Hi Martin Kouba. From what I understand (I'm not a glassfish developer), the max-sessions setting puts a maximum cap on the number of sessions the server will allow to be active at any given point in time. With the older version of WELD, when this number of sessions are exceeded, the server will return back a message for new http sessions saying the max number of sessions were exceeded, I believe with the HTTP status code 503. We considered using this as a crude safeguard against too many sessions on our web server but decided against it for now, it could be useful in the future.