It's still too fresh, so wait for it to harden up because the colors are still too light since he's freshly molted. Hard to say what Brachypelma he/she is since a good majority of the red rump Brachys look alike.
Unfortunately i don’t think a definitive ID can be made off of a picture. Best somebody can say is it COULD be a vagans. But IIRC there are several species (such as B. sabulosum) which will look seemingly identical to B. vagans and i would assume that features such as spermathica shape would beed to be used to properly ID.
Disclaimer: i am not a taxonomist and my knowledge of taxonomy is sadly very lacking so take everything i say with skepticism.
@Theneil I would assume that one asking for a I. D. By photo knows that's all the data we have to make the guess. If they don't include pics of spermatheca and other parts of the t the best we can do is guess based on the image provided.
@Noah Blades I realize that people do the best they can, but there are a lot of people that will just assume the first suggestion is correct and label as such because they may not know that there are so many similar looking species. I just wanted to make sure they are aware that certain species cannot be diffinitively ID’d by pictures.