> ## Documentation Index
> Fetch the complete documentation index at: https://docs.base.org/llms.txt
> Use this file to discover all available pages before exploring further.

# Isthmus

> Overview of the Isthmus hardfork, incorporating Ethereum Pectra EIPs and introducing the operator fee mechanism for sequencer revenue.

## Activation Timestamps

| Network   | Activation timestamp                   |
| --------- | -------------------------------------- |
| `mainnet` | `1746806401` (2025-05-09 16:00:01 UTC) |
| `sepolia` | `1744905600` (2025-04-17 16:00:00 UTC) |

## Execution Layer

* [Pectra](https://eips.ethereum.org/EIPS/eip-7600) (Execution Layer):
  * [EIP-7702](https://eips.ethereum.org/EIPS/eip-7702)
    * [Span Batch Updates](/base-chain/specs/upgrades/isthmus/derivation#span-batch-updates)
  * [EIP-2537](https://eips.ethereum.org/EIPS/eip-2537)
  * [EIP-2935](https://eips.ethereum.org/EIPS/eip-2935)
    * [EIP-2935 Contract Deployment](/base-chain/specs/upgrades/isthmus/derivation#eip-2935-contract-deployment)
  * [EIP-7002](https://eips.ethereum.org/EIPS/eip-7002)
    * The EIP-7002 predeploy contract and syscall are not adopted as part of Base.
  * [EIP-7251](https://eips.ethereum.org/EIPS/eip-7251)
    * The EIP-7251 predeploy contract and syscall are not adopted as part of Base.
  * [EIP-7623](https://eips.ethereum.org/EIPS/eip-7623)
  * [EIP-6110](https://eips.ethereum.org/EIPS/eip-6110)
  * [EIP-7685](https://eips.ethereum.org/EIPS/eip-7685)
* [L2ToL1MessagePasser Storage Root in Header](/base-chain/specs/upgrades/isthmus/exec-engine#l2tol1messagepasser-storage-root-in-header)
* [Operator Fee](/base-chain/specs/upgrades/isthmus/exec-engine#operator-fee)

## Consensus Layer

* [Isthmus Derivation](/base-chain/specs/upgrades/isthmus/derivation)

## Smart Contracts

* [Predeploys](/base-chain/specs/upgrades/isthmus/predeploys)
* [L1 Block Attributes](/base-chain/specs/upgrades/isthmus/l1-attributes)
* [System Config](/base-chain/specs/upgrades/isthmus/system-config)