Base Bridge: How the Canonical Ethereum–Base Bridge Works

Base is an optimistic-style rollup built on the OP Stack. Its bridge has two directions with very different trust and timing.

Deposits (Ethereum → Base). You send ETH or a supported ERC-20 to the L1StandardBridge or OptimismPortal on Ethereum. The contract locks the funds and emits a message that Base's nodes read, and the same amount is credited on Base ². No challenge period applies, so deposits arrive once Ethereum includes the transaction ¹.

Withdrawals (Base → Ethereum). Funds are burned or locked on Base. Ethereum then has to accept a proof that Base's state includes your withdrawal. Since the Azul upgrade (May 2026), two proof types exist ⁵:

• a TEE proof, made in trusted hardware by a permissioned prover;
• a ZK proof, which anyone can submit and which overrides a conflicting TEE proof.

When both agree, the withdrawal can finalize after 1 day. Otherwise a single-proof dispute game runs for 5 days. That window was cut from 7 days in the Beryl upgrade on June 25, 2026 ³⁴. After the window ends, you send a final transaction on Ethereum to claim the funds.

The bridge.base.org page is gone. Base's docs list these routes as of October 23, 2026 ¹:

Base's docs warn that "fast bridges do not inherit Base's security" and that Superbridge can also route through third-party bridges ¹. Check which route is selected before you sign.

A typical canonical deposit from Ethereum:

1. Connect a wallet to Superbridge or Brid.gg and pick Ethereum → Base.
2. Choose the asset and amount, approve the token if it is an ERC-20, and confirm.
3. Pay Ethereum gas; the funds appear on Base after the deposit is processed.

For withdrawals, expect at least two Ethereum transactions (prove and finalize) and a 1–5-day wait in between.

The canonical bridge charges no bridge fee of its own. You pay:

• Ethereum gas for deposits, and for the prove and finalize steps of a withdrawal. This is usually the largest cost.
• Base gas for the withdrawal's initiating transaction (normally small).
• Front-end or route fees if a third-party interface or fast bridge adds them.

Fast bridges trade a fee or spread for speed: you receive funds from their liquidity in seconds or minutes, and they wait out the canonical window themselves ¹³.

The contracts are upgradeable. Base's docs list a ProxyAdmin owner, a Guardian, an Incident Multisig, a Coinbase multisig and a Base Security Council multisig ². Coinbase Technologies manages the keys that post Base's transaction batches, propose state outputs and act as challenger ². Azul's permissionless ZK override was presented as a step toward less reliance on these operators ⁵. Users still depend on the multisigs not to push a harmful upgrade.

Base also runs a separate bridge to Solana for SOL and SPL tokens, with cross-chain messaging and optional automatic relaying. Its Base contract is 0x3eff766C76a1be2Ce1aCF2B69c78bCae257D5188, and its Solana program is HNCne2FkVaNghhjKXapxJzPaBvAKDG1Ge3gqhZyfVWLM ¹. It uses different contracts from the Ethereum bridge and should be assessed separately.

• Withdrawal wait. Funds sent to Ethereum through the canonical route are locked for 1–5 days ¹³.
• Upgrade keys. Multisigs can change the bridge contracts ².
• Sequencer outages. When Base stops producing blocks, deposits and withdrawals stall too (see below) ⁷⁸.
• Wrong route. Fast bridges and aggregators carry their own contract and liquidity risk ¹.
• Fake tokens. Verify ERC-20 addresses against the Superchain token list; Base's docs recommend testing with a small amount first ¹.
• Phishing. The old bridge.base.org domain no longer hosts the bridge. Treat any "Base bridge" site asking for a seed phrase as a scam.