Apple originally acquired FoundationDB in 2015, and last April it announced that it was making the cloud database open source. Now, things are being taken a step further as FoundationDB has announced it is open sourcing Foundation DB Record Layer, which powers CloudKit.

This is the first public confirmation from Apple that CloudKit is powered by FoundationDB. The company touts that Record Layer is used by Apple to “support applications and services for hundreds of millions of users.”

Today we are releasing the FoundationDB Record Layer, which provides relational database semantics on top of FoundationDB. This layer features schema management, indexing facilities, and a rich set of query capabilities. The Record Layer is used in production at Apple to support applications and services for hundreds of millions of users.

Together, the Record Layer and FoundationDB form the backbone of Apple’s CloudKit

FoundationDB has also released a full paper that goes incredibly in-depth on the details of how CloudKit uses Record Layer. For instance, FoundationDB touts that Record Layer operates in a “completely stateless manner,” which means tasks like instantiating a logical database and performing an operation take just milliseconds.

The full paper can be read here and more details about the open sourcing process are available in the full FoundationDB announcement.