Only available on WooCommerce License Keys extended plugin.
As part of the extended features, WooCommerce License Keys will support any variable product type that uses the standard WooCommerce variation form.
Editing Variable Products
A License Key checkbox will appear when editing a variation, when this option is checked, a license key form will appear with all the license key inputs supported for the variation.
The options available are the same as for the license key product (this includes all the extended features). Although they may be some variations depending on if you are using 3rd party subscriptions.
The API will work well with the variation too, just remember to specify the SKU.
Product Page
The variable product will behave as usual, the only difference is that a license details table will appear below the variation price every time a variation is selected. The table information will change depending on the variation selected.