Layer 2 (L2)
A layer 2 (L2) is a network built on top of a base blockchain (the layer 1) that processes transactions more cheaply and quickly while relying on the base layer for all or part of its security.
How a layer 2 works
A layer 1 such as Ethereum or Bitcoin is the main chain where final settlement happens. A layer 2 runs its own transaction processing separately, then anchors its results to the layer 1. Users move funds into the L2 through a bridge contract, transact there with lower fees, and can move back to the base chain later.
The key question for any L2 is how much it inherits from the layer 1. Rollups post their transaction data to the base chain and use proofs so that, in principle, anyone can check or challenge the results. Other designs keep data elsewhere and inherit less.
Main types
Optimistic rollups, such as Arbitrum, Optimism and Base, assume batches are valid unless someone submits a fraud proof during a challenge window, often about a week. Zero-knowledge rollups, such as zkSync and Starknet, post a cryptographic validity proof with each batch. On Bitcoin, the Lightning Network uses payment channels instead of rollups.
An example
Say a simple token swap on Ethereum mainnet costs several dollars in gas during a busy hour. The same swap on a rollup might cost a few cents, because thousands of transactions share the cost of one data post to Ethereum. The exact numbers change constantly with demand.
Risks and trade-offs
Many layer 2s still run a single sequencer, the operator that orders transactions. If it goes down, the network can pause, and it could in theory censor users, though most designs offer an escape route through the layer 1. Upgrade keys held by small groups can change contracts quickly.
Bridges are a frequent target for hacks, and withdrawing from an optimistic rollup through the official bridge can take days. Third-party bridges are faster but add their own trust assumptions.
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Frequently asked questions
Are layer 2s as safe as Ethereum?
Not automatically. Their safety depends on proof systems, data availability, upgrade controls and sequencer design, which vary widely between projects.
Why are layer 2 fees lower?
Many transactions are bundled and posted together, so each one pays a small share of the layer 1 cost.
Is Solana a layer 2?
No. Solana is its own layer 1 that scales its base layer directly instead of building on another chain.
Related terms
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