Which spectral types classify the universe's speed demon stars with the shortest lifespans?

O and B

The stars destined for the shortest, most furious lives are those located at the high-mass, high-temperature end of the stellar classification sequence. Specifically, these stars fall into the O spectral type, which are the hottest and most massive, often followed closely in lifespan by the B-type stars. Because these stars possess enormous gravitational forces, they must maintain extremely high core temperatures and pressures to achieve hydrostatic equilibrium. This intense internal environment forces them to consume their hydrogen fuel at an utterly ferocious rate, causing their main sequence existence to be measured only in millions of years, a cosmic blink when compared to stars like the Sun.