Grok Video Extend

Grok Video Extend answers one very specific question: what happens next? You feed it a video and a prompt describing the next beat - "the car drives through the gate", "she turns and smiles" - and it produces a seamless continuation, not a hard cut or a generic fade. It's the sibling of Grok Video Edit: Edit changes what's in a clip, Extend keeps the shot alive past the last frame. Both are built-in partner nodes, meaning cloud API calls through your Comfy account rather than anything running on your GPU.

This is the node you want when you've generated a clip you love but it's two seconds too short, or when you're building a longer sequence out of stitched-together segments and want the joins to feel continuous. The model sees your source video as the opening of the story and invents the next chapter with matching subject, style, and motion.

The inputs

• video - your source clip, MP4, 2–15 seconds (per the tooltip). The lower bound matters too: a 1-second clip is too short to establish enough context for a convincing continuation.
• prompt - text describing what should happen next in the video. This is where you set the next shot's action, and it's the difference between "seamless" and "the model wandered off."
• model - the Grok model to use for extension (a dropdown that populates from the API).
• seed - as with every node in this family: it only controls whether the node re-runs, not the outcome. Results are nondeterministic regardless of seed.

What comes out

One VIDEO output - the original clip plus the continuation. Save it, preview it, or chain it: you can feed the extended clip right back in for another extension if you're building something long. A common pattern is Edit → Extend → Extend to assemble a scene from a single seed clip.

Gotchas

• The 2–15s window is enforced. Outside it the node errors before billing. Trim or pad first.
• "Seamless" is a goal, not a guarantee. Long extensions can drift in character design or lighting, especially if your source clip is busy. Keep the prompt consistent with the source's style.
• Each extension is a separate paid call. Stitching a long sequence this way adds up fast - it's a cloud API billed per call through Comfy credits, so plan the sequence before you commit.

That's the whole workflow: source clip, one sentence about the next beat, and a longer video comes out the other side. No install, no vendor key - it ships with ComfyUI core and just needs your Comfy account logged in.