Apple has made iOS 7.1 beta available to developers for all compatible iOS devices which include:

• iPhone 5s
• iPhone 5c
• iPhone 5
• iPhone 4S
• iPhone 4
• iPad Air
• iPad (3rd and 4th gen.)
• iPad 2
• iPad mini with Retina display
• iPad mini
• iPod touch (5th gen.)

Apple’s iOS 7.1 release notes can be found here.