Database In-Memory is an option to Enterprise Edition. Database In-Memory now has a new "Base Level" feature. This allows the use of Database In-Memory with up to a 16GB column store without triggering any license tracking.
The feature allows you to use Database In-Memory without having to license the option. The column store is limited to 16GB when using the Base Level. This helps to show the value of Database In-Memory without having to worry about licensing issues.