The IRS Form 1099-K is a tax report that broker-dealers (and some cryptocurrency exchanges such as Coinbase, Gemini, Robinhood, etc.) generate. They keep one copy for themselves, send one copy to you (the user), and one copy to the IRS. This form essentially shows aggregate transaction volume per month.

IRS guidance note has clarified that cryptocurrency is taxed as property, meaning that the capital gains tax is calculated based on the difference between the fair market value at the time a crypto asset is disposed of and the cost basis at which the asset was acquired.