Fully custom OS apparently: http://www.theverge.com/2016/10/20/13346004/nintendo-took-the-guts-from-the-nvidia-shield-for-its-new-console http://www.theverge.c

Fully custom OS apparently: http://www.theverge.com/2016/10/20/13346004/nintendo-took-the-guts-from-the-nvidia-shield-for-its-new-console http://www.theverge.com/2016/10/20/13346004/nintendo-took-th... Though I believe the Shield uses a form of Android, and the Switch uses a lot of Shield components so it's plausible that the Switch OS is similar to Android