Five years ago, sitelinks were introduced for YouTube in-stream ads on mobile, but they’ve only now started appearing on desktop.
Hana Kobzová spotted sitelink extensions appearing on desktop just below the companion banner, displaying the headline and a one-line description on a greyed-out background.

There’s no minimum number of sitelinks required. Hana saw this section with just one sitelink.

Just a reminder: this same space is also used for dynamic remarketing, as observed in October 2024.