Great news! Sorry to the True Leftists who hoped he'd help install President Walker though.
I don't think it's news. It sounds like they're just repeating speculation, since everyone expects that he would run as a Democrat. But they don't quote Sanders directly. Sanders himself has never given any kind of firm commitment on whether he would run as a Democrat or an Indy. Publicly, at least, he says he's open to both.
He stated in the article that there shouldn't be an uncontested primary, which obviously is an implication he'd be running as a Dem. He's also been visiting IA/NH, would be pointless if he was running as an indie.
I know, and that's why everyone assumes that he's running for the Dem. nomination. I expect that he'll run for the Dem. nomination. I'm just pointing out that, whenever he's asked on the record whether he'd run as a Democrat or an Independent, he always says that he's undecided, and could go either way. All of his actions to date suggest that he's running as a Dem., but just wanted to clarify that his "official" position is that he's undecided on that.