He's trying to get himself attention, and succeeding it would seem as here's a story on it.
Assange has acted rather oddly throughout this whole thing, at least if you take his rhetoric at face value. He happily went to Sweden and spent time there until these allegation came up, at which time he went to the UK. He then claimed that the reason was that the charges were BS and Sweden would just hand him over to the US because they were after him as soon as he went back. That of course makes one questions:
1) Why would he go to Sweden in the first place, if he knew it was a country that would hand him over to the US extra judicially?
2) Why would he flee to the UK and feel safe there, a country with such a special relationship with the US it is literally called the "special relationship"?
He then fought the extradition to Sweden in the UK courts and lost. They were ruling just on the validity of the extradition request, not on the validity of the charge behind it. He then fled to the Ecuadorian embassy, claiming that he'd be handed over to the US if he went to Sweden.
So there we are today. Now near as I know, the US has not sought his arrest. While they don't like him, it doesn't look like he's broken US law. Publishing classified US information isn't a crime if you weren't the one who had access to it. So a guy who has a security clearance and gets information and gives it to a paper, he's breaking the law. However the paper that then publishes it is not.
Now maybe he really does know something most don't, but it seems more likely this is just him trying to get in the news. He knows this is an empty offer since the US wouldn't agree to it as they don't have a valid charge to bring against him. This is all between him and Sweden and now him and the UK (even if Sweden dropped the charges, he still broke UK law be fleeing his bail). The US isn't involved.