"In this context, the “8th generation” refers to seven generations of the traditional MIPS architecture, followed by an upcoming RISC-V design. It sounds like the company is implying that this is a smooth transition with some level of compatibility between the old and the new. It isn’t. It’s a clean break as the company switches from the old CPU design, that it owned, to a new one that’s in the public domain."
Mips R6 (Warrior m62xx/i6400/i6500/p6600) was already somewhat incompatible with R5 and earlier, the seventh generation nanomips i7200 was incompatible with that again.