Regardless of which type of token the holder receives, the IRS treats these tokens the same. The IRS recognizes that a taxable event occurs when you exchange one cryptocurrency for another. In an ICO/IEO, you may receive the tokens in the future. Then you will not recognize gain until you receive the token. However, the cost basis is derived from when the sale or exchange of the cryptocurrency occurred, and as such, your cost basis will relate back to the date where you originally participated in the ICO/IEO.