The shoulder strap is the giveaway. JBL is not pretending the Xtreme 4 is something you'd carry to a coffee shop. This is a speaker for the park, the lake, the tailgate, the rented Airbnb where someone forgot to bring music — and you carry it the way you'd carry a bag of charcoal, slung over one shoulder, slightly heavier than you remembered.
What JBL got right this time is the battery. The Xtreme 3 was a great speaker that became e-waste the day its sealed battery refused to hold a charge, which is a thing that happens to portable speakers around year four. The Xtreme 4 has a user-replaceable battery, and that one decision changes how I think about the purchase. I'm not renting a speaker for the lifespan of a lithium cell anymore. I'm buying a speaker, and a consumable that I'll replace once or twice over the next decade.
The sound is what you'd expect from a JBL of this size: loud, warm, slightly hyped in the bass, and coherent at high volume. I took it to a friend's backyard for a birthday and ran it for most of an afternoon at what I'd call disrespectful-to-the-neighbors volume; it never distorted, never thinned out, and the battery still had something in it when we left. JBL claims around 24 hours; I'd guess 12 to 15 at the volumes I actually use it at, which is honest enough.
IP67 is the other spec that earns its place on the box. I have dropped it in wet grass, set it down in a puddle of beer, and left it outside through a passing rain shower. It does not care. The fabric grille dries in an hour and the speaker keeps working. This is the difference between a speaker you babysit and a speaker that joins the party.
The catches. PartyBoost works only with other JBL PartyBoost speakers, not Auracast, which is annoying if you wanted to pair it with a Charge 6 (different protocol). The app is fine but unmemorable. There's no AUX input, which feels cheap on a $350 speaker. And while the speaker is rugged, the silicone bumpers on the ends pick up dirt the way velcro picks up lint — mine looks lived-in after six months in a way the Bose patio speaker next to it does not.
The right comparison is the Charge 6 at roughly half the money. The Xtreme 4 is bigger, louder, has a longer battery, and the strap. The Charge 6 will fit in a backpack. If you already know which one you want, you already know which one you want.
Verdict: Buy this if you want one outdoor speaker that's loud enough to ruin a barbecue and built to be your speaker for the next decade.