SSH-forwarded X11 display from Linux to Mac lost after some time

The ssh sessions started after I changed the Mac client's /etc/ssh_config to include the line:

ForwardX11Timeout 596h

are all working fine and have been all day. By now they all would have been refusing to start new xterms. So I believe this is the answer, and luckily a simple solution, but the timeout will still happen 3-1/2 weeks from now.

man ssh_config

ForwardX11Trusted

If this option is set to "yes" remote X11 clients will have full access to the original X11 display. If this option is set to "no" remote X11 clients will be considered untrusted and prevented from stealing or tampering with data belonging to trusted X11 clients. Furthermore, the xauth(1) token used for the session will be set to expire after 20 minutes. Remote clients will be refused access after this time. The default is "no" See the X11 SECURITY extension specification for full details on the restrictions imposed on untrusted clients.