| 2026-07-08 | Upgrade 19: Karst hard fork | Karst: the L2 Contract Manager (L2CM), CANNON_KONA promoted to the respected game type, a subset of Osaka EIPs on L2, and a preemptive BN256 pairing input-size reduction. |
| 2026-06-26 | Deprecation of Req/Res CL P2P sync | Retirement of the op-node request-response consensus-layer P2P sync client in favor of syncing through the execution client. Removed in op-node/v1.19.1. |
| 2026-05-31 | End of Support for op-geth and op-program | End of support for op-geth and op-program, neither of which supports Karst. Migrate execution to op-reth and fault proofs to kona-client. |
| 2026-05-26 | Stake-based priority ordering on OP Mainnet | A time-boxed OP Mainnet experiment giving stakers in the PolicyEngineStaking contract priority in transaction ordering, capped at four weeks. |
| Not dated | Deprecation of op-deployer upgrade and manage commands | op-deployer manage retired, and op-deployer upgrade capped at op-contracts/v5.0.0. L1 contract upgrades beyond that use superchain-ops or OPCM directly. Postdates op-contracts/v6.0.0. |
| Not dated | Upgrade 18: Cannon + Kona and Custom Gas Token v2 | Contract-only upgrade adding the CANNON_KONA (8) game type alongside CANNON (0), Custom Gas Token v2, and the creator-pattern dispute game refactor. Shipped in op-contracts/v6.0.0 (released 2026-03-16). |
| 2025-12-03 | Fusaka upgrade notice | Readiness work so OP Stack chains keep deriving from an L1 that has activated Fusaka and its blob parameter-only forks. Not Fusaka adoption on L2. |
| 2025-12-02 | Upgrade 17: Jovian hard fork | Jovian: a configurable minimum base fee, the data-availability footprint block limit, and Cannon support for Go 1.24. |
| 2025-10-02 | Upgrade 16a | Maintenance contract upgrade superseding Upgrade 16: removes the unused interop withdrawal-proving code and adds SystemConfig feature toggles. |
| 2025-07-24 | Upgrade 16: preparing for interop | Contract upgrade making OptimismPortal interop-ready, meeting updated Stage 1 requirements, adding Go 1.23 support in Cannon, and raising MAX_GAS_LIMIT to 500M. Invalidated existing withdrawal proofs. |
| 2025-05-14 | Superchain withdrawal pause test | A scheduled exercise of the Superchain-wide pause and unpause incident-response path. No user or operator action was required. |
| 2025-05-09 | Upgrade 15: Isthmus hard fork | Isthmus: Prague features on the OP Stack, the L2 withdrawals root in the block header, and the operator fee. |
| Not dated | Upgrade 14: MT-Cannon and Isthmus L1 contracts | Contract upgrade shipping multithreaded 64-bit Cannon (MT-Cannon) and the Isthmus L1 contracts. Shipped in op-contracts/v3.0.0 (released 2025-05-08); the notice’s own mainnet date was an estimate. |
| Not dated | L1 Pectra user fees and chain profitability | How the EIP-7623 gas repricing at L1 Pectra affected chains still posting data as calldata rather than blobs, and which Ecotone scalars to check. |
| 2025-04-02 | Upgrade 13: OPCM and incident response | Contract upgrade introducing the OP Contracts Manager (OPCM), fault-proof incident response improvements, and the DeputyPauseModule. |
| 2025-03-20 | Superchain testnets’ blob fee bug | A testnet-only blob base fee miscalculation that overcharged L1 fees, and the hardfork activation that fixed it. Mainnet chains were never affected. |
| Not dated | Preparing for Pectra breaking changes | Breaking changes for chain and node operators when Pectra activated on L1. The page carries only tentative L1 slot times that were later superseded; it was last revised 2025-03-11. |
| 2025-01-09 | Preparing for Holocene breaking changes | Holocene: stricter block derivation, EIP-1559 parameters made configurable through SystemConfig, and the MIPS contract upgrade. |
