YouTube video A/B testing: up to three cuts or thumbnails

YouTube says it is coming soon: a video A/B testing feature to test up to three video cuts and see which hook performs best. What exists today is the title and thumbnail test, where creators can test and compare up to 3 different titles and thumbnails.

Both facts are from YouTube's own pages, read 2026-09-29: its blog post new tools across the creation journey and the help page A/B test titles & thumbnails. The Sume part is from the Video trim docs.

What has YouTube announced for video cuts?

The blog post says: "Coming soon, you'll also be able to test up to three video cuts to see which hook performs best with the new video A/B testing feature." It gives no start date and no rules for cuts. The same post says creators have run more than 40 million experiments on titles and thumbnails since that feature launched in 2024, and mentions dynamic thumbnails, where YouTube recommends one of three thumbnail options to different segments of your audience.

Because the blog post gives no rules for the cut test, none are stated here. Use the current title and thumbnail rules as a guide only.

How does the current title and thumbnail test work?

YouTube says tests are optimized for overall watch time rather than click-through rate, and that testing titles and thumbnails that are too similar can make a test run longer.

Can I A/B test a Short?

Not with the current tool. The help page says A/B testing is not available for Shorts, and that once a video transitions to a Short you lose access to earlier tests. It adds that uploads up to three minutes that are square or taller are considered Shorts. Whether the coming cut test covers Shorts is not stated.

How do I prepare three cuts of a video with Sume?

Sume's Video trim cuts a clip from a Sume-hosted video: video_url (this workspace's media.sume.com file), start in seconds and exactly one of end or duration (0.2 to 900 seconds). Run it three times with different in-points to get three openings. The call needs an Idempotency-Key.

For thumbnails, generate three 16:9 images from three prompts (see AI thumbnail generator for YouTube), and keep each at 1280 x 720 or larger so YouTube does not downscale them.

curl -X POST https://api.sume.com/v1/video-trim \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: cut-b-001" \
  -d '{
    "video_url": "https://media.sume.com/artifacts/artf_demo/talk.mp4",
    "start": 12,
    "duration": 45
  }'