Individually designed 401(k) restatement?

Do individually designed 401(k) plans still need to be restated every 6 years, even though they cannot request a new determination letter?  Or are required amendments sufficient?

Individually designed plans of any kind are no longer on any cycle - previously they were on 5-year cycle. Interim amendments are generally sufficient. Major design changes or a series of substantial amendments would ultimately require restatement, but absent a major law change that probably rarely happens.

I will repeat here my suggestion that as long as the current DL system (Rev. Proc. 2016-37) is in force, never restate. Just keep adding amendments. That way you at least have a base document that has a determination letter, and all for qualification issues are (absent really strange facts) confined to the amendments. For ease of administration, you can do an unsigned "working copy" that cuts and pastes the effective portions of the amendments into the last restatement (that got DL). I think this will save you time with government and private auditors, and also with due diligence reviews in transactions.