[patio11]

The IRS does not in the ordinary course receive informational returns about people's bank accounts. They do receive informational returns about interest generated by bank accounts (and other places), but they don't get e.g. transaction lists by default. Google "1099-INT example" to see one of these informational returns. They're minimalistic and they are minimalistic precisely because a large portion of the US polity hates the notion that the IRS would have arbitrary read access to people's financial lives.

You can reasonably assume that the IRS can use subpoena power to compel a US financial institution or foreign financial institution to surrender records to it. This is an oppositional process and they use it relatively rarely next to the total universe of taxpayers and accounts, generally only after they already have evidence of hinkiness and want to quantify unsurveilled amounts and/or locate assets.

These are not secret facts about the world; the operations of the IRS are exhaustively public (trust me, I have weird hobbies). People on a programmer-dense message board should have more weight for "While I understand that X would be accomplishable via an API if it existed, it is possible that that API does not factually exist" than they often do.

Also, the number of times someone in the financial industry typed in git commit -m "tldr Patriot Act compliance" is orders of magnitude below the number that HN comments routinely predict.