Nintendo has made a point of designing their new consoles and handhelds to be backwards compatible with older systems in recent years, but a report from Eurogamer back in July indicated that the mysterious NX (now officially revealed as Nintendo Switch) would not be backwards compatible with 3DS or Wii U. The preview trailer for Nintendo Switch confirmed that it uses cartridges, but they do not appear to be the same size as 3DS cartridges, and no disc drive was seen.
Following the upcoming hybrid console’s reveal, popular Japanese publication Famitsu reached out to Nintendo for comment on Nintendo Switch’s compatibility with other devices, and Nintendo confirmed that it won’t be able to play 3DS cartridges or Wii U discs. It’s possible that some sort of digital backwards compatibility could still occur via linked Nintendo Network IDs, but no such feature has been hinted at by Nintendo at this time.
Famitsu also asked about the possibility of Nintendo Switch playing mobile games (which earlier reports indicated), but the answer was less clear for this question. Nintendo chose not to take a hard stance either way, simply stating that they “can’t comment now” on that topic.