The read/write concern spec defines wtimeoutMS to be a 64 bit integer, but it is implemented as an int32_t in libmongoc. (see mongo_write_concern_(get|set)_wtimeout) For full spec compliance, there should be api for setting and retrieving wtimeoutMS as an int64_t.

Currently, drivers that wrap libmongoc have no way of supporting 64-bit wtimeoutMS, so they in turn are also not spec compliant.