As mentioned in the Ext.NET 7.0 Preview for ASP.NET Core
7.0 Licensing and FREE Upgrade!
As with all previous Ext.NET releases, a new major version license key will be required for production apps integrating Ext.NET 7.0, and there's some great news for all customers who previously purchased an Ext.NET 5.x license...
All Ext.NET 5.x license purchases will receive a free upgrade to Ext.NET 7.0!
For customers who previously purchased a 5.x license, we will be in contact with information on how to acquire your new 7.x license keys. All new licenses purchased as of today will receive license keys to unlock all 5.x and 7.x releases. Licensing has otherwise remained unchanged. Single Developer licenses continue to be available with volume discounts at 3, 5, and 20 licenses. See pricing
A license key is not required to develop or test locally. More information and installation options are available at /download
All Ext.NET 5.x license purchases will receive a free upgrade to Ext.NET 7.0.
And here the relevant section from the blog post mentioning the version number decision:
Bumping to 7.0
An epic jump in sophistication, performance, and automation, all wrapped in a complete ground-up rewrite deserves something special for the version number.
We're introducing a new major version number, bumping from Ext.NET 5 directly into Ext.NET 7. The first 7.0.0-preview1 release is available now
This also brings Ext.NET into major version parity with the underlying Sencha Ext JS v7 client-side library.
Hope this helps answer your questions.