When was the last time you saw a jazz musician electrify a crowd? For me it was a couple of weeks ago, during Esperanza Spalding’s exultant concert at Town Hall, in midtown Manhattan. Singing the deftly intricate songs from a new album, “12 Little Spells,” she was the picture of vital intensity well before the encore, when she re-emerged in a jumpsuit emblazoned with the catchphrase “Life Force.”

Ms. Spalding is exceptional in every sense of the word, but she’s also part of a cresting wave. The music we call jazz has been undergoing an explosion of creative possibilities, carried out by musicians with an impressive range of new skills and ideas. Some of them have found traction with impassioned young audiences, achieving a rare balance of popular success and critical approval — enough, in some corners, to bring talk of jazz’s new golden age.

I just wrote a book about jazz in the new century, so I might be waving that banner, too. The music’s plurality of style, embodied by Ms. Spalding and so many others, amounts to an extension of the jazz tradition rather than any kind of heretical crisis. The music is meant to evolve, and we’re in the midst of its most wildly adaptive, thrillingly unruly evolutionary phase in some 40 years.

So why do I balk whenever someone declares that jazz has entered another golden age? On some level it’s reflex: a resistance to hyperbole, and an awareness that whatever my convictions, we don’t have enough distance to see our moment with total clarity. On some level, too, it’s wariness about any exercise that weighs one era against another, brushing aside the broader context.