If I say in my diary "I give $100,000 to dublinben", or "dublinben can claim $100,000 from me for free by just asking", nothing has happened yet from the perspective of the IRS.
Nobody has any obligation to claim their coins, and even if they do, it will be private and nobody will know.
This is unlike Bitcoin forks or ERC-20 airdrops, because it’s 100pct opt-in.
The rule is you need to pay taxes on the value when you receive them, and then the profit / loss when you convert them to fiat, or another currency. Both are taxable events.