Incorporating an app version check into Statsig experiment variants can be achieved using Feature Gates or Segments. Here are the steps you need to follow:
1. Capture the Initial App Version: The first step is to capture and store the initial app version that a user starts using. This information is crucial as it will be used to determine whether a user is new and started using the app from a specific version onwards.
2. Use Custom Fields for Targeting: The next step is to use Custom Fields for targeting. This will require some code on the client-side that passes in user upgrade/create timestamps as a custom field.
3. Pass the Initial App Version as a Custom Field Key: You need to pass the value for users who started using the app as new users from a specific version as the Custom Field Key.
4. Configure the Custom Field Key: Once you create the key, configure it using the "Greater than or equal to version" operator. This operator checks the current version of the user's app.
For your specific case, you can create two separate experiments or feature gates. One for users on app version 1, where the variants are v1 and v2, and another for users on app version 2, where the variants are v1 to v4. You can then use the app version as a custom field for targeting.
Please note that the Key set in the Custom Field will be included in the events called by Feature Gates. However, it's not a chargeable event. It's just attributes that will be in the payload for events you're already tracking.