Today 17.10.2018 K2 5.2 went into GA stage meaning news about release were sent to all clients and partners and starting from now we can download this new and shiny version from K2 portal. So it is a perfect time to do a little review. Without further ado let me start with this.
You can download 5.2 installer from K2 portal. And providing you have test VM with current version of K2, update manager will get you to new version withing 30 minutes or so. Once installer completes extraction of files you presented with splash screen:

Splash screen provides you with essential information (.NET 4.6.1 requirement, where to run an so on) and allows you to kick off installation process (conservative people like me can still locate Setup.exe and run it from Installation folder).
In case of existing installation detected K2 Update manager detects that and gets you upgraded just in few steps:


In case you run with multiple security labels you will immediately notice improved label selection UI which is no longer looks like something from the past and fully aligned with modern K2 UI design:

Additionally you will notice increased number of available OAuth resource types:

My favorite under the hood improvement, which is really huge thing, is completely rebuilt identity cache and sync architecture which was brought into on-prem product from its cloud version (if I employ Microsoft-speak “battle-tested in the cloud” and so on). At this stage all the internal infrastructure of new Sync Engine is already here in 5.2 RTM, yet it is disabled – stay tuned for official news for when this feature will go live for all customers. At initial stage K2 will work with selected customers to assist them to enable and transition to the new Sync Engine. But like I said, you already can see that underlying infrastructure for New Sync engine is already here in 5.2 release. In case you familiar with back end/underlying tables you can tell that number of Identity tables has increased:

And Identity.Identity table has been expanded too:

Long story short with all these changes and new sync engine enabled your Identity cache sync speed will be greatly improved and, for example, even your URM Get Users SmO call against Azure AD label can be served from cache without doing query to AAD.
There is more improvements and new features and I will try to cover them in greater details a bit later.
Additional resources / next steps:
5.2 Installation and Configuration Guide aka ICG