Specs match Steamworks requirements as of 2026. Valve occasionally changes capsule sizes, so do a final check in the Steamworks art upload screen before submitting for review.
Size isn't the only rule. Store capsules may contain only game art, the game name and an official subtitle: no review scores, award laurels, "on sale" text or promotion of other games. Breaking this limits your visibility and blocks featuring in Steam sales. Library heroes take no text at all. For temporary update or event text, use an Artwork Override (max one month, localized).