It's 4% for 30 years from a 60/40, stock/fixed income portfolio if you want to survive the 1929 stock market crash and Great Depression, or the high inflation of the 1970s and 80s.

Correction:
It WAS 4% for 30 years from a 60/40, stock/fixed income portfolio if you want to survive the 1929 stock market crash and Great Depression, or the high inflation of the 1970s and 80s.

It might be so in future as well, PROVIDED that real stock and bond yields on retirement date are comparable to the situation at the start of that historical period being examined. Which they aren't.

The sustainability of a portfolio and any withdrawal scheme is not a function of what was observed in the past, it's a function of the real future net earnings yields of the portfolio in question. Those can be approximated using the expected real bond yields and CAPE ratio at the start date. If real bond rates are low and CAPE high, success stories from the deep past should be of no comfort at all to those tempted to thing historical results are predictive.

You don't want to be in the position of a person who reasons thusly: "That guy bet on coin flips and won half the time, so I'll get the same win rate buying lottery tickets". Wagers with different odds get a different spread of outcomes.

Jim