It is my pleasure to announce that development builds for the Minecraft 1.13 release are now available. I will outline important considerations/changes below, but it is important that you read this post in its entirety, including the original 1.13-pre7 section. Even if you have already read that part, please read it again as it is still very much applicable.
In terms of server preparation, we have now added 1.13 to the "Tested Minecraft Versions" resource field, as well as created a new field called "Native Minecraft Version". This second field has two choices - "Legacy (<1.13)" and "1.13". If you are a developer you should please set this field to indicate what api-version you used to program your plugin, as it will no doubt be an important consideration for server owners looking to update.
As for general server stability we expect that this update will fall into three key "waves" for those looking to update. We are currently in the extreme caution wave and expect to advance through them as 1.13.x versions are released by Mojang.
Extreme Caution (1.13 - Current): This version is stable for those looking to run a public server based on Minecraft 1.13, but only if an entire reset of all worlds and data is performed, and all plugins in use have a Native Minecraft Version of 1.13. It is not safe to use on existing worlds. There are known Vanilla bugs that will irreparably delete data from your old world, or otherwise render it unusable. You may use this version to test conversion of your world, but you will NEED to restore your world from a 1.12.2 backup before moving onto the second wave.