As discussed at the confab, we should use the version available with the Ubuntu Long-Term-Support distribution at the time of the release (this will be 18.04 - Bionic Beaver). This version is currently CMake 3.9.5. It may change in the future. Since Windows developers download the latest version from cmake.org and macOS developers download from cmake.org or use Homebrew (which tracks latest CMake), there is not a reason to use a lower version in these cases.