100x means that I can finish something that would have taken me 10 years in a little over a month.
It would be obvious not because people are posting “I get a 100x productivity boost”, but because show HN would be filled with “look at this database engine I wrote in a month”, and “check out this OS that took me 2 months”.
And people at work would be posting new repos where they completely rewrote entire apps from the ground up to solve annoying tech debt issues.