Airdrop eligibility: snapshots, sybil filters and why wallets get excluded

Airdrop eligibility is whatever the project decides it is. It records wallet activity at a fixed snapshot, scores wallets against criteria that are often published only when the airdrop is announced, and then removes wallets it believes are bots or one person farming with many addresses, wallets in blocked countries, and anything else its terms exclude. Activity after the snapshot does not count for that round, and the project's terms usually give it the final word.

Step 1: the snapshot

A snapshot fixes the moment that counts. Uniswap's UNI airdrop, announced on 16 September 2020, used "a snapshot ending September 1, 2020, at 12:00 am UTC". It gave 400 UNI to each of 251,534 addresses that had "ever called the Uniswap v1 or v2 contracts", including about 12,000 addresses that had only ever submitted failed transactions, and split a separate pool between 49,192 past liquidity providers in proportion to their liquidity.

Later airdrops follow the same shape, with a gap between the snapshot and the claim:

• Arbitrum (ARB): snapshot at block 58642080 on Arbitrum One, 6 February 2023; claims opened on 23 March 2023 (Arbitrum Foundation).
• Optimism (OP), Airdrop 1: "A snapshot of addresses was taken on 03-25-2022 0:00 UTC", and claims opened in May 2022 (Optimism).
• ZKsync (ZK): snapshot on 24 March 2024 at 00:00 UTC; user claims opened in the week of 17 June 2024 (ZK Nation).

In each case the snapshot was in the past by the time anyone could claim: 15 days for Uniswap, about six weeks for Arbitrum, close to three months for ZKsync. Uniswap's is the classic retroactive airdrop: it rewarded what wallets had done before the rules were published.

Step 2: the criteria

Each project scores what it wants to reward, and the lists differ widely.

• Arbitrum used points: at most one per qualifying action before the snapshot, such as bridging funds into Arbitrum One, transacting in 2, 6 or 9 different months, making more than 4, 10, 25 or 100 transactions (or interacting with as many contracts), or transacting more than $10,000, $50,000 or $250,000 in aggregate value. Scores were capped at 15, and "Less than 3" points meant "Not eligible".
• Optimism had six criteria sets: OP Mainnet users, repeat OP Mainnet users, DAO voters, multisig signers, Gitcoin donors and "users priced out of Ethereum". 248,699 addresses qualified, and an address could match several sets and receive the sum.
• ZKsync required at least one of seven criteria, such as interacting with "at least 10 non-token smart contracts" or trading "at least 10 distinct ERC-20 tokens", then scaled each allocation by how much was sent to ZKsync Era and how long it stayed there. 695,232 wallets were eligible.

Criteria like these are each project's own choice, so a list of tasks that "guarantee" an airdrop, from anyone but the project, is a guess. A points program publishes a score as you go, but even there the final formula is the project's; see airdrop points programs.

Step 3: sybil filters

A sybil attack on an airdrop is one person posing as many. The Arbitrum Foundation defines sybil accounts as accounts "controlled by an entity trying to create the false appearance of being many entities via deceptive on-chain activity in order to unfairly game" the airdrop. The filters that projects have published look for the patterns such farms leave behind.

• Arbitrum subtracted a point if all of a wallet's transactions fell within a 48-hour period, subtracted another if it held less than 0.005 ETH and had interacted with no more than one smart contract, and disqualified addresses identified as sybils in the Hop protocol's bounty program. It also built a graph of all Arbitrum One transactions and collapsed each likely sybil cluster "into a single recipient account".
• ZKsync grouped wallets that sent funds to the same exchange deposit address, or that were funded by the same source with similar amounts inside a time window, and filtered out every cluster of more than 20 wallets. One swarm it published had 1,029.
• Optimism applied more filtering after announcing Airdrop 1, which "excludes 17k addresses and recovers 14m OP", redistributed the recovered OP to the remaining addresses, and said it would not publish those additional filters.
• LayerZero, on 3 May 2024, gave sybil farmers 14 days to self-report "in return for 15% of their intended allocation", said those it identified who did not "will receive nothing", and listed behaviour it counted as sybil, including bridging "$0.01 back and forth across chains for the sake of having touched a chain."
• Hamster Kombat, the Telegram game, said on 22 September 2024 that 131 million players qualified and "around 2.3 million were banned as cheaters", as quoted by Decrypt (news report).

Filters are heuristics, and the projects say so. ZKsync says its sybil detection "intentionally used a very conservative heuristics framework, to avoid accidentally punishing real people", and Optimism wrote that "It's impossible to catch everything". Under a funding heuristic like ZKsync's, a real person who funded many wallets from one source would look like a cluster.

Other reasons a wallet is excluded

• Where you live. ZKsync blocked Cuba, Iran, North Korea, Russia, Syria and the Crimea, Donetsk and Luhansk regions of Ukraine, citing sanctions rules from the US Treasury's OFAC, the UN Security Council, the EU's External Action Service and HM Treasury, and added that "persons residing in the United States will also be prohibited". The Eigen Foundation's airdrop terms (last revised 9 May 2024) describe geo-location screening and "proxy and VPN detection and blocking controls", and say that circumventing its geo-blocking "may permanently disqualify you".
• Exchange addresses. Optimism filtered out "known centralized exchange and fiat on-ramp addresses".
• Too little activity. Arbitrum's 3-point minimum, ZKsync's one-point minimum, and Optimism's rule that an address had to have used Ethereum for more than 1 day (24 hours between its first and last transaction) for its Ethereum criteria.
• The project's discretion. The Eigen terms say the Foundation "shall have no obligation to notify actual or potential Airdrop participants of the eligibility criteria for any Airdrop prior to, during, or after the claims are opened", and may disqualify a participant who "may have used multiple addresses to obscure its identity or location or to attempt to game, cheat, or hack the Airdrop".
• A missed claim period. ARB claiming ended on 24 September 2023, and the Arbitrum Foundation's page now says "$ARB is no longer claimable." Projects handle leftovers differently: on 15 September 2023 Optimism sent unclaimed Airdrop 1 OP straight to the eligible addresses.

Checking eligibility without getting scammed

Projects warn about fake sites themselves. The Arbitrum Foundation put its warning at the top of its specification: "The only official website for the $ARB airdrop is https://arbitrum.foundation. There is no presale. Don't ever share your seed phrase."

1. Reach the checker from the project's own website or docs, never from a direct message, an ad or a reply under a post.
2. Read what your wallet asks you to sign. LayerZero's self-report, for example, asked users to "Sign message to prove ownership of address". A request for a token approval is a different thing: it gives a contract permission to move your tokens.
3. Never enter a seed phrase anywhere to check or claim an airdrop. A legitimate airdrop never asks for a seed phrase or private key.
4. Treat offers to "fix" your eligibility as scams. Under the Eigen terms, eligibility "is subject to our sole discretion", meaning the Foundation's, so no third party can grant it.

How to claim a crypto airdrop safely and airdrop scams cover the rest, and Hamster Kombat is one listing on this site where a ban wave decided who could claim.

Key takeaways

• Eligibility is set by the project: a snapshot, then criteria, then filters, often published only when the airdrop is announced.
• Activity after the snapshot does not count for that round.
• Sybil filters look for clusters: shared funding, shared exchange deposit addresses, bursts of activity and tiny balances.
• Wallets are also excluded for their location, VPN use, exchange addresses, too little activity or a missed claim window.
• An official eligibility check never needs your seed phrase.