The Gleeful Grognard wrote:
For the bear, it is 8 (ancestry) + 8xlevel (6+con=8). As with characters if you increase its con mod it will retroactively improve its hp like a player would.
So a level 3 character with a bear companion would have a bear with 24hp.
Do you know what page it says you retroactively increase you HP when you increase your Con with an ability boost? I have been looking and I can't find it.