--- title: Changelog: introducing lazy trees | daily.dev description: Determinate Nix 3.5.2 introduces lazy trees, a long-requested feature that dramatically improves Nix evaluation performance and disk usage. Instead of copying... canonical: https://daily.dev/posts/changelog-introducing-lazy-trees-tkd5dcvo0 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Changelog: introducing lazy trees | daily.dev og:description: Determinate Nix 3.5.2 introduces lazy trees, a long-requested feature that dramatically improves Nix evaluation performance and disk usage. Instead of copying... og:url: https://daily.dev/posts/changelog-introducing-lazy-trees-tkd5dcvo0 og:image: https://api.daily.dev/og/posts/tkd5DCvo0.png og:image:alt: Changelog: introducing lazy trees og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Changelog: introducing lazy trees **[Determinate Systems](https://daily.dev/sources/determinate-systems)** · 6 min read · 0 upvotes · 0 comments ## Summary Determinate Nix 3.5.2 introduces lazy trees, a long-requested feature that dramatically improves Nix evaluation performance and disk usage. Instead of copying entire source trees to the Nix store, lazy trees uses a virtual filesystem to copy only what each expression actually needs. Benchmarks show wall time reductions of 3x or more and disk usage reductions of 20x or more — for example, evaluating a Nixpkgs attribute dropped from 304 MB to 13 MB and from 11 seconds to 3.5 seconds in CI. The feature is opt-in for now and can be enabled via a config flag. A PR to upstream Nix is open. Future improvements include better evaluation caching, parallel evaluation, and multi-threaded flake unpacking. ## Full article daily.dev links to this article rather than hosting it. 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