It's not mandatory. However, when I was at Google several years ago, it showed up on my calendar, it was not optional, my manager said that I was expected to attend, and I attended. But it's not mandatory.
So is it ""not mandatory"" then ?
Of course it's mandatory ... unless you don't care about silly little things like bonuses and promotions.
It's not mandatory.
It sounded like it was a mandatory part of managerial training.