It’s inconsistent. Canonically in most Trek warp 10 asymptotically approaches infinity, which is why you see a lot of nine-point-nine-something when really high speeds come up, but every now and then the writers forget and you’ll hear about exceeding warp 10.
You also have things like transwarp, quantum slipstream, or the proto-drive which operate on different principles and don’t follow the warp curve. Their equivalent warp factors would just involve stacking up ever more 9s after the decimal point, but their speeds aren’t typically expressed in terms of warp.
It’s inconsistent. Canonically in most Trek warp 10 asymptotically approaches infinity, which is why you see a lot of nine-point-nine-something when really high speeds come up, but every now and then the writers forget and you’ll hear about exceeding warp 10.
You also have things like transwarp, quantum slipstream, or the proto-drive which operate on different principles and don’t follow the warp curve. Their equivalent warp factors would just involve stacking up ever more 9s after the decimal point, but their speeds aren’t typically expressed in terms of warp.