Download-only Xbox One titles will have 1000 Gamerscore, the same amount as a full retail release.
A recently released list of Halo: Spartan Assault‘s Xbox One achievements (via X360A) confirmed the change. The Xbox One version of the game has 1000 Gamerscore worth of achievements, whereas the Xbox 360 version only has 400–the current limit for XBLA titles.
PopCap Games also confirmed that its upcoming title Peggle 2 would have 1000 Gamerscore worth of achievements.
@NBAKirkland 1000 is the answer! Confirmed by the producer himself.
— PopCap Games (@popcap) November 8, 2013