I think the reason NCEES can't release the new code updates yet is to avoid confusion with the April 2021 exam specs. But if we're predicting that the next code cycle will be based on IBC 2018 then you can use IBC's code reference section below to see which codes it will use...
I think because of COVID they delayed the code change for the April 2021 exam. I'm predicting that they will change the codes for October 2021 and use IBC 2018. On a side note, at least for concrete both IBC 2015 and 2018 use ACI 318-14.