The chain

Primcast is an Arbitrum Orbit chain running Nitro with ArbOS 61 ("Elara"). It is a rollup: every batch of transactions is posted to Ethereum, and the resulting state can be challenged there. This page explains what that means in practice.

Topology

                         Ethereum (L1)
   ┌──────────────────────────────────────────────────────────────┐
   │ RollupCore · Bridge · Inbox · SequencerInbox · Outbox          │
   │ ChallengeManager · UpgradeExecutor (chain owner) · token bridge │
   └──────▲──────────────────▲──────────────────────▲──────────────┘
          │ blobs (EIP-4844) │ assertions / stakes  │ delayed messages / deposits
   ┌──────┴───────┐   ┌──────┴────────┐    ┌────────┴────────────┐
   │ batch poster │   │ validator(s)  │    │ compliance sentinel │
   └──────▲───────┘   └──────▲────────┘    └────────▲────────────┘
          │                  │                      │
   ┌──────┴──────────────────┴──────────────────────┴─────────────┐
   │        Primcast sequencer (Nitro, ArbOS 61, 100 ms blocks)     │
   │        address filter + event filter (compliance)              │
   └──────▲─────────────────────────────────────────────▲─────────┘
          │ users, wallets, dapps                       │ restricted list (S3)
   ┌──────┴──────┐                               ┌──────┴───────────┐
   │  full nodes │  explorer, indexers           │ compliance       │ ◄── IdentityRegistry sanctions
   └─────────────┘                               │ publisher        │
                                                 └──────────────────┘

Block production

• One sequencer, operated by Primcast. It orders transactions first come, first served, and produces a block every 100 ms.
• Private mempool. Pending transactions are not broadcast, so other users cannot front-run or sandwich them. The sequencer operator, however, does see order flow. Its ordering policy is a commitment, not a cryptographic guarantee.
• Soft confirmation is immediate. A wallet sees its transaction included within about 100 ms. That confirmation comes from the sequencer until the batch is posted to Ethereum.

Data availability

• Rollup mode (default): every batch is posted to Ethereum as blob data. Anyone can reconstruct the chain from Ethereum alone.
• AnyTrust mode (optional): data is held by a Data Availability Committee and only a certificate goes to Ethereum. This is cheaper, but it adds the assumption that the committee stays honest and available. The mode in use on each network is listed under Network parameters.

Validation and fraud proofs

Validators run the chain's state transition and post assertions to Ethereum with a stake. An incorrect assertion can be challenged, and the challenge is settled on Ethereum. At launch the validator set is an allow-list chosen by governance. It can later be opened up, including to permissionless BoLD validation. Until then, security depends on at least one honest allow-listed validator.

Finality

Deposits and withdrawals

• Bridge: the canonical Arbitrum token bridge between Ethereum and Primcast carries ETH, USDC, USDT, WETH and other standard ERC-20s. Primcast runs no custom bridge.
• Deposits arrive in minutes, once the deposit message is included.
• Withdrawals to Ethereum can be executed only after the challenge period, so plan for about a week. Third-party liquidity providers can offer faster exits for a fee; Primcast does not.

Censorship resistance

If the sequencer ignores a transaction, the user can submit it through the Ethereum Inbox (the delayed inbox). After 24 hours it can be force-included regardless of the sequencer.

Gas and fees

• Gas is paid in ETH. A transaction pays for L2 execution plus the cost of posting its data to Ethereum.
• Governance sets the minimum L2 base fee and speed limit through the chain owner.
• Tools that simulate gas locally, such as Foundry's forge script, do not model the L1 data cost. On any Arbitrum chain, broadcast with --skip-simulation --slow. See Fees and the developer guide.

Chain governance

The rollup's owner is Arbitrum's UpgradeExecutor, and executor rights belong to the Primcast Safe. Through it governance can upgrade ArbOS and the core contracts, change fee parameters, add or remove validators and batch posters, and manage the compliance filterer. The same Safe owns the application contracts. See Trust & security.

Parameters

Endpoints and live contract addresses are on the Network page.