As we reported before, Miitomo was taken offline today to update it to the new version. Nintendo has added quite a few new improvements to the app, which is now available for free. The update details are:
As of this posting the app was still undergoing maintenance. So, you are able to update to the new version right now, but you may run into problems trying to play it until after the maintenance period, which is scheduled to be complete by 9 pm PT / 11 pm CT / 12 am ET.