First, great work on formatxx and thanks for kind words about the fmt library (previously cppformat)! Just wanted to give you a quick update and point out that in the recent versions of the library the part

the compilation time overhead of including its primary header is pretty large, and its support for formatting user-defined types relies on std::ostream wrappers (which are neither lightweight includes nor are they runtime efficient)

no longer applies because the ostream support has been moved to a separate header and the most heavy includes have been removed. There are still some non-essential headers included such as vector and utility which I plan to get rid of in the next release but I doubt they add much to the compile time. There has also been substantial compile-time speed optimization work as part of fmtlib/fmt#243.

Could you by any chance update the README file?