The STM has this in their schedule to update the GTFS, it doesn’t mean it’s the date of the REM opening. You can see the calendar of when STM updates their routes on their GTFS page:
The schedules 2026 will change on the following dates:
January 5, March 23, June 15, August 24 and October 26The GTFS data are usually available 10 days before the schedule change .