That’s right: GameCube controllers are now compatible with the Nintendo Switch. Although there has not been an official announcement yet, fans have discovered that the latest Switch update has made it possible to use GameCube controllers with the Switch, via the WiiU GameCube controller adapter.
The adapter is no longer produced by Nintendo, but can still be found used or new online and at physical retailers fairly easily. The adapter can be plugged into the Switch dock’s USB ports. You’ll also have to check your system settings on the Switch and make sure wired controllers are allowed. Holding down L and R on the controller will pair it to your Switch.
Be warned: the Gamecube controllers do have a different button scheme than the Joy-Cons, so some Switch games may not work perfectly with the classic controllers. There is also no home button, so getting out of a game back to the main screen may be a slight hassle.
For a while during the WiiU’s life, Nintendo produced GameCube-style controllers for the WiiU; it’s possible that Nintendo may have a similar product lined up for the Switch, modified to accommodate the differing buttons. It’s also possible that Nintendo is readying some GameCube games for the Eshop, specifically Smash Bros.