In https://jira.mongodb.org/browse/SPEC-1118 a spec change was made to prohibit passing explicit read concern and write concern to transactions. This spec change is a behavior change for Ruby, and Ruby already implemented transactions by the time the change in 1118 was made, however the 1118 did not spawn a Ruby ticket to implement it. As a result, Ruby is presently not compliant with requirements added in 1118.