Earlier quoted context omitted.
To some degree they have opened the Power9, which is hardware. For hardware it's like leaps and bounds more open than anything else out there that can compete with it. RISC-V is more open, but the hardware isn't necessarily open, and it's not yet really competing at the same scale as Power9 does... yet. There is hope :)
Their open power initiative is really no more "open source" than say Intel's processors, with the possible exception of Management Engine shenanigans from Intel.
It's a lot more open than Intel's. You can get the hardware chip blueprints if you join the foundation.
But the firmware is all Apache 2 licensed.