There had been chatter that Bulletstorm would be one of several Epic Games titles whose achievements would trigger unlockables in Gears of War 3, due at the end of the year. Those plans have been scrapped because of compatibility issues.
Epic's Joe Graf, a lead gameplay programmer, tweeted that Gears of War 3 cannot read the achievements of Bulletstorm, Shadow Complex and Unreal Tournament 3 after all. "Sorry about that all," he said.
The reason is that, while Xbox Live exposes data through a player's gamercard, going deeper requires an unsupported manipulation of the servers. Bulletstorm, Shadow Complex and UT3 are classified separately from Gears of War, placing the achievement link-up outside Epic's control here.
Graf did confirm that achievements in all previous Gears of War games will count toward unlockables in Gears of War 3.
Epic Cancels Bulletstorm Unlocks in Gears of War 3 [Official Xbox Magazine via RipTen]