“I’m pragmatic,” Mr. Glass said. “I don’t know what’s going to happen in 10 years. We don’t even get to know what’s going to happen after someone dies. We need to wait until everyone who knew them is dead, too.”

If that’s true, it won’t be until nearly 2100 when a full measure of Mr. Glass’s footprint will be possible. But some weighing can start now. The most instantly recognizable voice in contemporary music, he opened a new chapter in operatic history, pushing the bounds of duration and abstraction. At a time when the most lauded composers disdained overproduction, Mr. Glass wrote unashamedly for everyone and everything — and all stubbornly in the distinctive style he created, establishing a model for serious artists moving from the opera house to the concert hall to the film studio, garnering both Met commissions and Academy Award nominations.

But if the question is whether, a century from now, his operas will get new productions, his symphonies will circulate more frequently, or pianists will take on his études, Mr. Glass couldn’t care less.

“I won’t be around for all that,” he said. “It doesn’t matter.”

MR. GLASS WAS BORN, almost literally, into music: His father owned a record store in Baltimore, where the composer-to-be absorbed Beethoven, Schubert, Bartok, Shostakovich and Stravinsky — and, perhaps, an intrinsic connection between art and commerce. Over a few years in Paris, Nadia Boulanger was his composition teacher as he was exposed to the jittery-fly modernism of Boulez and Stockhausen. He didn’t hate them, but he didn’t want to compose like them, either.