C11 In GCC?
Answer : The standard C11 header for threading is <threads.h> , not <thread.h> . See section 7.26 of the N1570 draft. Most of the C standard library, including stdio for example, is not included in the gcc distribution. Instead, gcc depends on whatever runtime library is provided by the operating system. That generally includes both the headers (like <threads.h> ) and the actual code that implements the library. For most Linux systems (or GNU/Linux if you prefer), the library is GNU's glibc; for other systems it will be something else. So the real question is probably when glibc, or whichever C library you're using, will support C11's threading features. glibc adds support for C11 threads in version 2.28. Ubuntu 18.04.1 LTS system currently still uses glibc 2.27. Again, this applies only to implementations using GNU libc, not to all gcc-based implementations. Mentioned by WorldSEnder in a comment. UPDATE: Ubuntu 18.10 (not an LTS (Long Term Su...