After three Boost releases and a year of warning, this is a reminder that Outcome v2.2 is to replace v2.1 as Boost.Outcome. This is a breaking change, all existing Boost.Outcome code shall need to be upgraded as of Boost 1.76 onwards. Changes: https://www.boost.org/doc/libs/1_75_0/libs/outcome/doc/html/changelog/v22.ht... Upgrade guide: https://www.boost.org/doc/libs/1_75_0/libs/outcome/doc/html/changelog/upgrad... You should see the merge land into boostorg/outcome next few days. It'll take some weeks to upgrade the tutorial and documentation. Niall