Definitely not. This change, as I see it, has nothing to do with performance increases (except those that come with the new version of Spider Monkey). The reasons I see for going to c++11: Because we use c++03, and c++11 is the next version of the standard. It's been a few years, the language is widely supported now, and has shown itself to be a major advancement. For instance, any team that's still using RCS should probably consider moving to a newer VCS just because RCS is old and has been greatly improved. It's not the *best* tool for *any* job, and is in So that we can take on the new version of Spider Monkey. If Spider Monkey went Clang-only, we would have to consider more closely, but c++11 is an obvious place to go from where we are (c++03). C++ has loads of new features that are very useful to us covering usability: lambda statements, universal initialization, auto, "for-each" for loop syntax; optimizations: move semantics (including "perfect forwarding"), right-hand references, "standard" threading support (this may not be an optimization over pthreads, but I think it's good); and other functionality: POD types expanded, random number generation is improved. [EDIT] Oh yeah, c++11 is largely (completely?) backward compatible. Compiling a c++03 program as c++11 should have no problems, and any new warnings that show up will only serve to improve the code.