Sorry, I wasn't clear. That's exactly what they do do. These aren't separate APIs; they are modified versions of libc and the STL that speed up the implementation. Facebook apparently has similar STL replacements that they've open-sourced as part of Folly.

(The string utilities I was referring to actually are separate APIs, focused around manipulating string pieces that are backed by buffers owned by other objects. It's like the slice concept in Go or Rust. With the growth in Google's engineering department, it got very difficult to ensure that everybody knew about them and used them correctly; this is probably easier if they're part of the stdlib. Indeed, they're in boost as string_ref, but most of Google's codebase predates boost - indeed, they were added by a Googler.)