Sounds like Vlad is willing to offer up a “volunteer” GRU officer to come stand trial. Somehow I don’t think Mueller wants to do that.
Yes, there is an extradition treaty between the United States and Russia. It calls for Jeff Sessions as Attorney General to make a direct request to the Russian Prosecutor General Chayka Yury Yakovlevich to send a wanted person over for for trial. Apparently the Russians do extradite. https://eng.genproc.gov.ru/
However, the treaty does provide a mechanism for Russia to claim that the extradition would compromise national security interests, and on that basis the Procurator can refuse.
He said Mueller was welcome to send a team to Russia to participate in the investigation. Let’s see if Mueller takes him up on it. I bet they don’t