Unfortunately, people found a few problems in the RC1 (Thanks to everyone who tried it, and especially to those who reported problems) We now have a RC2, available at: https://boostorg.jfrog.io/artifactory/main/beta/1.81.0.beta1/source/ The SHA256 checksums are as follows: bff5cf561ab65be658c030f6b348a4907cce039611e96112dc8f6e27b6a9f44b boost_1_81_0_b1_rc2.7z 7f300d48189b9f25bf3b214168912043681819f0ace332b0e9de503f7e23e72c boost_1_81_0_b1_rc2.tar.bz2 1619545e2f180caf6615eb83220ebcc1342c20704307b59871d987b95adb1326 boost_1_81_0_b1_rc2.tar.gz 3f9ebb8b23cab1617a7ae9a38b251e4803c917832b0c4c96b907cf122dec428f boost_1_81_0_b1_rc2.zip The changes are: 1) Fixed a compile error in Boost.ASIO 2) Fixed several compilation errors on Mac OS with libstdc++. (Boost.Config) 3) Fixed Boost.JSON compilation error with X11 4) Fixed a crashing but on shared_ptr on PPC (Boost.Sharedptr, Boost.Align) As always, the release managers would appreciate it if you download the candidate of your choice and give building it a try. Please report both success and failure, and anything else that is noteworthy. -- The Release Managers