The guys from CKSource just launched the first version of CKEditor 5.
Is it safe to use it on a production environment? ( update the platform using it from 4.x to 5 ) or better to wait for the next minor versions?
When reading this answer please do mind that it might've got outdated with time.
First of all, check out the Browser Compatibility guide. It's a source of up to date information about the stability of CKEditor 5 on various browsers and environments.
Second of all, CKEditor 5 is a new product, designed and built from scratch. When migrating from CKEditor 4 to it you may find some features missing. You'll need to check that yourself. You can also check the Migration from CKEditor 4 to CKEditor 5 guide.
Finally, we do generally recommend testing CKEditor 5 yourself. There's no point to upgrade CKEditor 4 to CKEditor 5 if you'd miss something in it.
tl;dr: CKEditor 5 is production ready for specific use cases. To know if it's ready for you, test it :)