Why sume/auto never picks H3 Max Recast, and what to send

Auto picks for prompts, Recast needs inputs

If you call Sume with model: "sume/auto", Sume chooses the video model from the request. That works when the request is a prompt, a first frame or references. A person swap is different: it needs one source video and one to four photos, one per new person, and it has no text-only mode.

Sume's design notes for the Video Router say the rows that take a source video_url besides Gemini Omni Flash 1.1 are Genjutsu and H3 Max Recast, that both are explicit picks, and that sume/auto never routes to them. The Auto code in the repository has no Recast branch, which matches the note.

The request that works

Send the catalog id h3-max-recast to the Video Router. The Video Router docs describe it as swapping the people in a source video_url for 1 to 4 reference_image_urls, one photo per person, at 768p or 1080p, with the prompt optional. The duration is the source length, 5 to 30 seconds.

Read the catalog first. GET /v1/video-router/models returns capabilities, so you do not have to trust a blog post for the envelope.

curl -X POST https://api.sume.com/v1/video-router/generate \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: recast-001" \
  -d '{
    "model": "h3-max-recast",
    "video_url": "https://example.com/source.mp4",
    "reference_image_urls": ["https://example.com/new-presenter.jpg"],
    "resolution": "768p",
    "duration": 12,
    "mode": "async"
  }'

What fal says about the model

fal's page, read 2026-10-03, describes Recast as recasting the people in a video with reference photos while preserving the source motion, camera, cuts and audio, at $0.30 per second at 768p and $0.45 at 1080p. fal's own default is 1080p. Sume sends the resolution every time and defaults to 768p, so a request that omits it stays on the cheaper tier.

Checks before you pay

• The model id is h3-max-recast, not a prompt that says "swap the person".
• duration is the source length rounded up, between 5 and 30.
• No single shot is over 15 seconds, per the Sume catalog constraints.
• Do not send aspect_ratio, generate_audio, bitrate_mode or model_params; Recast rejects them.
• Keep the Idempotency-Key when you retry a timed-out submit, so you do not pay twice. See Jobs and results.