As indicated in the official support document, Apple has now raised the previous iCloud Contacts limit from 25,000 contacts to 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.
These contacts can be shared and synchronized with iPhone, iPad and iPod touch devices, as well as synchronized with the iPhone, and can be accessed at iCloud.com.
How to Export Contacts from iCloud
How to Restore Contacts from iCloud
The syncing limits for calendars, reminders, and bookmarks remain unchanged. Apple currently allows up to 25,000 calendars, events, and reminder entries, 100 calendar and reminder lists, and 50,000 vCards in your address book. These types of data are stored and kept up-to-date across iOS devices, Macs, and the web without consuming the 5GB free storage.
I certainly don't have 50,000 contacts on my iPhone, but if you do, then it's your lucky day!