Dear Maintainer, your package depends on libeigen3-dev. The upstream released a new major version of this mathematical library, 5.0.0. Some basic information about new features and changes in this version can be found here: https://libeigen.gitlab.io/releases/5.0/ This is a major version change and may require code changes in packages depending on eigen3. The key breaking changes include: - Minimum required C++ standard is now C++14 - Changes in the build system integration - Some API name changes sopt FTBFS with libeigen3-dev 5.0.1. The full build log is available at: https://debusine.debian.net/debian/developers-gladk-eigen3/artifact/3761812/ Here is the most probably relevant part of the failing build log: =========================================== common_mpi_catch_main.cc.o -c /build/reproducible-path/sopt-5.0.1+dfsg/cpp/tests/common_mpi_catch_main.cc In file included from /build/reproducible-path/sopt-5.0.1+dfsg/cpp/sopt/../sopt/wavelets/wavelets.h:5, from /build/reproducible-path/sopt-5.0.1+dfsg/cpp/sopt/wavelets/wavelets.cc:1: /build/reproducible-path/sopt-5.0.1+dfsg/cpp/sopt/../sopt/types.h:7:10: fatal error: Eigen/Core: No such file or directory 7 | #include <Eigen/Core> | ^~~~~~~~~~~~ compilation terminated. make[3]: *** [cpp/sopt/CMakeFiles/sopt.dir/build.make:96: cpp/sopt/CMakeFiles/sopt.dir/wavelets/wavelets.cc.o] Error 1 make[3]: *** Waiting for unfinished jobs.... =========================================== libeigen3-dev_5.0.1-1 is available in experimental. When this package version lands into unstable (probably at the beginning of June 2026), this bug will be increased in severity to serious. Thanks, Anton