What Is the Difference Between a Source-Breaking and a Binary-Breaking Change in a .NET Library?
A source-breaking change stops consumer code from compiling the next time it is rebuilt; a binary-breaking change makes already-compiled consumers fail at run time with MissingMethodException, MissingFieldException or TypeLoadException. Measured on .NET 10 with a v1/v2 DLL swap, plus what package validation catches and what it misses.