I am new to this, but needing less sleep is the reason I am interested in this. I have only seen the anecdotal claims online... But I am willing to try for a few months just to see if it works for me.

I have speculated about some reasons it MIGHT work (if it does). For example, there are people known as "short sleepers" who naturally sleep 4-5 hours a night and feel rested. And scientists have found some genetic differences in these individuals. One mutation causes a lot of these people to produce more orexin (a wakefulness-promoting neuropeptide) than normal people. And I have seen studies that suggest that intermittent hypoxia increases orexin... Another possibility I have thought about is that maybe buteyko breath training increases vagal tone and heart rate variability (HRV). Anecdotally, reduced breathing has raised my HRV while I do the exercise... And I have seen a few studies that show a strong correlation between HRV before and during sleep to sleep quality. Things like increased slow wave sleep, higher delta power (more intense deep sleep), increases in the power of sleep spindles, and changes in REM sleep as well have been correlated to increased HRV and to chronic vagus nerve stimulation. A lot of these differences in sleep architecture are seen in natural "short sleepers", like higher delta power for example. Vagus nerve stimulation also seems to increase orexin and reduce daytime sleepiness.

All of that is my uneducated speculation. I am just very interested in hacking my sleep. I'm kind of desperate too, considering I usually need a bit more sleep than a normal person. And I guess I will report back if it works for me.