I finally got round to making the relevant changes to allow the green_light gem to work with Rails 4. This has been long overdue since there are quite a lot of legacy apps making use of it. There is one main difference to take note of in this release, which is the specification of models to validate. Models use to be specified with a yaml configuration file config/green_light.yml, however, now it is done automatically in the initialisation of the Rails engine. One less thing to think about.