> For the complete documentation index, see [llms.txt](https://docs.megaeth.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.megaeth.com/spec/system-contracts/overview.md).

# Overview

This page specifies the system-contract registry and the protocol-level rules that apply to system contracts in MegaETH. It defines the system-contract set.

## Specification

### Distinction from Precompiles

Both [precompiles](/spec/megaevm/precompiles.md) and system contracts reside at fixed addresses and provide protocol-level functionality, but they differ in a fundamental way:

* **Precompiles** are stateless and pure. They perform a deterministic computation on their input and return output without reading or writing on-chain state. The EVM handles precompile calls entirely outside normal bytecode execution.
* **System contracts** are stateful. They have deployed bytecode, maintain persistent storage, and participate in normal EVM state access (including `SLOAD`, `SSTORE`, and account balance). Some of their functions are subject to [call interception](/spec/system-contracts/interception.md) for protocol-level side effects, but the contracts themselves exist as ordinary accounts with code and storage.

### Stable Registry

A node MUST recognize the following contracts as system contracts:

| Contract                                                                       | Address                            | Since                                        | Purpose                                    |
| ------------------------------------------------------------------------------ | ---------------------------------- | -------------------------------------------- | ------------------------------------------ |
| [Oracle](/spec/system-contracts/oracle.md)                                     | `ORACLE_CONTRACT_ADDRESS`          | [MiniRex](/spec/network-upgrades/minirex.md) | Off-chain data key-value storage           |
| [High-Precision Timestamp](/spec/system-contracts/high-precision-timestamp.md) | `HIGH_PRECISION_TIMESTAMP_ADDRESS` | [MiniRex](/spec/network-upgrades/minirex.md) | Sub-second timestamp oracle service        |
| [KeylessDeploy](/spec/system-contracts/keyless-deploy.md)                      | `KEYLESS_DEPLOY_ADDRESS`           | [Rex2](/spec/network-upgrades/rex2.md)       | Deterministic cross-chain deployment       |
| [MegaAccessControl](/spec/system-contracts/mega-access-control.md)             | `MEGA_ACCESS_CONTROL_ADDRESS`      | [Rex4](/spec/network-upgrades/rex4.md)       | Volatile-data access control               |
| [MegaLimitControl](/spec/system-contracts/mega-limit-control.md)               | `MEGA_LIMIT_CONTROL_ADDRESS`       | [Rex4](/spec/network-upgrades/rex4.md)       | Query remaining compute-gas budget         |
| [SequencerRegistry](/spec/system-contracts/sequencer-registry.md)              | `SEQUENCER_REGISTRY_ADDRESS`       | [Rex5](/spec/network-upgrades/rex5.md)       | System address and sequencer role registry |

### Deployment Semantics

System contracts MUST be available at their specified addresses when the corresponding spec is active. Their availability is gated by [spec](/spec/hardfork-spec.md) activation.

The code hash stated on each contract page is the normative identity of that contract version. The artifact JSON linked on each page is the canonical source of the full deployed bytecode.

### Call Interception

Some system-contract functions are handled at the EVM level rather than exclusively by contract bytecode. The generic interception mechanism — when it fires, how selectors are matched, how calls that do not match fall through to bytecode, and the gas and call-scheme rules — is specified on the [Call Interception](/spec/system-contracts/interception.md) page.

Each system-contract page defines which of its functions are intercepted and what each interception does:

* [Oracle — `sendHint`](/spec/system-contracts/oracle.md#hint-forwarding): performs a side effect (hint forwarding), then falls through to bytecode.
* [KeylessDeploy — `keylessDeploy`](/spec/system-contracts/keyless-deploy.md#interception-scope): intercepted at depth 0; executes deployment in a sandbox instead of on-chain bytecode.
* [MegaAccessControl](/spec/system-contracts/mega-access-control.md#interception-scope): all three functions are fully intercepted.
* [MegaLimitControl](/spec/system-contracts/mega-limit-control.md#interception-scope): `remainingComputeGas` is fully intercepted.

### Backward Compatibility Rule

Any change to system-contract semantics, bytecode-visible interface behavior, or interception rules MUST be introduced by a new spec. Stable behavior for an already-activated spec MUST remain unchanged.

## Constants

| Constant                           | Value                                        | Description                                     |
| ---------------------------------- | -------------------------------------------- | ----------------------------------------------- |
| `ORACLE_CONTRACT_ADDRESS`          | `0x6342000000000000000000000000000000000001` | Stable Oracle system-contract address           |
| `HIGH_PRECISION_TIMESTAMP_ADDRESS` | `0x6342000000000000000000000000000000000002` | Stable high-precision timestamp wrapper address |
| `KEYLESS_DEPLOY_ADDRESS`           | `0x6342000000000000000000000000000000000003` | Stable KeylessDeploy system-contract address    |
| `MEGA_ACCESS_CONTROL_ADDRESS`      | `0x6342000000000000000000000000000000000004` | MegaAccessControl address                       |
| `MEGA_LIMIT_CONTROL_ADDRESS`       | `0x6342000000000000000000000000000000000005` | MegaLimitControl address                        |
| `SEQUENCER_REGISTRY_ADDRESS`       | `0x6342000000000000000000000000000000000006` | SequencerRegistry address                       |

## Spec History

* [MiniRex](/spec/network-upgrades/minirex.md) introduced the Oracle and High-Precision Timestamp contracts.
* [Rex2](/spec/network-upgrades/rex2.md) introduced KeylessDeploy.
* [Rex4](/spec/network-upgrades/rex4.md) — added MegaAccessControl and MegaLimitControl contracts.
* [Rex5](/spec/network-upgrades/rex5.md) — added SequencerRegistry; upgraded Oracle to v2.0.0 (dynamic authority).


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