Do you think he is mixed with something?

He looks to me like he's got some Shepherd or Mastiff in him.

Because pits aren't a recognized breed. there are no true set standards for them. This means that there are many physical differences between them. You could have a pit from a long line of pits that have been breed for the stockyness and be a "purebreed" and also have a pit that was bred for the more agilty and slim appearance that would also be a "purebreed" and have two completely different looking pits.

I guess what I'm trying to say is that it could be all pit, but not really what members of many kennel groups would recognize as a pit based purely on appearance. Then again, it is possible to have another breed in there somewhere, and it's pretty much impossible to say for sure unless you can track the lineage.

Pit Bull is not actually a recognized breed -- therefore they come in many different varieties, shapes, sizes and colors. It's possible that he is mixed with something, but it's also possible he's just a variety of pit bull.

Mastiff mix

i think he's got some lab in there.