As indicated in the official support document which was updated last evening, Apple has now doubled the previous iCloud Contacts limit from 25,000 contacts to 50,000 items.
These contact cards can be shared and synchronized with the iPhone, iPod touch and iPad devices, as well as with Mac and Windows PCs, and can be accessed through any modern web browser at iCloud.com.
iCloud Contacts now supports 50,000 contact cards in total, with a maximum size of a contact card set at 256KB, a contact photo at 224KB and a contact group at 256KB.
The total size of all the photos attached to your contact cards cannot exceed hundred megabytes, or 24 megabytes in the case of card text. iCloud Contacts supports JPEG, BMP, PNG and GIF file formats for a contact photo.
Similarly, the previous vCard import limit of 25,000 contact cards has been raised to 50,000 items. The maximum size of a vCard can be 256 KB, which includes both the profile photo and text, with the maximum vCard photo size set at 224KB.
Should you exceed one or more of the limits mentioned above, iCloud Contacts might have issues keeping changes up to date across your devices.
Limits for iCloud Bookmarks (25,000 items) and iCloud Calendars and Reminders (25,000) have not been raised at the time of this writing.
Source: Apple via iFun.de (Google Translate)