The release candidates for the first 1.73.0 beta release are now available at:
    https://dl.bintray.com/boostorg/beta/1.73.0.beta.1/source/

The release notes are not yet available.

The SHA256 checksums are as follows:
44f323b42c4375ab3751b67ac5ce53ba5267af20cf375be75675d8952d3cca4e  ./boost_1_73_0_b1_rc1.7z
5270fa89243a3508331bd3773800de6d2f98d1f160b95e362fa8269d9cd58773  ./boost_1_73_0_b1_rc1.tar.bz2
82ffcd4a2e558a31f1ddd6a54ef6c00dae28b95c2ddee575c285544085dcb004  ./boost_1_73_0_b1_rc1.tar.gz
910b7560ee239472cc69e6a0c680dc4d9d7ea234faad807738ec98e4811c63d4  ./boost_1_73_0_b1_rc1.zip

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.