Dear Richard,
no, 6.18 is not yet released, I just built Csound from the sources on Ubuntu here, using the csound6-branch on git:
janjacobhofmann@janjacobhofmann-ThinkPad-T430:~$ csound --version
--Csound version 6.18 (double samples) May 30 2022
Best,
Jan Jacob
sound | movement | object | space
sonic architecture | site: http://www.sonicarchitecture.de
spatial electronic composition | higher order ambisonic music