Do you migrate OLD sites to DIVI 5

As a freelancer, I’m managing a lot of client sites—plus several of my own—all built on Divi 4. The last six or so new builds have been in Divi 5, and I’m comfortable working with it for fresh projects.

What I’m trying to figure out is this: Will I eventually need to migrate all my older sites to Divi 5, or will Divi 4 continue running reliably as-is?

With the number of legacy sites I have, upgrading everything to 5 would be a massive, time‑consuming headache, so I’m hoping it’s not mandatory.