Eigen 5.0.0 (gitlab.com)

Eigen 5.0.0 is a major release with broad API, performance and infrastructure updates across Eigen’s template expression and linear-algebra core. It introduces semantic versioning (MAJOR.MINOR.PATCH) while retaining a legacy “WORLD” number for posterity, and is the last major release supporting C++14—future master branches will require C++17. The release modernizes CMake, removes older properties, strips LGPL-licensed unsupported code (e.g., Constrained Conjugate Gradient), and tightens encapsulation (direct inclusion of internal ../src headers now causes compile errors). For ML and scientific codebases that depend on Eigen, several compatibility and behavioral changes are important: namespace conflicts moved Eigen::all and Eigen::last to Eigen::placeholders::all/last; runtime SVD thin/full options are deprecated in favor of compile-time choices; BLAS wrappers now return void for compatibility; Eigen::aligned_allocator no longer inherits std::allocator; scalar comparisons produce masks with Scalar(1) rather than bit-patterns; Euler-angle outputs and Eigen’s RNG have changed (don’t rely on exact random sequences or prior Euler representations). Practically, expect build updates (use -std=c++14+ for 5.x, plan for C++17 later), CMake tweaks, and small API/behavioral fixes when upgrading libraries and ML frameworks that embed Eigen.