https://www.gamespot.com/articles/nintendo-switchs-paid-online-service-launching-in-/1100-6456485/

The Nintendo Switch's paid online service will launch in September 2018, Nintendo president Tatsumi Kimishima confirmed today during an earnings call.

Online play for Switch games has been free since the system launched in March 2017. Initially, Nintendo planned to launch its paid service in Fall 2017, but it was delayed to 2018. At the time, Nintendo announced it would offer memberships for 1 month ($4), 3 months ($8), and 12 months ($20), but it remains to be seen if those prices are still accurate.