No official word yet, but:
Variety reports that HBO has let their contractual options lapse on the cast of DEADWOOD, which begins airing its third season in a few weeks. This decision frees the cast to pursue jobs elsewhere, which strongly suggests that HBO has lost interest in a fourth season of the show before the third season has even aired.
HBO insisted that conversations about future cycles of "Deadwood" are ongoing, and Milch told the Boston Globe in the April 30 issue that he had always planned to exit the series after the fourth season; he has been reported as saying that he'd envisioned each season as a year, and the actual Deadwood camp was destroyed at the end of four.
"If a series is successful, the commercial interest is in keeping it on, even after the creative interest is in ending it," Milch told the Globe. "With 'Deadwood,' my intention is to end at the end of the fourth season. I can't speak for anyone else, but that's where I'm getting off the bus."
I really hope this is just a rumor, or perhaps a publicity stunt.