A perpetual fallback license is a license that allows you to use a specific version of software without an active subscription for it. The license also includes all bugfix updates, more specifically in X.Y.Z version all Z releases are included.
When purchasing an annual subscription, you will immediately get a perpetual fallback license for the exact version available at the time.
If paying on a monthly basis, as soon as you pay for 12 consecutive months, you will receive this perpetual fallback license providing you with access to the exact product version for when your 12 consecutive months subscription started. You will receive perpetual fallback licenses for every version you’ve paid 12 consecutive months for.
This option is available whether you subscribe to a single product or the ‘All Products’ option.
See some examples in charts below:
If you are an Administrator, the version each subscription will continue working with after it expires is shown in the "Fallback Product" column.
If you are a subscription license User, the version you can continue using after the subscription expires is shown at the main login page at https://account.jetbrains.com/login