The current Google TPU uses X280
Google looks set to use RISC-V architecture for its future TPU chips aimed at AI computing.
SiFive, which is a developer of commercial RISC-V processors and IP blocks for them based on the RISC-V instruction set architecture, expects to earn from $240 to $280 million in 2024, which is significantly higher than usually. The company's documents do not say anything directly about Google — the company only notes that it has high hopes for the «second generation chip for artificial intelligence servers». The Register resource suggests that the developer is going to license its X390 core to Google, which, in turn, is going to use it to create the next generation TPU.
The point is that Google is already using the SiFive X280 core in its current generation of TPU, that is, for SiFive this will really be the second generation of the chip. It is worth keeping in mind that the X280 core is not the basis of Google chips — it serves only to transfer data to matrix multiplication blocks.