confirmed / effective unknown
YouTube thumbnail recommendation now lists 3840 x 2160
The current YouTube Help page lists 3840 x 2160 as the recommended custom thumbnail image size. Older creator guidance and many tools still reference 1280 x 720, so this row keeps the change visible while the effective date remains unknown.
Before
1280 x 720 was the long-running creator-tool baseline for 16:9 thumbnails.
After
YouTube Help currently recommends 3840 x 2160 at the same 16:9 ratio.
Evidence
Published 2026-06-29; last checked 2026-06-29; verified false because the effective date is unknown.
YouTube Help: Add video thumbnails