grok-imagine-1.5-fast-video-extend on 18 October 2026 so the key names the engine. The old key is no longer accepted and a request to it is rejected with a message naming the new one; parameters and prices are unchanged.

The two modes are mutually exclusive. Provide video_preset and the preset controls the style, while prompt, extend_at, and extend_duration are ignored. Omit video_preset and you are in custom mode, where all three of those are required.

6 or 10 seconds per extension, set with extend_duration in custom mode.

It is the second in the source video the extension branches from, as a decimal. It lets you continue from a point before the end rather than only from the final frame.