Determinate Systems has released the Magic Nix Cache, a GitHub Action that can significantly accelerate Nix-related workflows. Nix builds can be slow due to the dependency tree realized by Nix, but Nix is good at caching. The Magic Nix Cache, written in Rust, uses a GitHub Actions Cache API, enabling it to cache all Nix store paths automatically, delivering expected benefits without requiring signing up to an external service. The security offered is similar to the Actions Cache API, resulting in cache isolation across different branches and tags. Although not public, it has limited drawbacks and can speed up Nix-related build times by up to 50% without configuration changes.
https://determinate.systems/posts/magic-nix-cache