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Lending rewards are received in exchange for loaning out a cryptoasset.
There is no IRS guidance on lending rewards, so you would need to examine the details of the transactions you are undertaking to determine the tax treatment.
Following the IRS' tax treatment of staking, it seems clear that lending rewards will be subject to income tax. The USD value of the rewards (usually crypto tokens) at the date of receipt will be the value of the taxable miscellaneous income.
The USD value of the reward at the date of receipt is the capital gains tax acquisition cost of the tokens; to be deducted from the proceeds of a later disposal of the tokens (which is subject to capital gains tax).