No. It is part of the proprietary Windows SDK. However, Microsoft has shared source code for some CRT components via GitHub (Microsoft/STL), but corecrt.h remains a system header.
Here is the hard truth: corecrt.h is not a standalone file. It is a critical, internal component of the . Treating it like a loose file to download is a recipe for linker nightmares, system instability, and potential security vulnerabilities. corecrt.h download