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Elan 4.2.1, released by Lean FRO, is a lightweight version manager created specifically for the Lean theorem prover ecosystem; its single purpose is to keep every Lean project on a system running the exact compiler and lake build-tool revision declared in the project's lean-toolchain file. When a user enters a directory that contains such a file, the elan-controlled lean and lake binaries already on the PATH silently detect the requested version, download it if it is missing from the local cache, and then delegate all further commands to the correct toolchain. This behavior makes Elan equally useful for academic researchers who maintain formal proofs across several Lean releases, for instructors who need each student assignment pinned to a different compiler snapshot, and for continuous-integration servers that must switch rapidly between nightly and stable builds. Beyond the automatic mode, the elan executable exposes explicit sub-commands—install, select, run, uninstall—that allow power users to list available Lean versions, pin a global default, spawn a one-off command with an alternate toolchain, or purge obsolete installations to reclaim disk space. The tool is delivered in four published releases so far, culminating in the current 4.2.1 build, and is distributed under a permissive license that encourages both individual and enterprise adoption. Because Elan itself is written in Rust and bundles no external dependencies, it occupies only a few megabytes and adds negligible overhead to each Lean invocation. Elan is available for free on get.nero.com, with downloads provided via trusted Windows package sources such as winget, always delivering the latest version and supporting batch installation of multiple applications.
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