"Piotr Krzyzowski achieved an impressive double ascent of Lhotse and Everest in Nepal: The Polish mountaineer climbed the two 8000-meter peaks alone and without artificial oxygen in less than 48 hours.
Piotr Krzyzowski stood with Lhotse and Everest a few days ago on his sixth and seventh eight-thousanders. This achievement is impressive in that, unlike most commercial expedition participants on site, the 45-year-old Pole climbed the two 8000-meter peaks alone, without a Sherpa companion and without bottled oxygen. It took him less than 48 hours to complete his double ascent."
Link:
https://www.lacrux.com/en/alpinism/Piotr-Krzyzowski-climbs-Lhotse-and-Everest-without-artificial-oxygen/