Microsoft opened up registration for its 2014 Build conference yesterday, and it has sold out just over 24 hours later. This year’s event takes place in San Francisco again, but Microsoft will play host at the Moscone Center between April 2nd and 4th. After holding Build 2013 in June, Microsoft is pushing its annual event forward a couple of months this year and is expected to unveil Windows Phone 8.1 alongside some initial Windows 9 details.

Windows Phone 8.1 includes a notification center and Siri-like personal assistant, with lots of additional tweaks compared to the original release in October 2012. Microsoft will also likely detail its upcoming "Update 1" release for Windows 8.1 at Build 2014. The update is expected to include fairly minor changes to Windows 8.1 ahead of a larger Windows 9 release in early 2015. Developers are clearly eager to hear more about Microsoft’s changes after registration sold out just TKTK. With continued Surface mini rumors and Nokia’s first Windows Phone 8.1 handsets on the way it’s possible that Build 2014 could include a mix of hardware and software announcements this time around.

Update: Microsoft confirmed the sell out to The Verge in an email. “Size and scope is comparable to last year, but we’re not sharing specific numbers,” says a Microsoft spokesperson. At Build 2013 over 6,000 developers attended the show.