The IRS ?nor sure about that, anyway it obviously is not going out in one ‘blast’ so possible they ‘blasting’ a few banks at a time
They might be batching out by bank for the smaller banks. But a large percentage of recipients bank with the top 5-10 largest banks in the US. I doubt Wells Fargo, Chase, Citi, BofA, US bank etc are each going to just get one file with all the ACH deposits.