Druid companions

[Wippit Guud]

"An animal companion gains additional skill points and feats for bonus HD as normal for advancing a monster’s Hit Dice."

What about size increase for applicable animals?

 

[Jeff Wilder]

"An animal companion gains additional skill points and feats for bonus HD as normal for advancing a monster’s Hit Dice."

What about size increase for applicable animals?

I'd assume not. First, it's not explicitly listed. While that's of course not dispositive, also consider 3E's version of high-level animal companions: legendary animals. They were the same size as normal animals of their type, despite being immensely more physically capable. I think the intent is just that the animal gets more capable, not actually larger and bruiser-ish.

 

[shilsen]

No size increase. WYSIWYG.

 

[jgsugden]

Andy Collins (look at your 3.5 PHB credits) has said that companions do not increase in size, though they gain skill points, feats and ability score points for gaining hit dice just as any other advancing creature would.