Windows 8.1 build 9374 leaked online today. The build has been labeled as "Windows 8.1 Pro Preview" which indicated that Microsoft is planning to release a free preview version of Windows 8.1 before the final launch. Windows 8.1 build 9369 was also leaked a few days ago showcasing an SKU of "Windows 8.1 Pro."
For those curious, the build string of the latest version is 6.3.9374.0 (fbl_partner_out15.130329-2355) with a build date of 03/29/2013.
There’s no info on the release date, but the BUILD developer conference scheduled to take place in June in San Francisco is very likely to witness the debut of the beta, while the full release could arrive in August or September.