Patching, there's generally a <5MB patch after each maintenance. As far as I know there have not been any patchnotes since closed beta, but some changes will be obvious to you (battle errors, loot lag etc have been fixed through these small patches so far).
It depends on what they change but there generally are patch notes e.g:
Sept 9th Maint&Update wrote:
[Important Update Details]
- An issue which caused players to, if they had changed equipment immediately after performing a “stand up” emote from a chair, warp to the location where their last “stand up” emote was performed upon selecting the emote again has been addressed.
- Server settings have been adjusted.
Whenever they have a patch following maint, not always but generally when it's something of that nature or other gameplay relations they announce it.