That in Tales of the Jedi: Golden Age of the Sith, the Jedi use corded lightsabers and the Sith don’t use lightsabers at all. Before Golden Age, it was implied that lightsabers hadn’t changed since before the formation of the Sith (it was later made clear both sides did in fact already have modern lightsabers at the time).
That the formation of the Sith was moved from 25,000 years before the movies to 7000 years before the movies. Sith characters in Golden Age of the Sith think that the existence of the Republic is “just a myth”, a bunch of lore had been written and characters created with 25,000 years in mind, and Golden Age refers to the formation of the Sith as the “First Great Schism”.