OpenZFS/ZFS on Linux diverged after version 28. They now use version 5000, and use feature flags instead of version numbers to allow different implementations to add their own improvements. Oracle has added some features since then as well, notably: encryption, large blocks, resilvering performance improvements, and device removal. All of these features have also been implemented in ZFS On Linux.

https://en.wikipedia.org/wiki/ZFS#Detailed_release_history

http://www.open-zfs.org/wiki/Feature_Flags