Vstdlib_s.dll file is part of vstdlib_ s.dll product developed by Steam. It is responsible for Valve Corporation functionality. This part is required for vstdlib_ s.dll to function. If you are planning on replacing vstdlib_s.dll with a new version make sure that you backup your old file. Replacing vstdlib_s.dll file with a diffent version can cause vstdlib_ s.dll to malfunction.