It's not a capital gains transaction. It's a receipt of income transaction.
You receive crypto worth $X that you paid $0 for. Thus, you have $X in income and owe income taxes on that. If you paid $Y for the crypto, then you had $X-$Y in income (similar to in-the-money stock options). Your cost basis would be $Y in the $X of coins, so if you ever sell them, then your income is $Z (value at time of sale) less $Y in capital gains.
I'm aware that there's situations where a CGT event occurs even without selling your asset, but this shouldn't be one of them.