Rare Replay, the anthology of 30 games spanning 30 years of the studio's history, does offer 10,000 Gamerscore as claimed — if you account for the 7,220 Gamerscore already offered by games that have previously launched on Xbox 360.
Rare's James Thomas, in an interview with Rare Gamer, clarified the 10,0000 Gamerscore claim, acknowledged that Gamerscore previously earned on Rare games that are part of Rare Replay already count toward the total Gamerscore offered. "The benefit of this is that you get to use your existing achievements to get a head start in unlocking the bonus content within Rare Replay," he said.
"The 360 games are as they currently are on the 360, nothing added or taken away," Thomas said.
The achievement-tracking site TrueAchievements counts 150 new achievements worth a combined 2,780 Gamerscore (one is, delightfully, "Do You Have Battletoads?" offering 15 Gamerscore simply for playing that game.)
More remarkably, Thomas says the save files from Rare's previous Xbox 360 titles (Viva Pinata and Perfect Dark Zero are two) can be transferred to the Xbox One collection. "Your saves carry across too, thanks to the wonders of the cloud," he said. "If you saved it up there on 360, it'll be there on Xbox One."
Rare Replay launches on Xbox One August 4. The earliest games it features are Jetpac, Atic Atac and Lunar Jetman, from 1983. The latest are Banjo-Kazooie: Nuts & Bolts and Viva Pinata: Trouble In Paradise from 2008. For more, see Polygon's preview from E3 2015.