Definitely not a purebred pittie - he's cute as can be, but he doesn't have the broad face of a pittie, and his nose is too long. Something narrower-faced mixed with brindle-pit perhaps, and of course all cuteness! If he has webbed toes, maybe that's why the vet guessed Lab, but we'll see how big he ends up before making and other guesses! Give him a kiss for me!

Your vet, however, may have been doing you a kindness, in terms of insurance and other matters, "mixed breed" is better than pitbull mix, and indeed, maybe he is a boxer mix - from the coloring, that could be it, too, but his face and muzzle is definitely not a bit boxerish!