Eigen 5.0 Released (gitlab.com)

Eigen 5.0 is out, bringing broad API cleanup, performance fixes and a number of breaking changes that will affect users and downstream ML/linear-algebra projects. This release is the last major version to support C++14 (5.x requires at least C++14; future master will move to C++17), and Eigen has adopted semantic versioning (MAJOR.MINOR.PATCH). The CMake build system was modernized, LGPL-licensed code (e.g., constrained conjugate gradient) was removed, and a set of public API/behavior changes were introduced to reduce name clashes and unsafe practices. Key technical changes to watch for: names Eigen::all and Eigen::last moved to Eigen::placeholders::all/last; direct inclusion of internal headers (../src/..) now fails compilation; runtime SVD thin/full U/V options are deprecated in favor of compile-time choices; BLAS wrappers now return void (not int); Eigen::aligned_allocator no longer inherits std::allocator; scalar comparison masks now use Scalar(1) to avoid UB; Euler-angle outputs and the RNG were changed and can alter numerical results. Practically, expect to update build flags (-std=c++14 or later), CMake targets, third-party integrations, and test suites for potential behavioral differences in random numbers, SVD behavior and angle representations. The switch to semantic versioning should make future breaking changes easier to track.