Early Release & Promos
Full boxes of Set Boosters will be available for early pickup and purchase during Strixhaven Prerelease, April 16-22.
Each box of Set Boosters will be accompanied by the Strixhaven Buy-a-Box promo and a Kaldheim Promo Pack (while supplies last)
(no action required, buy-a-box promo & promo pack will be automatically included with purchase)
With a focus on excitement and collecting, Set Boosters contain fourteen cards, twelve of which are playable Magic cards (in contrast with a Draft Booster, which comes with sixteen cards, fifteen of which are Magic cards).
Get more details in the third image for this item and this article from Wizards.
Each Set Booster Box contains 30 Set Boosters