IRS mistakenly (Hypothetical) gave a man one million
Refund. He notified the IRS promptly. It took some time.
To correct it. Question is does he get to keep the bank interest
While he was awaiting instructions

For much smaller amounts, the IRS will not mind you keeping the interest.

For a $1 million, they may ask for it.

Thank you. I just wondered

Glad to help!

I wonder if you’re thinking about the case of the man in FL who filed a tax return claiming $17,000 in wages and $1 million in tax withholding, netting him a (fraudulent) refund check of $980,000?

https://www.nytimes.com/2019/02/16/us/tax-refund-check.html

Similar but different in total