> ## Documentation Index > Fetch the complete documentation index at: https://docs.optimism.io/llms.txt > Use this file to discover all available pages before exploring further. # Smart Contract overview > Learn about the smart contracts that make up the OP Stack. export const NormativeSpec = ({what, title, href, note}) => Normative spec: {what} is normatively defined in the{" "} {title}. {note} ; The OP Stack's onchain logic lives in two groups of smart contracts: the Layer 1 contracts deployed to Ethereum, and the Layer 2 predeploys that exist in every OP Stack chain's genesis state. This page explains what each group is for and routes you to the canonical definition of each contract. It does not restate interfaces, parameters, or per-release versions: * **Behavior** is defined in the [OP Stack specifications](https://specs.optimism.io/?utm_source=op-docs\&utm_medium=docs). * **Source code** lives in [`packages/contracts-bedrock`](https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock) in the monorepo, with generated interface documentation at [devdocs.optimism.io](https://devdocs.optimism.io/contracts-bedrock). * **Deployed addresses** are on the [OP Mainnet addresses page](/op-mainnet/network-information/op-addresses), sourced from the [superchain-registry](https://github.com/ethereum-optimism/superchain-registry). ## Layer 1 contracts The L1 contracts hold the chain's bridge liquidity, accept deposits, verify withdrawals, store the chain's configuration, and adjudicate output proposals through the fault proof system. The [Optimism Overview specification](https://specs.optimism.io/protocol/overview.html?utm_source=op-docs\&utm_medium=docs#core-l1-smart-contracts) includes an architecture diagram showing how they connect. ### Bridging and messaging Deposits enter the chain and withdrawals leave it through a layered stack: the `OptimismPortal` is the low-level deposit and withdrawal contract, the `L1CrossDomainMessenger` adds replayable message passing on top of it, and the token bridges sit on top of the messenger. Messages sent directly to the `OptimismPortal` are not replayable, so users and app developers should prefer the messenger or bridge interfaces. | Contract | Role | Normative spec | | ------------------------ | -------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `OptimismPortal` | Low-level deposit entry point and withdrawal exit; withdrawals are proven and finalized against dispute game results | [Deposits](https://specs.optimism.io/protocol/deposits.html?utm_source=op-docs\&utm_medium=docs#deposit-contract), [Withdrawals](https://specs.optimism.io/protocol/withdrawals.html?utm_source=op-docs\&utm_medium=docs#the-optimism-portal-contract), [OptimismPortal fault proof integration](https://specs.optimism.io/fault-proof/stage-one/optimism-portal.html?utm_source=op-docs\&utm_medium=docs) | | `ETHLockbox` | Escrows the ETH deposited through authorized portals, so ETH liquidity can be managed and migrated as a unit | [ETH Lockbox](https://specs.optimism.io/interop/eth-lockbox.html?utm_source=op-docs\&utm_medium=docs) | | `L1CrossDomainMessenger` | Replayable cross-domain message passing between L1 and L2; the recommended messaging interface | [Cross Domain Messengers](https://specs.optimism.io/protocol/messengers.html?utm_source=op-docs\&utm_medium=docs) | | `L1StandardBridge` | ETH and ERC-20 bridging built on the messenger; escrows L1-native tokens | [Standard Bridges](https://specs.optimism.io/protocol/bridges.html?utm_source=op-docs\&utm_medium=docs) | | `L1ERC721Bridge` | ERC-721 bridging built on the messenger; escrows L1-native NFTs | [Standard Bridges](https://specs.optimism.io/protocol/bridges.html?utm_source=op-docs\&utm_medium=docs) | The standard bridge is not intended to support every ERC-20 variant. Tokens with transfer fees, rebasing logic, or blocklists may not work correctly. See [Standard Bridge](/app-developers/guides/bridging/standard-bridge) for guidance. ### Chain configuration | Contract | Role | Normative spec | | ------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------- | | `SystemConfig` | Per-chain configuration (batcher, gas, fee scalars) read by the derivation pipeline, plus the onchain registry of the chain's other contract addresses | [System Config](https://specs.optimism.io/protocol/system-config.html?utm_source=op-docs\&utm_medium=docs) | | `SuperchainConfig` | Superchain-wide configuration and the Guardian's pause mechanism; pauses are scoped by an identifier and expire automatically | [Superchain Configuration](https://specs.optimism.io/protocol/superchain-config.html?utm_source=op-docs\&utm_medium=docs) | ### Proposals and fault proofs Claims about the L2 state are proposed and challenged permissionlessly through dispute games rather than trusted output submission. See the [fault proofs explainer](/op-stack/fault-proofs/explainer) for how the system works end to end. | Contract | Role | Normative spec | | ------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `DisputeGameFactory` | Deploys and tracks dispute game instances; the entry point for proposing L2 state | [Dispute Game Interface](https://specs.optimism.io/fault-proof/stage-one/dispute-game-interface.html?utm_source=op-docs\&utm_medium=docs#disputegamefactory-interface) | | `FaultDisputeGame` | Adjudicates a claim about L2 state through a bisection game backed by an onchain fault proof VM | [Fault Dispute Game](https://specs.optimism.io/fault-proof/stage-one/fault-dispute-game.html?utm_source=op-docs\&utm_medium=docs) | | `PermissionedDisputeGame` | A `FaultDisputeGame` variant restricting participation to a designated proposer and challenger; used where stricter access control is required | [Fault Dispute Game](https://specs.optimism.io/fault-proof/stage-one/fault-dispute-game.html?utm_source=op-docs\&utm_medium=docs) | | `AnchorStateRegistry` | Tracks anchor states (recent, unchallenged starting points for new games) and the validity of game results | [AnchorStateRegistry](https://specs.optimism.io/fault-proof/stage-one/anchor-state-registry.html?utm_source=op-docs\&utm_medium=docs) | | `DelayedWETH` | Holds dispute bonds and delays payouts so bad resolutions can be caught before funds move | [Bond Incentives](https://specs.optimism.io/fault-proof/stage-one/bond-incentives.html?utm_source=op-docs\&utm_medium=docs#delayedweth) | | `MIPS64` | Onchain fault proof VM: a big-endian, 64-bit, multithreaded MIPS emulator that executes a single disputed instruction step | [Cannon Fault Proof VM](https://specs.optimism.io/fault-proof/cannon-fault-proof-vm.html?utm_source=op-docs\&utm_medium=docs) | | `PreimageOracle` | Serves the preimages of hashed inputs that the fault proof VM reads during a disputed step | [Pre-image Oracle](https://specs.optimism.io/fault-proof/index.html?utm_source=op-docs\&utm_medium=docs#pre-image-oracle) | ### Legacy and deprecated contracts * `AddressManager` is a legacy name-to-address registry from the pre-Bedrock system. It survives only because the `L1CrossDomainMessenger` still sits behind a legacy `ResolvedDelegateProxy` that resolves through it. * `L2OutputOracle` was the trusted output proposal contract before fault proofs. It is deprecated: output proposals are made through the `DisputeGameFactory` instead, per the [L2 output root proposals specification](https://specs.optimism.io/protocol/proposals.html?utm_source=op-docs\&utm_medium=docs). * `ProtocolVersions` signaled recommended and required protocol versions to node operators. The contract has been removed from the OP Stack contracts; the versioning scheme it exposed remains documented in the [Superchain Upgrades specification](https://specs.optimism.io/protocol/superchain-upgrades.html?utm_source=op-docs\&utm_medium=docs#protocol-version). ### Upgrading the contracts L1 contracts are upgraded through the [OP Contracts Manager (OPCM)](/chain-operators/reference/opcm), which deploys and upgrades the L1 contracts as a versioned set. The [superchain-ops](/chain-operators/tutorials/l1-contract-upgrades/superchain-ops-guide) workflow drives OPCM under the hood and is the path for chains that require Security Council signing; other chains can call OPCM directly. `op-deployer` remains the tool for initial deployments, but its upgrade command is deprecated in favor of OPCM; see the [deprecation notice](/notices/op-deployer-upgrade-deprecation). L2 predeploys are upgraded through the L2 Contract Manager (L2CM), introduced in [Upgrade 19](/notices/upgrade-19). At a network upgrade, the consensus layer emits a network upgrade transaction that has the L2 `ProxyAdmin` delegatecall the `L2ContractsManager` contract, which updates every predeploy implementation in a single atomic transaction, replacing the older practice of per-contract multisig transactions. See the [L2 Contract Manager feature page](/op-stack/features/l2-contract-manager) and the [L2 Upgrades specification](https://specs.optimism.io/protocol/l2-upgrades-1-execution.html?utm_source=op-docs\&utm_medium=docs). ### Contract releases Contracts are released as tagged monorepo releases named `op-contracts/vX.Y.Z`, following the documented [versioning policy](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/book/src/policies/versioning.md). This page does not track releases; use these sources instead: * The [op-contracts release history](/releases/op-contracts) lists every release with its notes, generated from the GitHub releases. * The [superchain-registry standard versions](https://github.com/ethereum-optimism/superchain-registry/tree/main/validation/standard) files record the exact contract versions and implementation addresses that make up each standard release. * The [network upgrades registry](/op-stack/protocol/network-upgrades) maps each hardfork to its governance approval and required component versions. Releases tagged `v` without a component name (for example `v1.1.4`) are Go code releases and do not include smart contracts. Only deploy contracts from `op-contracts/vX.Y.Z` tags. ## Layer 2 contracts (predeploys) Predeploys are contracts placed at fixed, well-known addresses in the genesis state of every OP Stack chain. Unlike precompiles they are ordinary EVM contracts, which keeps them portable across client implementations and visible to standard tooling. Most live in the `0x4200000000000000000000000000000000000xxx` address namespace and sit behind proxies owned by the L2 `ProxyAdmin`. The [Predeploys specification](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs) is the canonical list: it maintains the full table of predeploy addresses, the upgrade each was introduced in, deprecation status, and whether each is proxied, along with the normative definition of each contract. ### Bridging predeploys The L2 side mirrors the L1 bridging stack. The [`L2CrossDomainMessenger`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#l2crossdomainmessenger) is the recommended high-level messaging interface, the [`L2ToL1MessagePasser`](https://specs.optimism.io/protocol/withdrawals.html?utm_source=op-docs\&utm_medium=docs#the-l2tol1messagepasser-contract) records withdrawal messages whose inclusion is later proven on L1, and the [`L2StandardBridge`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#l2standardbridge) and `L2ERC721Bridge` pair with their L1 counterparts. The [`OptimismMintableERC20Factory`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#optimismmintableerc20factory) and `OptimismMintableERC721Factory` permissionlessly create the L2 token contracts that the bridges mint and burn. Do not bridge an ERC-721 that was originally deployed on an OP Stack chain through the ERC-721 bridge; it only supports NFTs originally deployed on L1. ### Fee and system predeploys * The [`GasPriceOracle`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#gaspriceoracle) exposes the parameters and helper functions for estimating the data availability portion of the transaction fee. The exact fee formula changes across upgrades and is defined in the spec, not here; see [transaction fees](/op-stack/transactions/fees) for the explanation. * The [`L1Block`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#l1block) predeploy exposes information about the latest known L1 block, written by the protocol through a system deposit transaction. * The fee vaults ([`SequencerFeeVault`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#sequencerfeevault), [`BaseFeeVault`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#basefeevault), [`L1FeeVault`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#l1feevault), and, since the Isthmus upgrade, the [`OperatorFeeVault`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#operator-fee-vault)) collect the components of the transaction fee for withdrawal to configured recipients. See [fee vaults](/op-stack/transactions/fee-vaults) for operational details. * The [`ProxyAdmin`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#proxyadmin) owns the proxies of the other predeploys and controls their upgrades. * The [`BeaconBlockRoot`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#beacon-block-root) contract ([EIP-4788](https://eips.ethereum.org/EIPS/eip-4788)) exposes L1 beacon block roots, available since the Ecotone upgrade. * [`WETH9`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#weth9) is the standard Wrapped Ether contract at a deterministic address. ### GovernanceToken The [`GovernanceToken`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#governance-token) is the OP token used in Optimism governance, supporting voting and delegation. It is owned by a `MintManager` contract that enforces the token inflation schedule. See the [governance resources](/governance/resources) for how the token is used. ### EAS (Ethereum Attestation Service) The [`EAS`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#eas) and [`SchemaRegistry`](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs#schemaregistry) predeploys implement the [Ethereum Attestation Service](https://attest.sh/) protocol, an open-source public good for issuing and managing onchain attestations. You can interact with EAS through the [EAS Scan UI](https://optimism.easscan.org/), the [EAS SDK](https://docs.attest.sh/docs/developer-tools/eas-sdk), or [directly onchain](https://github.com/ethereum-attestation-service/eas-contracts/blob/master/contracts/EAS.sol), and index attestations with the [EAS API](https://docs.attest.sh/docs/developer-tools/api) or the [open source indexer](https://github.com/ethereum-attestation-service/eas-indexing-service). See [attestations](/governance/eas-attestations) for how attestations are used in Optimism governance. ### Deprecated predeploys The `LegacyMessagePasser`, `DeployerWhitelist`, `LegacyERC20ETH`, and `L1BlockNumber` contracts remain in state for backwards compatibility with the pre-Bedrock system but are deprecated and unused. Their addresses and history are in the [Predeploys specification](https://specs.optimism.io/protocol/predeploys.html?utm_source=op-docs\&utm_medium=docs). ## Next steps * Read the [Optimism Overview specification](https://specs.optimism.io/protocol/overview.html?utm_source=op-docs\&utm_medium=docs) for the architecture diagrams connecting these contracts. * Browse the [contract source](https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock) and the [generated contract reference](https://devdocs.optimism.io/contracts-bedrock). * Look up [contract addresses on OP Mainnet](/op-mainnet/network-information/op-addresses). * Learn how the [fault proof system](/op-stack/fault-proofs/explainer) uses the dispute contracts.