Reid Wilson at Hotline is hearing the same thing: that Murkowski is announcing her write-in candidacy this evening.
This was going to be a close race where Joe Miller has an edge. With Republicans split, my guess is that Democrat Scott McAdams would be the frontrunner (though by no means a shoe-in). If I were in the Senate GOP leadership, I’d be calling up Murkowski right now and telling her that she should seriously consider announcing that previous reports were erroneous and she is endorsing Miller, and that if she goes through with this write-in candidacy, in the event she wins she will be treated like a first-term senator and be last in line for committee assignments. If moderates won’t grow up, maybe they need to be treated like misbehaving children.