What is the difference in 7800 and 7801

[Satellite]

Did Shimano do some kind of revision and if so what was it?

[victoryfactory]

I don't think even the big "S" knows.

One thing though... the 7801 chain is an incremental "upgrade"
to the point that Shimano sez you can't use the 7800 pins in the 7801
chain.

VF

[RudAwkning]

I believe the 7801 also had the revised crankset with the pin on the plastic "E" shaped clip for the non driveside crankarm.

[Volant]

Fixed the loosening/rattle in the brifters.