Arc mainnet is live: what changed

2026-09-16

Arc public mainnet opened on 16 September 2026, on the date Circle announced for it six weeks earlier. The network answered on the day: a public RPC returns chain id 0x13b2, which is 5042, and blocks arrive about every half second. This page is the event – what was announced, what actually appeared, and what is still missing. For the network as it runs, read the Arc blockchain guide.

What Circle announced, and when

Two Circle-owned documents carried the date, both published on 5 August 2026. The Arc blog post, signed Team Arc, said Arc public mainnet would launch on 16 September 2026. The Circle press release of the same date (Circle Internet Group, Inc., NYSE: CRCL) was more careful with its tense: it described Arc as then in private mainnet with more than 100 ecosystem and institutional builders, and on track for a public launch on that day, with the usual hedge that Arc features may be modified, delayed or cancelled at any time without notice. The date held. Both documents also described a product suite around the network: an app framework for onchain workflows, AI-assisted build tools, and tooling for tokenised real-world assets.

Status: what a check on 16 September 2026 showed

Checked 16 September 2026	What it showed
Live node check, 2026-09-16T10:08Z	the public mainnet RPC answered eth_chainId with `0x13b2`, which is 5042; four documented mirrors and one independent endpoint answered the same
Block production	about half a second per block, with a 30M block gas limit
Gas	USDC, EIP-1559, the 20 gwei base-fee floor held and rose to about 31 gwei under load
Circle CCTP	Arc carries domain 26, with TokenMessengerV2 and MessageTransmitterV2 deployed
Uniswap	the canonical Uniswap Labs v3 contracts are deployed, and live pools quote against the 6-decimal USDC face
Block explorer	none a reader could open on the day: the one host Circle names answered a Circle SSO login on every path, its API included. Re-checked 17 September 2026: the wall is gone and the same host now serves an ordinary public explorer
The testnet	chain 5042002 is a separate network and nothing published says it is being retired

Read a negative row as a negative result, not as proof of absence: the probe ran from one network, so a host that did not answer may still exist. The defensible sentence is the narrow one. The explorer row is what that device is for: it read “none a reader can open” as of 2026-09-16T10:08Z, and a re-check on 17 September 2026 turned the negative into a positive. A dated negative that later becomes a positive is the device working, not the page having been wrong.

What "public mainnet" means here

It was not a first block. Arc had been running a private mainnet with more than 100 ecosystem and institutional builders, and 16 September opened that network rather than starting a new one. The operator differs from the testnet's, which is the part most summaries miss: the testnet is offered by Circle Technology Services, LLC, while the mainnet L1 is described as launched by Arc Network Services LLC and operated by a permissioned validator set.

Who secures it

Circle named a founding validator cohort alongside itself: BlackRock, DTCC, Galaxy, Global Payments, ICE, Mastercard, MoneyGram, SBI Group, Standard Chartered, Sumitomo Corporation and Visa – eleven institutions plus Circle, on a permissioned set. Treat that list as the announced cohort and not as a roll call of who is signing blocks today; Circle has published no per-validator status page.

The day-one ecosystem was announced the same way: Aave, Aerodrome, FalconX, Galaxy, GSR, Keyrock, Morpho, Nonco, Uniswap and XFX among DeFi protocols and capital allocators; Rain, Thunes and Wirex in stablecoin payments; Binance Wallet, Chainlink, Fireblocks, Kraken, Ledger, MetaMask, Uniswap Labs and Upbit among exchanges and wallet providers. One correction, because at least one news aggregator got it wrong: Fireblocks sits in that last group, not in the validator cohort. Of those names the one that is verifiably on chain today is Uniswap. Institutional integrations are further out – BlackRock is expected to deploy BUIDL on Arc, and Circle describes work with DTCC on tokenising DTC-custodied assets beginning in the second half of 2027.

What changed against the testnet you used

Chain id. Arc mainnet is 5042 (hex 0x13b2). Arc Testnet stays 5042002 (hex 0x4cef52) and is a different network: an address funded there has no balance here, and a contract deployed there has no code here. The community registries that reserved 5042 under the name Arc before the launch turned out to have it right, but the reason to trust it now is that the node answers with it. Mind the homonym in those registries: ids 1243 and 1244, labelled ARC Mainnet and ARC Testnet, belong to Archie Chain and are both marked deprecated.
RPC. Circle publishes a mainnet endpoint at rpc.mainnet.arc.io with three documented mirrors; the guide lists them. Third-party endpoints circulated before the launch and some were wrong. The only test that settles an endpoint is asking it for its chain id.
The explorer arrived a day late. This is the one thing the mainnet opened without: the single host Circle names was gated behind Circle's own SSO on every path, so on the day there was no public block explorer and no explorer API to verify contracts against. It lasted one day – on 17 September 2026 that same host began answering anonymous readers, and contracts verify against it. The guide carries the address; lookalike domains are still circulating, and are still a phishing risk.
The faucet. It stays a testnet faucet: mainnet USDC is real money and has none. Circle has published nothing about retiring the Arc testnet or its faucet, so do not plan around it disappearing either.
Gas. USDC pays for gas in both environments, and the numbers that were documented as testnet parameters turned out to describe the mainnet too: the 20 gwei base-fee floor held on the day, and the base fee rose to about 31 gwei under launch-day load. Circle's design target of roughly $0.01 per transaction is an aim, not a quote – read the fee from the node.
The bridge. Circle's CCTP now carries Arc at domain 26, so USDC burns on a supported chain and mints here. A second route, the intent bridge Relay, lists Arc with deposits enabled and covers the chains and assets CCTP does not.

What changed for a launch on arc.openfair.app

This site is now the mainnet deployment: chain id 5042, a 0.5 USDC creation fee and a 10000 USDC bonding-curve target, all in real USDC. Every launch here is a mainnet launch, and every amount on the site means what it says.

The dependency that used to block this is gone. openfair's contracts need a Uniswap V3-compatible position manager, factory and router, and the canonical Uniswap Labs v3 deployment is on Arc. What it does NOT need, and what Arc does not have, is an 18-decimal wrapper of the native coin: USDC on Arc is 18-decimal at the EVM level and 6-decimal through its ERC-20 face, one balance at two scales, and Circle says no wrapped USDC is coming. So the contracts running here are the same lineage as the Stable deployment – the one built for a 6-decimal quote asset – rather than the generation the other chains run. One feature is off on Arc as a result: launches paired with a tokenised asset, which belong to that other generation and need a 6-decimal port before they can run. The soft-cap crowd launch was the second one on the day, and stopped being one a day later: the stable lineage has its own crowd contracts – a 25-field create with no quote asset at all, native because the coin here is the unit a raise collects – and they were broadcast on Arc on 17 September 2026, so a crowd launch runs here from that date. Like the explorer row above, that is a dated negative turning into a positive, not a page that was wrong. Contract verification goes to two independent targets: the chain's own block explorer, and Sourcify, which supports chain 5042. You can launch on Arc today and read how a launch works.

How to check any of this yourself

Three questions settle the network. Does the endpoint you were handed answer eth_chainId, and with which number? Does eth_gasPrice agree with the fee you were quoted? And does the contract you are about to trade actually exist at that address – eth_getCode, not a screenshot? A chain id, an RPC host or a domain number published by anyone other than Circle is a claim until the node agrees with it, and that was as true on the day the mainnet opened as it was the week before.

FAQ

Is Arc mainnet live?

Yes, since 16 September 2026. The public RPC answers with chain id 5042, blocks arrive roughly every half second, CCTP carries USDC in at domain 26 and Uniswap v3 is deployed. The one thing the mainnet opened without was a public block explorer; that arrived a day later, on 17 September 2026.

What is the Arc mainnet chain id?

5042, hex 0x13b2, read from the node at 2026-09-16T10:08Z. Arc Testnet is a separate network at 5042002, hex 0x4cef52. Read the id from the node with eth_chainId before you sign anything, on either network.

Is there an ARC token or an airdrop now that mainnet is open?

Nothing announced, and gas is USDC in every document. The ARC whitepaper post of 11 May 2026 describes a proposed coordination asset for staking, governance and fee mechanics, and states that ARC is not launched. No Circle or Arc page announces a token launch, a distribution or an airdrop. A token claiming to be it, on Arc or anywhere else, is not one.

Can I bridge USDC into Arc mainnet?

Yes. Circle's CCTP supported-chains table now carries an Arc row at domain 26, so USDC burns on a chain CCTP serves and mints here with nobody in between. Relay is the other route and reaches chains and assets CCTP does not. Our bridging page and the Arc blockchain guide cover both.