This is an incremental release with no new features or API breaking changes.
The major version bump originates from the fact that mp++ now requires FLINT>=3 if the (optional) Arb support is enabled. Arb has been incorporated in the FLINT library beginning from version 3 and as a consequence FLINT<3 is not supported any more by mp++.
Additionally, Python interoperability support for Python 2 has been dropped and mp++ now requires CMake>=3.12 when building from source.
The full changelog, as usual, is available here: