Even as it prepares for its 40th anniversary tour this summer, Yes is working on new material, frontman Jon Anderson has revealed to Billboard.com.

Anderson says the progressive rock heroes are preparing four new songs of the "opus" variety -- lengthy, multi-movement compositions along the lines of "Close to the Edge" and "Tales From Topographic Oceans."

"They're very, very different," Anderson says. "It'll be interesting when we perform them, because we know that we want to try and perform them in a unique fashion."

But Anderson adds that he's not sure those songs will wind up comprising Yes' first set of new material since 2001's "Magnification."

"Putting together an album really isn't logical anymore," he notes. "Putting together a large piece of music or something that is really a jump in a musical direction takes a lot of commitment from everybody.... But maybe during the tour we will discuss making some new music."

Anderson says he'd also be amenable to some sort of reunion of the Yes lineup that made the group's triple-platinum 1983 smash "90125" as well as 1987's "Big Generator" and 1994's "Talk."

He and Trevor Rabin, the guitarist and co-producer in that incarnation of the band, have been in discussions about "maybe touring some of that '80s-period music, because it was very special."

But Anderson says he and Rabin aren't necessarily thinking about resurrecting that version of Yes as a recording entity.

"I wouldn't do it, like, Yes," Anderson explains. "I'd do it like me and Trevor aspiring to be the two of us making music and see what we come up with.

The Yes anniversary tour kicks off July 12 at the Festival d'ete de Quebec in Quebec City.