Can I use leaded glass for tall window in stairwell?
https://homeguides.sfgate.com/building-codes-tempered-glass-close-stairs-102700.html

"The code makes an exception for any glazing that meets these stipulations but is protected by a horizontal rail on the accessible side of the glass. The rail must be positioned between 34 and 38 inches above the walking surface and capable of withstanding 50 pounds of force per foot without touching the glass."

So, you take your stained glass window and protect it with a railing, and you're now code-compliant. (Check the actual code first instead of trusting the Internet, though.)