Got an Alaskan husky 10 days ago. Met his parents, both big dogs with long limbs.
His weight was 4.3kg at 12 weeks. Vet said he was healthy but underweight. Now (13 weeks) and he is 5.5kg. I dont feel like he is growing or filling out at all despite great appetite. A friend commented that he might not get bigger than 12 kg..

No experience with huskies. The Norwegian Elkhound I had grew steadily and fast till he was about 25kg.

What do you guys think?

Other than seeing some *big* ears he's going to have to grown into, I see nothing unusual.

Bear in mind a few different things, Huskies are a MEDIUM sized breed so one that's over, let's say, 25kg is going to be an unusually big Husky. You're trying to judge from way too little information - some dogs start off small and stay small, some start off small and just seem to continue growing - he should grow up till about a year old and then start to fill out. As a young adult and puppy, he's much more apt to look like a beanstalk than otherwise - it's just the general nature of the breed.

Also, *in general* vets don't know that a Husky is supposed to be sveldt not husky. Many will look at a healthy working Husky and swear that they're underweight - when they're not.

Welcome to the forum and say "Hi!" to that pretty young thing.