UPDATE: Microsoft has confirmed the below report, with Xbox Live mouthpiece Larry "Major Nelson" Hryb saying on his blog that the changes will be optional from next mont, and mandatory from June onwards.
Microsoft is set to double the number of Achievement points available in Xbox Live Arcade games, according to reports.
A source told Xbox 360 Achievements that all games released on the service from June 1 onwards will offer a maximum of 30 achievements and a total of 400 Gamerscore, up from 20 and 200 respectively.
Under the current rules, developers can release a maximum of three DLC packs, each containing up to five achievements worth a total of 50 points, each quarter. When the new rules come in, the DLC limit will rise to four, with a maximum of eight achievements worth 100 Gamerscore.
It's a sensible move given that the Achievements system has remained broadly static while the size and scope of XBLA games has improved dramatically since launch. As prices on the service have risen, it seems appropriate that the size of the rewards on offer should increase as well.
Developers of games released in May, before the new terms come into effect, will be given a choice of which system to use, the source claimed.