Props to DCRAINMAKER for telling it like it is:
"And while Whoop’s platform/software has largely been fantastic and innovative, the optical heart rate sensor within the Whoop 3.0 band could only be described as a dumpster fire. And thus, as the saying goes: Crap data in, crap data out. No amount of analytical processing could fix the flaming river of bad data into the platform. I talked about this at length in my review, and some 346 comments since then confirmed this by everyone else. Literally, nobody has managed to show me a single good hard/interval/etc workout with accurate comparative HR data. And yes, I’ve actually continued to wear the Whoop 3.0 sensor since my review. And with 379 workouts worth of data in every possible body location, compared to 2-4 other heart rate sensors per workout, and 531 ‘recoveries’. I’m pretty sure nobody has as much comparative data as I do on this thing. Which, means I’ll be well suited to talk about what, if anything, has changed on the 4.0 edition.
Whoop’s new 4.0 sensor is apparently all about improving accuracy of that data (as well as adding more data). We’ll get to those technical bits in a second."