I unplugged it the week after I got it out of curiosity. Here's some anecdotal evidence:
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I had about 18h of screen time during that period, but all lightweight stuff (I work on another MacBook on workdays). So very good battery life in that use case.
For heavy stuff, you can still drain the battery in under 4h. Something funny about it: since the fans almost never spin up into audible levels, you can drain the battery very fast without realising that the task you're running is heavy. For example, the day I got it I had to compile a lot of source to get all the Python packages I use (NumPy, SciPy, Numba & NetworkX) to work on the same Python version. And while doing it, the battery was draining fast (~15%/hour). I was a bit concerned, but then I opened the Activity Monitor and realised I was using all cores at max. And then I remembered, when I did the exact same thing on the i9 MBP, the fans were so loud that I plugged it in because I didn't expect the battery to last long. On the M1 Pro, I didn't even realize the task was very CPU intensive until I saw the battery draining.