The ET-based algorithm is a purely a software upgrade. It will definitely be able to run on the current OpenSprinkler 2.3, OSPi and OSBo. It should be compatible with OS 2.0 and 2.2 as well. However, for OS 2.1 we are not quite sure because the software upgrade might require additional flash memory space, which may not be available on OS 2.1 (due to its rather large bootloader).