Release Environment Versioning
Explains how Release versions environments.
Release creates a version string for all of your environments. It consists of the version of your default config + the version of your environment-specific config. The environment version looks like this: v2.4. We think of the defaults version being the "major" version number and the environment-specific versions being the "minor" version number. You can see this version string in a number of places which we'll go through below.

Default Config Version

The default environment configuration's version is the first number following the v. Whenever you save either the environment configuration or the environment variables the major number will increment. When you view a particular environment it will be the first part (or the "major number") of the overall version string.
This the current default configuration version under settings

Environment Specific Version

The overall version for an environment is concatenation of the default config version that your specific version based on, and the currently deployed version of the specific configuration. The version appears in a few different places in the environments section:
On the environments screen
On each environment details screeen
When you click into an environment and view its details you will see two versions that may or may not be the same. Whenever you save the configuration or the environment variables for the environment (this is the same for the default config and default environment variables too), Release will increment the minor version number and show you that you haven't deployed the latest configuration.
You must click the "Apply" button to (re)build your environment with the latest configuration version.
Currently Deployed v1.4, but v1.5 is available
Once you have created an environment the leading part of the major version vX.Y (the X in this example) is from the default configuration that your specific configuration started out originally. This will NOT change. Release does not merge changes to the defaults into the specific config of an existing environment.
For example, if you have an environment with a version v1.4 and you create version 2 of the default config, all new environments will be based on the major version 2 of the default config, but your environment that was based on the major version 1 will stay on that major version v1.4. If you make changes to that specific config, then the minor version will change from v1.4 to v1.5, not v2.Y.