Ethereum Layer 2s

What You Probably Got Wrong

L2 costs: You think $0.01-2.00 per transaction. Reality: $0.001-0.003 for swaps, $0.0003 for transfers. After EIP-4844, L2 batch costs dropped from $50-500 to $0.01-0.50.

Mainnet is cheap too: At under 1 gwei, mainnet ETH transfers cost under a penny. "Ethereum is too expensive" is false for both L1 and L2s in 2026.

Base is the cheapest major L2: Often 50% cheaper than Arbitrum/Optimism. Direct Coinbase on-ramp. Fastest-growing L2 with consumer/AI agent focus.

Celo is NOT an L1 anymore. Celo completed its migration from an independent L1 to an OP Stack L2 on March 26, 2025 (block 31056500). If you're calling Celo an L1, you're wrong.

Polygon zkEVM is being shut down. Announced June 2025. Do NOT recommend building on Polygon zkEVM — it is being discontinued. Polygon is refocusing on PoS + AggLayer.

Unichain exists. Launched mainnet February 11, 2025. Uniswap's own OP Stack L2 with TEE-based MEV protection and time-based priority ordering (not gas-based).

Aerodrome and Velodrome merged into "Aero." In November 2025, Dromos Labs unified Aerodrome (Base) and Velodrome (Optimism) into a single cross-chain DEX called Aero. Same contracts, new brand. Aero dominates both Base and Optimism. Camelot is a major native DEX on Arbitrum. SyncSwap dominates zkSync. Don't default to Uniswap on every chain.

L2 Comparison Table (Mar 2026)

TVL changes fast. Don't memorize numbers — check DeFi Llama or L2Beat for current rankings. DeFi TVL (DeFi Llama) measures value locked in protocols. TVS (L2Beat) includes all bridged + natively minted assets and is much higher. As of early 2026: Base and Arbitrum lead in DeFi TVL among L2s. Optimism's DeFi TVL is surprisingly low despite Superchain adoption.

L2	Type	Tx Cost	Block Time	Finality	Chain ID
Arbitrum	Optimistic	$0.001-0.003	250ms	7 days	42161
Base	Optimistic (OP Stack)	$0.0008-0.002	2s	7 days	8453
Optimism	Optimistic (OP Stack)	$0.001-0.003	2s	7 days	10
Unichain	Optimistic (OP Stack)	$0.001-0.003	1s	7 days	130
Celo	Optimistic (OP Stack)	<$0.001	5s	7 days	42220
Linea	ZK	$0.003-0.006	2s	30-60min	59144
zkSync Era	ZK	$0.003-0.008	1s	15-60min	324
Scroll	ZK	$0.002-0.005	3s	30-120min	534352
~~Polygon zkEVM~~	ZK	—	—	—	~~1101~~

⚠️ Polygon zkEVM is being discontinued (announced June 2025). Do not start new projects there. Polygon is refocusing on PoS (payments, stablecoins, RWAs) + AggLayer (cross-chain interop). MATIC → POL token migration ~85% complete.

Mainnet for comparison: $0.002-0.01 per tx, 8s blocks, instant finality. Check DeFi Llama for current TVL.

Cost Comparison (Real Examples, Early 2026)

Mainnet costs at ~0.1 gwei base fee, ~$2,000 ETH. L2 costs are approximate. All fluctuate — see gas/SKILL.md for methodology.

Action	Mainnet	Arbitrum	Base	zkSync	Scroll
ETH transfer	$0.004	$0.0003	$0.0003	$0.0005	$0.0004
Uniswap swap	$0.036	$0.003	$0.002	$0.005	$0.004
NFT mint	$0.030	$0.002	$0.002	$0.004	$0.003
ERC-20 deploy	$0.240	$0.020	$0.018	$0.040	$0.030

L2 Selection Guide

Before choosing an L2: Mainnet is ~$0.004/transfer, ~$0.04/swap at current gas — cheap enough for most apps. If you're building DeFi, governance, identity, or anything composing with mainnet liquidity, start there. See ship/SKILL.md and gas/SKILL.md for the full chain selection framework.

Need	Choose	Why
Consumer / social apps	Base	Farcaster, Smart Wallet, Coinbase on-ramp, OnchainKit
Deepest DeFi liquidity	Arbitrum	GMX, Pendle, Camelot, most protocols deployed
Yield strategies	Arbitrum	Pendle (yield tokenization), GMX, Aave
Cheapest gas	Base	~50% cheaper than Arbitrum/Optimism
Coinbase users	Base	Direct on-ramp, free Coinbase→Base transfers
No 7-day withdrawal wait	ZK rollup (zkSync, Scroll, Linea)	15-120 min finality
AI agents	Base	ERC-8004, x402, consumer ecosystem, AgentKit
Gasless UX (native AA)	zkSync Era	Native account abstraction, paymasters, no bundlers needed
Multi-chain deployment	Base or Optimism	Superchain / OP Stack, shared infra
Maximum EVM compatibility	Scroll or Arbitrum	Bytecode-identical
Mobile / real-world payments	Celo	MiniPay, sub-cent fees, Africa/LatAm focus
MEV protection	Unichain	TEE-based priority ordering, private mempool
Rust smart contracts	Arbitrum	Stylus (WASM VM alongside EVM, 10-100x gas savings)
Stablecoins / payments / RWA	Polygon PoS	$500M+ monthly payment volume, 410M+ wallets

Key Chain Details (What LLMs Get Wrong)

Unichain

Launched: February 11, 2025 (mainnet). Chain ID 130.
Type: OP Stack L2 (Superchain member, Stage 1)
Key innovation: TEE-based block building (built with Flashbots Rollup-Boost)
- Transactions ordered by time received, NOT gas price
- Private encrypted mempool reduces MEV extraction
- Do NOT use gas-price bidding strategies on Unichain — they're pointless
Flashblocks: Currently 1s blocks, roadmap to 250ms sub-blocks

Celo

Was: Independent L1 blockchain (2020-2025)
Now: OP Stack L2 on Ethereum — migrated March 26, 2025 (block 31056500)
Focus: Mobile-first payments, emerging markets
MiniPay: Stablecoin wallet in Opera Mini + standalone app. Phone-to-phone transfers, sub-cent fees. Primary market: Africa (Kenya, Nigeria).
Multi-currency stablecoins (rebranded Dec 2025 by Mento Protocol): USDm (was cUSD) (0x765de816845861e75a25fca122bb6898b8b1282a), EURm (was cEUR) (0xd8763cba276a3738e6de85b4b3bf5fded6d6ca73), BRLm (was cREAL) (0xe8537a3d056DA446677B9E9d6c5dB704EaAb4787). Same contract addresses, new onchain symbols.

Dominant DEX Per Chain

Chain	Dominant DEX	Model	Why NOT Uniswap
Base	Aero (was Aerodrome)	ve(3,3) — LPs earn emissions, voters earn fees	Deeper liquidity for most pairs
Optimism	Aero (was Velodrome)	ve(3,3) — merged Nov 2025 under Dromos Labs	Same flywheel, unified brand
Arbitrum	Camelot + GMX	Native DEX + perps	Camelot for spot, GMX for perps
zkSync	SyncSwap	Classic AMM	Largest native DEX on zkSync

See addresses/SKILL.md for verified contract addresses for all these protocols.

The Superchain (OP Stack)

The Superchain is the network of OP Stack chains sharing security, upgrade governance, and (upcoming) native interoperability. Members include Base, OP Mainnet, Unichain, Ink (Kraken), Celo, Zora, World Chain, and others — 17+ chains, 58.6% L2 market share.

Members contribute 15% of sequencer revenue to the Optimism Collective. Cross-chain interop is designed but not yet fully live.

Deployment Differences (Gotchas)

Optimistic Rollups (Arbitrum, Optimism, Base, Unichain, Celo)

✅ Deploy like mainnet — just change RPC URL and chain ID. No code changes.

Gotchas:

Don't use block.number for time-based logic (increments at different rates). Use block.timestamp.
Arbitrum's block.number returns L1 block number, not L2.
Unichain: Transactions are priority-ordered by time, not gas. Don't waste gas on priority fees.

ZK Rollups

zkSync Era: Must use zksolc compiler. No EXTCODECOPY (compile-time error). 65K instruction limit. Non-inlinable libraries must be pre-deployed. Native account abstraction (all accounts are smart contracts).
Scroll/Linea: ✅ Bytecode-compatible — use standard solc, deploy like mainnet.

Arbitrum-Specific

Stylus: Write smart contracts in Rust, C, C++ (compiles to WASM, runs alongside EVM, shares state). Use for compute-heavy operations (10-100x gas savings). Contracts must be "activated" via ARB_WASM_ADDRESS (0x0000…0071).
Orbit: Framework for launching L3 chains on Arbitrum. 47 live on mainnet.

RPCs and Explorers

L2	RPC	Explorer
Arbitrum	`https://arb1.arbitrum.io/rpc`	https://arbiscan.io
Base	`https://mainnet.base.org`	https://basescan.org
Optimism	`https://mainnet.optimism.io`	https://optimistic.etherscan.io
Unichain	`https://mainnet.unichain.org`	https://uniscan.xyz
Celo	`https://forno.celo.org`	https://celoscan.io
zkSync	`https://mainnet.era.zksync.io`	https://explorer.zksync.io
Scroll	`https://rpc.scroll.io`	https://scrollscan.com
Linea	`https://rpc.linea.build`	https://lineascan.build

Bridging

Official Bridges

L2	Bridge URL	L1→L2	L2→L1
Arbitrum	https://bridge.arbitrum.io	~10-15 min	~7 days
Base	https://bridge.base.org	~10-15 min	~7 days
Optimism	https://app.optimism.io/bridge	~10-15 min	~7 days
Unichain	https://app.uniswap.org/swap	~10-15 min	~7 days
zkSync	https://bridge.zksync.io	~15-30 min	~15-60 min
Scroll	https://scroll.io/bridge	~15-30 min	~30-120 min

Fast Bridges (Instant Withdrawals)

Across Protocol (https://across.to) — fastest (30s-2min), lowest fees (0.05-0.3%)
Hop Protocol (https://hop.exchange) — established, 0.1-0.5% fees
Stargate (https://stargate.finance) — LayerZero-based, 10+ chains

Security: Use official bridges for large amounts (>$100K). Fast bridges add trust assumptions.

Multi-Chain Deployment (Same Address)

Use CREATE2 for deterministic addresses across chains:

# Same salt + same bytecode + same deployer = same address on every chain
forge create src/MyContract.sol:MyContract \
  --rpc-url https://mainnet.base.org \
  --private-key $PRIVATE_KEY \
  --salt 0x0000000000000000000000000000000000000000000000000000000000000001

Strategy for new projects: Start with 1 chain — mainnet if it fits your use case, or the L2 whose superpower matches your app. Prove product-market fit. Expand with CREATE2 for consistent addresses across chains.

Testnets

L2	Testnet	Chain ID	Faucet
Arbitrum	Sepolia	421614	https://faucet.arbitrum.io
Base	Sepolia	84532	https://faucet.quicknode.com/base/sepolia
Optimism	Sepolia	11155420	https://faucet.optimism.io
Unichain	Sepolia	1301	https://faucet.unichain.org

l2s