The PCB design is available at the bottom of the page here: https://chi.bio/forums/topic/pcb-source-files-and-changelog/
It doesn’t have a changelog explicitly, I think the major change for V1.3 was removing a “I2C extender” chip that was between reactor->pumps because it seemed to be achieving the opposite (less reliable signalling).
Thanks for the response Harrison. I think you linked to this forum post though. Also, just to avoid confusion, I’m hoping to access the PCB project files (KiCAD, Eagle, etc), not just the production files (Gerbers).