Market share table:

Here is how Hyperion Research carved up the on premises HPC server market for 2023, including a revision that brought in HPC machines made by Supermicro and other non-traditional suppliers:

Those non-traditional suppliers, who are by and large building “AI supercomputers,” as a group have a little more than a quarter of the market, and HPE has the dominant market share at just a little under a quarter – thanks in large part to the massive deals taken down by Cray to build pre-exascale systems in the United States and Europe and exascale machines in the United States.