4.0.1

Version 4.0.1 (November 11, 2026)

Compiler

1. 21a076966 Added mjs_getInStringVec to read entries from an mjStringVec by index.

Python bindings

2. a937a4f91 Enabled the MuJoCo Studio Web Viewer (mujoco-studio --gfx=web and
   mujoco.studio.launch_web) on Windows by shipping the precompiled browser client in a platform-independent
   mujoco-studio-wasm wheel installed automatically by mujoco-studio.

Bug fixes

3. 9ae9bad01 Fixed a bug in the sparse Cholesky factorization introduced in 4.0.0, which merged rows with
   different descendants into one supernode and gave the Newton solver a wrong Hessian factor when the constraint
   Jacobian is sparse, causing slow convergence, wrong accelerations and divergence (#3767).

4. 144ede984 mj_loadAllPluginLibraries now skips a dynamic library that fails to load with a warning
   instead of calling mju_error, so one unloadable library in the plugin directory no longer aborts
   simulate at startup. In the 4.0.0 macOS and Linux archives this happened with the USD decoder
   plugin, which can only be loaded from a Python process.

5. 409f981ab Fixed issues in single-shot multicontact for cylinder edge collisions
   (#3748, #3752).