When Jay Leno takes over the 10 p.m. hour of NBC’s weeknight primetime schedule this fall, viewers will get a whole new Jay: More comedy. Correspondents doing bits. Celebrity guests racing cars instead of just yakking. Yes, even the host himself will be a different man — one who’s at least 10 pounds thinner, thanks to running 4 miles a day to “get into shape” for his new gig.

On Wednesday at the annual Television Critics Association press tour, Leno unveiled some particulars of his foray into primetime to reporters. “It’ll be more intense,” he promised. “There’ll be a lot more comedy in the show.” Among the specifics: The set is bigger and the desk is gone (though it could return for his beloved “headlines” segment). “It won’t be a talk show,” he said. “But it won’t be a variety show with wigs and hats.” NBC News anchor Brian Williams — who’s shown impressive comedic chops on Saturday Night Live and The Daily Show – has committed to doing an occasional segment such as “stories that weren’t good enough to make the Nightly News.” D.L. Hughley will report on politics, while Rachael Harris (The Hangover) and Mikey Day will also tape occasional segments as correspondents. “I’m hoping we can make some stars here,” Leno said.

The celebrities who come on the show to promote their latest projects could find themselves with a lot more than talking to do. In one significant change from The Tonight Show, Leno’s crews have built a race track right next to the new studio so celebs can participate in an occasional “Green Car Challenge” — racing against each other in environmentally friendly vehicles. “Even Tom Cruise called and asked, ‘Can I get in early and practice?’” Leno joked. (Answer: No, no one gets to practice in advance.)

The extravagance of such additions shows the network’s commitment to the arrangement; NBC exec VP Rick Ludwin said the Leno experiment will last at least a year, and “we hope many years beyond that.” He wouldn’t set a specific ratings benchmark by which its success will be judged, but stressed that the net is thrilled to have Leno on its side instead of competing against Conan O’Brien’s Tonight Show for another network.

Leno, for his part, swears that while the new challenge has reinvigorated him, it isn’t stressing him out. That’s mainly because he’s not worrying much about rescuing struggling NBC, even if it has fueled his entire career. “The network is on its own,” he said, when asked if he felt pressure to “save” NBC. “There are things I like about it, there are things I don’t. But much like a marriage, you work it out. If we go down in flames, we’ll be laughing on the way down.” So what’s his secret to remaining so calm launching this show, as opposed to when he nervously took over The Tonight Show in 1992? Says Leno: “I’m rich now.”

The celebrities who come on the show to promote their latest projects could find themselves with a lot more than talking to do. In one significant change from The Tonight Show, Leno’s crews have built a race track right next to the new studio so celebs can participate in an occasional “Green Car Challenge” — racing against each other in environmentally friendly vehicles.