This is on purpose. We're choosing to it this way for this release - new installs aren't in the beta, but anyone who already agreed to be in the beta (by downloading and installing the pre-release beta) will still be in the beta, unless they remove themselves and then update the client.
We use the beta still before releasing public clients. So if you want to see what's fresh before it goes public, please stay in the beta. Your feedback helps us find and fix problems before public release.
@scottlu Ok, I welcome that change. But in turn, the stable release notes should be displayed once a beta phase has ended and the client is in "stable mode".
Nothing extracted yet.
After the beta was released as stable the client didn't reset to "Not participating". This has worked for previous betas. Additionally, the "Steam Beta Update" is still provided as an option in the preferences.
Besides of being somewhat incorrect and confusing, this also has the side effect of showing the wrong release notes. Instead of showing the newest stable release, the update dialog still shows the announcements of the Steam Client Beta group.