As you may know, we have had people busy looking at what it takes to make our packages reproducible.
There has been a lot of progress there lately. Our reproducible builds team (along with the wider reproducible builds community) has been building our packages in different environments to test how stable the builds are . The good news is that >80% of our packages could be built twice in varying environments and give the exact same result.
However, that is only part of the picture. Ideally, we want people to be able to take one of our packages and rebuild it exactly. With the release of pacman-5.2, packages record a lot more information about their build environment. That means we can reconstruct a package's build chroot, and then rebuild it. There are two tools in the works to do this. One by Morton (Foxboron)  and one by Eli . Note that both tools need more testing to be ready for a wider release and currently require some manual editing to run.
The good news is, we have at least 10 packages that can be precisely reproduced using both these tools ! This means you can take one of these tools and rebuild a package from the repos, and get the exact same package out of it. This is an amazing effort - well done to the team!
To keep this momentum going, it would be great to rebuild every package in [core] using makepkg from pacman-5.2+. That way we can test which packages are actually reproducible and work towards fixing those that are not. So be prepared for almost the entire repo to hit [testing] soon, and get your sign-off shoes on!
Again, a huge congrats to our reproducible builds team. This has been a massive amount of work!
 https://tests.reproducible-builds.org/archlinux/archlinux.html  https://github.com/archlinux/archlinux-repro  https://github.com/eli-schwartz/devtools/blob/reproducible/makerepropkg.in  https://wiki.archlinux.org/index.php/DeveloperWiki:ReproduciblePackages