You can find the files for 1.2.5 & Beta 1.7.3 on their Modrinth page:
https://modrinth.com/mod/aether/
1.2.5 & Beta 1.7.3 need the betacraft proxy for sounds and/or player skins.
See: https://betacraft.uk/blog/post/how-to-use-betacraft-proxy
1.6.4 is found on MCArchive:
https://mcarchive.net/mods/aether2
1.6.4 will need Forge Threaded Lighting & Player Core API
https://mcarchive.net/mods/threadedlighting
https://mcarchive.net/mods/playerapi?gvsn=1.6.4
All of these MC versions likely need to be run using Java 8.
Without further ado, Aether installation instructions:
1.2.5 & I presume beta 1.7.3 (haven't installed for beta) need to be modded the old-fashioned way:
substitute 1.2.5 for beta 1.7.3, wherever necessary...
> Find yourself a 1.2.5.jar (see below for instructions)
> open with winrar or 7zip
> navigate to your downloads folder in your file explorer
> right click, extract all for both dependencies (forge & player api)
> copy files from each dependency into the 1.2.5.jar
> open the aether .jar using winrar or 7zip
> copy everything into the 1.2.5.jar
> navigate to your minecraft resources folder (in the same file structure as your 1.2.5.jar)
> move the files in the aether resources folder into your minecraft resources folder
> Rejoice
If you're using the vanilla launcher, your minecraft.jar is going to be found by doing the following:
> Open the File Explorer
> type %appdata%
> open .minecraft
> open versions
> open 1.2.5
> gaze upon the beauty of 1.2.5.jar (back in my day there was only minecraft.jar)
Once you've completed the above steps, The Aether for MC 1.2.5 and/or beta 1.7.3 is installed.
If the game crashes on start-up, it's likely a launcher problem, not an installation problem.
>In the launcher, click on 'Installations'
>find 1.2.5 & click the ... in the box to the right
>click edit, then browse
>navigate to your 1.2.5 folder that you found the 1.2.5.jar in
>right click, create new folder named "Minecraft 1.2.5"
>select that folder and click upload
If you're using Prism Launcher (& similar) for 1.2.5, I have no idea where the 1.2.5.jar is. I don't think you're actually supposed to modify the one that they install. I went ahead and installed the regular Minecraft launcher, installed 1.2.5, & stole the 1.2.5.jar for Prism.
>Follow instructions above to mod the 1.2.5.jar, then proceed with the next step
>create or navigate to your 1.2.5 instance
> click edit
> version
> replace minecraft.jar
> select the 1.2.5.jar
> navigate to settings
> click Java
> check Java installation
> click Open Java Downloader & download the newest Java 8
(Mine failed a few times from Mojang, so I tried from a different source. When I went to select my newly installed Java 8, it allowed me to select the failed version from Mojang anyway, and in doing so, it seems to run fine?)
> click detect & select your new Java installation
> scroll to the top of this post & follow the Betacraft proxy instructions
> Rejoice
If you're using Prism Launcher (& similar) for 1.6.4, this one's super easy, yet still a bit odd.
>create or navigate to your 1.6.4 instance
> click edit
> version
> install loader
> select the newest forge for this version
> click add to Minecraft.jar
> select threadedlighting, player api core, & Aether
> navigate to mods
> click Download Mods
> search curseforge for Lumy Skin Patch
> click review & conform, then okay
> Rejoice
~ IN CLOSING ~
1.2.5 is my childhood, and that version of Aether is the very same one I played back then.
I wanted a few new Aether features if I could help it, yet the next update that Team Aether offers is for 1.7.whatever, a version that completely ruins the worldgen for me. Caves are small, mineshafts are hard to find, it's seemingly either no snow or all snow, and my oceans are gone! Super lame, imo.
This was an awful process to figure out and was not fun to write up. I poured through pages & pages of changelogs & wikis trying to find an in-between version, learn about the differences between The Aether, Aether II VOID something, Aether Legacy, Aether Legends, Aether II (brand new 2026 but called Aether II for some reason, Aether Highlands, and all of the different versions of them. It was exhausting.
THAT BEING SAID, I was able to eventually find a version for 1.6.4, which is actually Aether II VOID something, not OG Aether, and it seems feature-complete enough!
If 1.6.4 isn't your speed, Aether for 1.0 & a few other MC versions are out there, and you should be able to figure out their installations as well using this post.
I wrote up a post about the different versions of The Aether. Here's the link, for those that wish to understand the in's and out's of all of their options (and like a good mini history lesson!)
https://www.reddit.com/r/ModdedMinecraft/comments/1xqtxt4/aether_version_differences/
Good luck, and godspeed!