Chris Thile already has a full plate as it is: mandolin maestro with prog-grass all-stars the Punch Brothers, singer-songwriter, eager and frequent collaborator, curator of The 65th Street Session. He has no obligation, commercial or otherwise, to resurrect Nickel Creek, the perpetually underrated acoustic trio that launched his career back in the early 2000s. But that fact alone makes Celebrants, the band’s fifth major album, so heartening: It exists because it simply had to— reflecting the gravity of chemistry between Thile’s mandolin, Sam Watkins’ guitar, and Sara Watkins’ fiddle. “It’s been too long, stranger,” Sean sings early in the record, seemingly winking to fans about the near-decade since 2014’s A Dotted Line. And Celebrants, while as fluid and harmonious as anything they’ve recorded since “Smoothie Song,” flexes the artistic ambition of musicians nine years wiser, more studious, more eager to explore. If A Dotted Line—itself a nine-years-later reunion project, following 2005’s Why Should the Fire Die?—came across like old friends swapping riffs on a front porch, then Celebrants sounds like that same group, after sharing a joint and hours of stories, getting down to business. It’s 18 songs full of connected themes (friendship, for one), musical reprises, tightly woven harmonies and modest virtuosity—in a sense, it’s Nickel Creek with more Punch Brothers in its blood, reflected in the woozy harmonic gestures of “The Meadow,” the massive dynamic swings of “Goddamned Saint” and the robust instrumental solos of “Going Out…” It might be their masterpiece