In one sentence
Like Base, Arbitrum is an Optimistic Rollup that executes transactions off Ethereum and hands the books back to it (the basics of Layer 2s are at the start of the Base guide). The differences: Offchain Labs built the technology itself from scratch, it launched earlier, and it has its own governance token, ARB, and a DAO.
Where it came from
Offchain Labs was founded by Princeton computer scientist Ed Felten and his students.
- August 2021: Arbitrum One opened to the public, one of the first Ethereum Layer 2s usable at scale. Ethereum fees were extremely high then, many DeFi protocols moved over, and perpetuals protocols such as GMX grew up here.
- August 2022: the Nitro upgrade replaced the core with a modified Ethereum client, sharply improving fees and speed.
- March 2023: the ARB token was issued and airdropped to early users, and the Arbitrum DAO was formed.
- 2025: a new dispute protocol, BoLD, went live, letting anyone take part in validating and challenging wrong results, not just a list of approved firms.
Offchain Labs also offers Orbit, which lets other projects build their own chains on the same technology (see Custom chains), and Stylus, which lets developers write contracts in Rust and other languages.
Who produces blocks, and who checks
As on Base, Arbitrum currently has one sequencer, run by an Offchain Labs-related entity. Measured, it produces a block every 277 ms, making it one of the fastest Ethereum Layer 2s.
Correctness is guaranteed by fraud proofs: once someone records an execution result on Ethereum, anyone who thinks it is wrong can challenge it. The two sides narrow down their disagreement step by step on Ethereum until it comes down to one specific instruction, and Ethereum rules who is right. The loser forfeits their bond. This “interactive” proof saves on-chain resources, but a single challenge may take several rounds.
- 01Signed and sent
The transaction goes to the sequencer. Fees are paid in ETH.
Instant - 02Sequencer produces a block
The sequencer orders transactions as received and produces a Layer 2 block.
About 277 ms per block - 03Batched to Ethereum
Transaction data is compressed and submitted to Ethereum mainnet.
Within minutes - 04Result recorded
A validator records the execution result on Ethereum and posts a bond.
- 05Challenge period ends
The result is final only if no challenge succeeds within about 6.4 days. Official bridge withdrawals wait this long.
About 6.4 days
What ARB and the DAO control
ARB is not used to pay fees (fees are still in ETH). It is a governance token: holders vote on Arbitrum DAO proposals, including protocol upgrades, spending from the DAO treasury and funding ecosystem projects.
Day-to-day emergency actions and some upgrade powers sit with a “Security Council”, whose members are elected by the DAO and need a majority of signatures to act. This is one reason L2BEAT does not yet rate it Stage 2: in an emergency the council can upgrade contracts without a waiting period. ARB’s market cap is $1.33B.
- Stage 0
Still on "training wheels": proofs may not be live, or the operator can change the rules alone
- Stage 1
Proofs are live, but a security council can still override or upgrade in an emergency
- Stage 2
Fully governed by code and proofs; nobody can change outcomes unilaterally
What is on-chain today
- USDT 22% $797M
- USDC 65% $2.31B
- Other 13% $461.1M
Sources: CoinGecko (market cap, supply), DefiLlama (TVL, stablecoins, DEX volume, fees, protocols), measurements from public nodes (block time, validators).
Things worth noticing:
- A long-standing DeFi home: lending and perpetuals protocols such as Aave, GMX and Fluid lead by locked value.
- “Hyperliquid Bridge” ranks near the top: the official route for depositing USDC to Hyperliquid is deployed on Arbitrum, so a lot of USDC sits here waiting to be deposited or withdrawn.
- Stablecoins total $3.57B, more than all locked value, which suggests a lot of stablecoins just sit on the chain for transfers and trading rather than in DeFi protocols.
Strengths and trade-offs
- Fast blocks, low fees, a long track record and many large DeFi protocols.
- Challenging wrong results is open to everyone (BoLD); L2BEAT rates it Stage 1.
- A DAO and a token let the community vote on upgrades and spending.
- One sequencer, so censorship and downtime are possible (you can force inclusion via mainnet, but it may take up to about a day).
- The Security Council can upgrade contracts immediately in an emergency, leaving users no window to exit.
- ARB cannot pay fees; its value comes mainly from governance rights, and ongoing unlocks weigh on the price.
- 01
Was the project token issued natively on Arbitrum or bridged from Ethereum? Check how the contract was created and the bridge records on Arbiscan.
- 02
Is the contract upgradeable, and who holds the upgrade key (a single signer, a multisig, or governance with a timelock)?
- 03
For perpetuals projects, check the oracle source and liquidation mechanism; Arbitrum has many such projects, and many incidents.
- 04
For anything involving Hyperliquid deposits and withdrawals, confirm you are using the official bridge contract address.
Data and sources
- Live figures: CoinGecko (ARB market cap), DefiLlama (locked value, stablecoins, DEX, fees), L2BEAT (security stage and risks) and a public Arbitrum node (measured block time).
- Mechanisms are based on the official Arbitrum documentation and L2BEAT’s project page.
- This guide is educational and is not investment advice.
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