Haelian published a video a week or so ago setting out the probabilities for why it was so unlikely that this difficulty configuration would ever be beat: https://youtu.be/S-VUzcJHWF0

Which of course was taken as a challenge, with runner Jade clearing heat 64 yesterday, using an unseeded and unmodded run: https://youtu.be/0mo-kXjasZs

(For context, the seed is the way a particular run is generated, and players can meticulously generate seeded runs to ensure certain things do or don't spawn by taking very specific sets of actions. Dying and respawning - rather then reloading from the menu, which is quicker - resets the seed. That's why challenge runs always start with a death and respawn to show that a pre-configured seed isn't being carried over from previous runs.)

Here's Haelian's reaction to the whole situation: https://youtu.be/5L7_3MrG_08

Insanely impressive, and I don't know if we'll get to see it again.