An important note is that while this might be the first PRESTO equipped agency taking open payments, it is not a PRESTO installation. Ottawa owns their own equipment and already runs a shadow fare system for bus transfers, train tickets, multi-day disposable RFID passes and accessibility/employee/retiree/contractor cards, as well as being compatible with STO's MULTI. Though this readers on the buses predate this internal system, they have been upgraded over the past year to enable it. This is the layer that open payments will run at, separate from PRESTO. They worked with Scheidt & Bachmann, the manufacturer of their equipment, to enable this functionality.
Though TTC also uses S&B equipment, it is owned by Metrolinx, so they have less flexibility. GRT relies fully on S&B for their system, so it will be interesting to see if they can leverage OC Transpo's work into their own system.