Hello,
tl;rd: moat bridges are not distributed anymore. Don't shut them down as they are still used but don't create new bridges with "BridgeDistribution moat".
BridgeDB has being our bridge distribution system since 2007. For years we have being developed a replacement of BridgeDB[0] called rdsys[1]. And finally yesterday we replaced the last distributors missing in rdsys (email, https and moat) and turned off BridgeDB.
The only visible difference is that captchas has disappeared from https://bridges.torproject.org and requesting bridges in Tor Browser gives you a static captcha and doesn't even verify if the answer is correct (until we have the time to update TB to don't request the captcha[2].
The mayor difference for bridge operators is that we don't distribute "moat" bridges anymore. We have merged circumvention settings and moat and now is one distributor handing over "settings" bridges. For now we are going to keep the existing "moat" bridges assigned to "moat" and don't distribute them, so users that have one of those bridges can keep using them without risk of censors finding it.
New bridges will not be assigned automatically the moat distributor, only existing bridges or bridges with "BridgeDistribution moat" will stay in this distributor. We plan to watch the usage of moat bridges and evaluate moving them to another distributor depending on the usage[3].
Thank you for running bridges.
[0] https://gitlab.torproject.org/tpo/anti-censorship/bridgedb/ [1] https://gitlab.torproject.org/tpo/anti-censorship/rdsys/ [2] https://gitlab.torproject.org/tpo/applications/tor-browser/-/issues/42086 [3] https://gitlab.torproject.org/tpo/anti-censorship/rdsys/-/issues/233