HIFO tax method clarification

When it comes to crypto taxes, I’m using HIFO for figuring out my cost basis. I know FIFO would’ve been much easier, but here we are. I’m kinda confused about what "cost basis" really means under the IRS rules for cryptocurrency in the US. Does it refer to the price of 1 unit (like 1 BTC) at the time I bought it, no matter how many I got? Or is it the total price I paid for what I bought? So, here’s what’s in my wallet: Lot A: 0.2 BTC that I bought for $6,000 when BTC was at $30,000. Lot B: 0.5 BTC that I bought for $10,000 when BTC was at $20,000. According to the HIFO rule, if I spend 0.1 BTC from my wallet, which lot does that come from, A or B?

Did you try to ask Chat GPT or any other LLM for that matter beforehand?