Arbitrum, Arbitrum One, Nova and ARB: what is what
People use the names Arbitrum and Arbitrum One as if they meant the same thing. Most of the time the difference does not matter. When you send money, it does. This page sorts out the names: the technology, the networks and the token.
Arbitrum is a technology for scaling Ethereum, and the name of the family of networks built with it. Arbitrum One is the first public network of that family: a layer 2 on Ethereum, with the chain ID 42161 and fees paid in ETH. An app that says it runs on Arbitrum usually means Arbitrum One. Arbitrum Nova is a separate network, and ARB is a governance token, not the coin that pays the fees.
Is Arbitrum the same as Arbitrum One?
Not quite. The word Arbitrum names three things: a technology for building networks on top of Ethereum, the family of networks built with it, and the community that governs two of them. The name Arbitrum One belongs to a single network, the first public one of the family.
In everyday use the two names are swapped freely. An app that says it runs on Arbitrum usually runs on Arbitrum One. Wallets usually list the network as Arbitrum One; exchanges list it under either name.
Arbitrum One opened to the public on 31 August 2021. Offchain Labs, the company that developed the technology, built the network and still runs part of it. Since March 2023 the Arbitrum DAO governs it.
How Arbitrum One works on top of Ethereum
Arbitrum One is a layer 2: a network of its own that leans on Ethereum for its security. Transactions are ordered and executed on Arbitrum One, where they cost less. Their data is then posted to Ethereum in batches, so anyone can rebuild the state of Arbitrum One from Ethereum alone.
The design is called an optimistic rollup. Arbitrum One posts its results to Ethereum, and the results stand unless someone challenges them. A challenge is decided on Ethereum. Since February 2025 anyone can take part in this checking, not only a list of approved validators.
Three things follow from this design for a user.
- Fees are paid in ETH, the same coin as on Ethereum. A transaction on Arbitrum One usually costs far less than the same transaction on Ethereum.
- A withdrawal to Ethereum through the official bridge takes about a week. That is the window in which a result can still be challenged. Many third-party bridges pay out much sooner from their own funds and wait out the week themselves.
- One company still orders the transactions. The sequencer of Arbitrum One is run by Offchain Labs. The sequencer can delay a transaction but cannot forge one, and after about 24 hours anyone can force a transaction in through Ethereum.
Arbitrum One vs Arbitrum Nova
Arbitrum Nova is a second network of the same family. Nova opened on 9 August 2022 for applications with many small transactions, such as games and social apps. Nova differs from Arbitrum One in one place: where the transaction data is kept.
| Feature | Arbitrum One | Arbitrum Nova |
|---|---|---|
| Design | optimistic rollup | AnyTrust |
| Transaction data | posted to Ethereum in full | kept by a committee of seven; Ethereum receives a signed certificate |
| What you trust | that at least one honest party checks the results | the same, and that at least two committee members are honest |
| Chain ID | 42161 | 42170 |
| Fees paid in | ETH | ETH |
| Governed by | the Arbitrum DAO | the Arbitrum DAO |
| Open since | 31 August 2021 | 9 August 2022 |
If the committee of Nova fails to sign within a few minutes, Nova falls back to posting the full data to Ethereum, as Arbitrum One does. Nova pays for its lower fees with one more party to trust.
The two networks are separate. A token on Nova is not on Arbitrum One, even at the same address. An address looks the same on Arbitrum One, on Nova and on Ethereum, so a wallet accepts an address on the wrong network without complaint. That is how funds go astray.
What ARB is, and what it is not
ARB is the governance token of the Arbitrum DAO. Holders of ARB vote, or delegate their votes, on changes to Arbitrum One and Nova and on the spending of the DAO treasury. They also elect the Security Council: twelve members who can act quickly in an emergency.
ARB is not needed to use Arbitrum. Fees on Arbitrum One and Nova are paid in ETH, and an account with no ARB at all can use every application on both networks.
ARB was created with a supply of 10 billion tokens, and its distribution began with an airdrop in March 2023. The Arbitrum DAO may add at most 2 per cent a year, and only by a vote. Which part of a supply circulates is a separate number: see how to read a token’s supply.
Arbitrum chains: the rest of the family
Anyone can launch a network of their own with the same technology. Such networks were called Orbit chains; the Arbitrum documentation now calls them Arbitrum chains. A chain of this kind settles either to Ethereum, as a layer 2, or to Arbitrum One or Nova, as a layer 3.
The Arbitrum DAO governs Arbitrum One and Nova and no other chain. Each Arbitrum chain has its own operator and its own rules. A network built with Arbitrum technology is not Arbitrum One, and its rules are set by whoever runs it.
How to check which network you are on
- 01
Look at the chain ID
Every network has its own number. Arbitrum One is 42161, Arbitrum Nova is 42170, and Ethereum is 1. A wallet shows the number in its network settings.
- 02
Read the full network name before you send
A withdrawal page that offers Arbitrum One and Arbitrum Nova side by side is asking you to choose. If the page says only Arbitrum, check the chain ID or the explorer it links to.
- 03
Send a small amount first
A first transfer of a few dollars shows that the network and the address are right. It costs one more fee.
Arbitrum is the family, Arbitrum One is the network most apps mean, and ARB is the vote. Fees on both Arbitrum networks are paid in ETH.
Common questions
Is Arbitrum a layer 2?
Arbitrum One and Arbitrum Nova are layer 2 networks on Ethereum. Some Arbitrum chains are layer 3: they settle to Arbitrum One or Nova instead of Ethereum.
Do I need ARB to pay fees on Arbitrum?
No. Fees on Arbitrum One and Nova are paid in ETH. ARB is used to vote in the Arbitrum DAO.
Is Arbitrum One part of Ethereum?
No. Arbitrum One is a separate network with its own chain ID, 42161. It posts its transaction data to Ethereum, and funds move between the two networks through a bridge.
What is Arbitrum used for?
For the same things as Ethereum, at lower fees: trading, lending, stablecoin payments and games. Contracts written for Ethereum run on Arbitrum One with few changes or none.
Who controls Arbitrum One?
The Arbitrum DAO decides by votes of ARB holders, and a Security Council of twelve can act in an emergency. Offchain Labs runs the sequencer, which orders the transactions.
How Assetrix does it
Assetrix is a protocol on Arbitrum One. It issues ASTRX, a token backed by collateral, whose mint price is set by the contract and never falls. The backing of ASTRX is external collateral, never the protocol’s own token: stablecoins from the start, other currencies only once woken or voted in.
Assetrix is non-custodial. Collateral is held in the contract, never by a person or a company, and no one can stop its owner from reclaiming it. The Assetrix contract is immutable: it has no upgrade path and no wind-up procedure. Holders vote on a fixed set of parameters, and on nothing else.
Read next
Is a contract really immutable?
A claim that can be checked in a few minutes, and the four places where it usually turns out to be untrue.
How to tell whether a team can still change the contract
What to look for, in what order, and what each answer actually means.
How to read a token’s supply
Circulating, total, fully diluted — three numbers that are routinely confused, and what each one actually tells you.