It's defeating all 6 monthly bosses in one go. Only paragons will get it for high tier rewards after 100% monthly at TB difficulty.
They're probably talking about the Paragon Gauntlet, which will be a monthly quest Paragon players get access to after fully exploring the TB EQ. I believe all we know so far is that it'll have 6 fights, which will just be the same bosses from each quest in the EQ. Pretty sure it starts next month, so it'll have Gladiator and the other champion release as the last 2 fights.Either that or they're talking about the Grandmasters Gauntlet which is a piece of content you unlock after Act 6