Animal Companion advancement question

[PrGo]

I'm making a Kobold ranger variant and I'm planning to spec him for mounted archery. And at level 4 he'll get the Dire Weasel companion. Then I read the statistics of it and it says that it becomes large at 7 HD.
So I was wondering does it have to become large or..? (since its more in my interest that it stays just one size category bigger)

Thanks in advance.

[Emy]

Nope, it doesn't have to become larger. In fact, it cannot become larger through bonus hit dice granted by the druid.

(See the main 3.5 FAQ, page 14)

[PrGo]

Oh. Thank you, that solves that

[Tsotha-lanti]

Animal companions do not increase in size as they gain HD. Larger animals are simply larger specimens, which comes with more HD. An animal companion doesn't magically swell up into a bigger animal. The play-balance of the ability assumes that they do not change in size due to HD increase (which comes with huge increases to Str and nice ones to Con; Dex penalties are outweighed by natural armor bonuses).

[LibraryOgre]

Think of an animal companion's HD gains as being similar to your HD gains for levels. A kobold of 12 HD isn't going to be medium just because he's gained a number of levels.