Apple is offering developers 50GB of free iCloud storage so that can test new features such as iCloud Drive and iCloud Photo Library. The offer is temporary and expires on November 1st, 2014, and it's open to registered developers.
From Apple's developer site:
When you sign up for iCloud, you automatically get 5GB of free storage. As an Apple Developer you can get 50GB of temporary additional iCloud storage to try the new iCloud features such as iCloud Drive and iCloud Photo Library. Sign in to developer.icloud.com with your developer account to receive an additional 50GB of temporary storage until November 1, 2014. Current membership in the iOS Developer Program or Mac Developer Program is required.
Apple announced iCloud Drive on Monday during the company's annual World Wide Developer Conference keynote, a service that essentially lets users see those documents stored on iCloud. iCloud Photo Library is a service tied to new photo sharing features between a user's iOS and Mac devices.
Apple said that accounts would revert to their original storage plan after November 1st.