The best thing about the taxes is you only pay when you cash out from what I can see you dont have to claim gains unless you cash out vs stocks you have to tally up your gains and losses on the sells for the year which I think is dumb if your not cashing out.
I’d triple check with lawyers and accountants on this, as have heard both things and not sure where the matter stands with the most recent tax law updates...
from what I can tell if you trade on bittrex binance or other non linked with bank account exchanges then you are fine its only when you send funds into an account (cash out) that the bank recieving will report to IRS. So even coinbase I believe is not the one reporting to the IRS its the individual customers banks receiving the deposits from coinbase when you withdrawl. So as far as I can tell No agency can know your gains for trading because many of the exchanges are not connected to banks
Though if you were to keep such activity hidden and eventually get busted, it might be considered tax fraud.