Where to Download
Changes
Below are the major changes of the released versions and links to more detailed release notes.
Alpha
This third alpha release (0.4.9.3-alpha) introduces the new CGO circuit cryptography from proposal 359 bringing better security.
It also contains several TLS related minor bug fixes detailed in the release notes below.
This will very likely be the last alpha before the first 0.4.9.x stable release which will bring Happy Families and the aforementioned CGO cryptography.
Release Notes
Stable
As for the new stable 0.4.8.18, an important bug fix for onion service directory is being released along several other minor bugfixes for other subsystems.
As always, please upgrade as soon as possible. Thanks to our beloved relay operators and everyone else! 
Extra note about the 0.4.8.x series
Since version 0.4.8.17, if OpenSSL 3.5 is present on your system, Tor will attempt to use the MLKEM-768 cipher, which is quantum-resistant. As more and more relays adopt this support, the entire network will gradually move toward being post-quantum safe at the transport layer (TLS). If you are able to setup your system with this, that would be great! Thank you!