Until the December 2013 timetable change, the S1 continued east from St. Gallen to Altstätten SG, on the Chur–Rorschach line. The service was truncated when the Rheintal-Express [de] was extended west from St. Gallen to Wil.[7] With the December 2018 change the S1 began running half-hourly and InterRegio 13 replaced the Rheintal-Express.[8]
Between the December 2018 and December 2021 timetable changes the S1 operated every half-hour between Wil and St. Gallen, continuing from St. Gallen to Schaffhausen as the S8.[5] With the December 2021 timetable change, the entire Wil–St. Gallen–Schaffhausen route was designated as the S1, albeit with the timetable color formerly associated with the S8.[9]