It's confusing that RISC-V is so often described as "open source". The specs (ISA + extensions) are open and free from patents (at least as far as we know). While there are a large number of open source implementations available, many of these, however, implement only a simple microcontroller-style RV32I core.

The cores available in "large" physical chips you can buy today (XuanTie C906 on the Allwinner D1 SoC, SiFive U54/74 e.g. on the BeagleV and HiFive Unmatched) are proprietary. I think one of the few companies that open sourced their commercially used cores is Western Digital ("swerv" cores - https://github.com/westerndigitalcorporation/swerv_eh1), but these are also RV32I microcontroller-class CPUs.