When new expiration months appear?

When does a expiration appear? For example, when will April 2021 appear SPX options? Is there a schedule?

 

I think, at the current stop, plans may change.

 

What does it mean? Current stop?

 

http://www.cboe.com/products/stock-...ons-with-a-m-settlement-spx/spx-options-specs
===============
Expiration Months:
Up to twelve (12) near-term months. In addition, the Exchange may list up to ten (10) SPX LEAPS® expiration months that expire from 12 to 60 months from the date of issuance.
===============
(didn't see more detailed info but you can actually contact CBOE, they're often responsive)

 

I wanted to say that now is a time when it is quite difficult to plan, because everything can change a lot.