You can pin a gem to a specific version, of course.

`gem "mygem"` installs the latest version. `gem "mygem", "~> 4.0.0"` installs >= 4.0.0 but < 4.1.0, which is what you probably want when using Semantic Versioning, which most gems adhere to, to get the latest patch version. `gem "mygem", "4.0.10"` installs exactly that version.

Well, don’t use this then. It’s a neat feature for quickly iterating, and you can quite easily go up from here to a proper Gemfile/Gemfile.lock.