Do bear in mind that personalized suggestions in this particular update does not translate to the personal dictionary that is already available, and is synchronized to the rest of your various devices over Google’s cloud.
This particular update would bring along with it personalized suggestions that Google has already picked up from your usage of other Google products. The feature has been turned on by default, although fret not as the keyboard does offer you a very prominent warning the first time you use it after the update has been applied. I suppose this is important so that one can avoid potentially embarrassing situations, especially if you use less than savory words on the other Google products and services such as Gmail, Calendar, Google+, and Drive. This particular update is said to be introduced in the days ahead, so some patience would be required.