For anybody wondering the P670s are advertised to be around Cortex-A78 performance, their slides 5% slower on SpecINT2k6, but 50% less area) [0] and have 128 bit vector registers.

The X280s are more of an external accelerator with 512 bit wide vector registers and an integrated TPU using Sifives VCIX interface [1]. It enables custom vector coprocessors, in this case a TPU, to interface directly with the vector register file.

The X280s will very likely not run the same OS as the main P670s because of their different VLEN, which would't allow for moving processes between them.

[0] https://www.youtube.com/watch?v=C4DcZyB6i1E [1] https://www.youtube.com/watch?v=si5w7JQtSDk