First - this will apply to HN users with a Keybase account who have opted in to the airdrop, not all HN users.

I am not a CPA, but I think there are two things involved here (for people in the US):

1. This is a gift, but the value of it (about $20 right now) is less than the gift tax threshold. 2. Lumens are probably (?) treated like bitcoin, which are treated like a security, not currency.

I think this means that yes, there are tax implications. You will be obligated to pay short- or long-term capital gains tax when you elect to 'sell' the Lumens, and the cost basis will be the fair market value of the Lumens on the day you receive them from SDF.

Again, not a CPA, tax lawyer, or anything like that.

It depends on how you interpret your jurisdiction's tax laws. in the united states there are some tax professionals that would count airdrops as taxable, and others that wouldn't if you never plan to claim the airdrop.