Benefits of upgrading to V4 can be found in this FAQ article

If you have websites created with website builder V3, the following migration options are available for your customers' websites:

• (Recommended) We automatically migrate all your websites to website builder V4 (if there will be any concerns from your customers, please create a ticket and we will fix all issues);
• We manually migrate all your websites, check quality of migration and make slight changes (if needed) for an additional fee.

Note: Since December 2021, Website builder V3 is EOL (end-of-life) and is no longer supported.

In early 2023, we began automatically migrating all V3 websites to V4 for Cloud brands .