Arnold Kim, MacRumors:

The benchmarks confirm that the new ‌MacBook Air‌ SSD is approximately twice as fast as the previous model with 2190 MB/s writes and 2675 MB/s reads.

As promised by Apple, here:

The M1 chip’s storage controller and latest flash technology deliver up to 2x faster SSD performance

Apple promised a lot with these M1 chips, but everything I’ve read shows they’ve delivered on those promises. This is a major step forward.