Ethereum Layer 2 (Arbitrum, Optimism, Base): taxation

Ethereum Layer 2 (L2) solutions allow transactions to be executed at much lower speed and cost than the main network (L1). Arbitrum, Optimism, Base, zkSync, Scroll and other L2s have their own DeFi ecosystems with their fiscal particularities.

What is a Layer 2?

An L2 is a network that processes transactions outside of Ethereum L1 but inherits its security. The main types are:

• Optimistic Rollups: Arbitrum One, Optimism, Base.
• ZK-Rollups: zkSync Era, Starknet, Polygon zkEVM, Scroll.

Bridges Ethereum ↔ L2: are they taxable events?

When using a bridge to move ETH from Ethereum L1 to Arbitrum:

• You deposit ETH in the L1 bridge contract.
• You receive ETH (wrapped/bridged) in Arbitrum L2.

Tax criterion: If the ownership does not change (you remain the same owner), in principle it is not a transfer. It's like moving money between two accounts of yours.

However: The AEAT has not published specific doctrine on bridges. Some advisors warn that bridging could be interpreted as a transfer if there is a change in the form of the asset. The prudent stance is to log all bridge operations.

The ARB (Arbitrum) airdrop

In March 2023, Arbitrum distributed the ARB token to network users:

• Users who had made transactions on Arbitrum received free ARB.
• Depending on the activity, the airdrop could range from 625 ARB (~€700) to thousands of ARB.

ARB airdrop taxation:

• Equity gain in the general income tax base.
• Valuation: ARB price at the time of the claim (first available market price, ~$1.15/ARB).
• If you made the claim in March 2023 and ARB was worth ~€1.15: that was the profit to be declared in the 2023 income.
• The subsequent sale of ARB generates a second profit/loss based on savings.

OP's airdrop (Optimism)

Optimism also distributed OP tokens in several rounds:

• First round: June 2022.
• Second round: February 2023.
• Same taxation as ARB: capital gain upon receipt, at market price.

Base (from Coinbase): no own airdrop

Base, Coinbase's L2, does not have and does not plan to have a native token. Still:

• Projects built in Base can have their own airdrops.
• The DeFi in Base (Aerodrome, etc.) follows the same tax regime.
• Base operations are cheaper (gas in ETH) but are taxed the same.

DeFi in L2: same rules, lower costs

A swap on Arbitrum (via Camelot or Uniswap on Arbitrum):

• Same tax event as in Ethereum L1.
• The advantage is that gas is much cheaper, making more operations "profitable" net of gas.
• But in terms of NUMBER of operations → there can be many more → more fiscal complexity.

##L2 Native Token Staking

• ARB staking: Arbitrum introduced ARB staking for contributors to the DAO. Rewards → movable capital.
• OP staking: There is no direct OP staking yet (may change).

Gas in L2: still deductible

Gas on Arbitrum is paid in ETH. Each operation consumes ETH in gas:

• Gas paid in ETH = transmission of ETH → possible gain/loss due to difference between price when paying gas and cost of ETH.
• If the gas is very small and the ETH you transmit is also small, the profit/loss can be cents.

Spanish regulations do not provide for a de minimis exemption for small amounts → technically each gas payment should be recorded. In practice, automatic tools (Koinly) calculate it.

ZK-Rollups (zkSync, Starknet): no zkSync airdrop in Spain

zkSync airdropped ZK in June 2024, but blocked it for users from restricted jurisdictions, including the UK. Spain was not explicitly blocked, but some users received it and others did not depending on the characteristics of their wallet.

For those who received it: Capital gain at the market price at the time of receiving ZK.

Summary: Essential registration for L2 users

Updated: April 2026 | Fiscal year: 2025