At a sold-out event on Monday in Manhattan celebrating the centenary of the free expression group PEN America, there were as many literary luminaries in the audience as there were onstage.

Before intermission, Margaret Atwood, dressed in metallic sneakers and a bright pink shirt, had engaged in some salty, friendly needling of Dave Eggers over whose dystopian novels were more prescient. At the break, Tom Stoppard and Neil Gaiman were spotted in a floppy-haired tête-à-tête, while Robert Caro and Paul Auster passed nearby.