MTD for VAT below threshold - when is start date?

My original recollection is that back in 2017 the then chancellor gave 'below vat threshold' traders an extra year.  So the mandatory start date of  first period after 1/4/19 was introduced for all registered traders with taxable turnover greater than £85k.

Looking at the current guidance, all I can find for 'below' traders is a suggestion that they are allowed/encouraged to join on a voluntary basis.

Can someone enlighten me - are 'below' traders no longer mandated into MTD next April?

Thanks in advance

Nidge