It's Gen 9.
Wii U was 2012
PS4 and X1 were 2013.
That is Gen 8.
Switch is 2017 which is 5 years after the Wii U and 4 years after the PS4/X1.
And if the PS5/X2 launches in 2020 then it'll be 3 years after the Switch, if either gets an early start in 2019 then it'd be 2 years after.
Nintendo just got out even earlier this time in the new generation since the Wii U was such an abysmal failure.