Larian has been releasing a patch every 2-3 months though recently the progress has slowed down - my guess would be that Larian gathered a lot of feedback they were looking for and now focus primarily on finishing the game.
If you exclude the first couple months after EA released, Larian has fairly consistently released a patch every 4 months.
The most recent patch (#7; Barbarian) was on Feb 15, so right now they're only a ~week later than their past schedule.
Has Larian indicated when we will get the next major update?
Larian typically makes a Patch and/or PfH announcement 1 week before it happens. They don't offer much more warning than that.
