Upgrade 18 - Custom Gas Token v2 and Kona Proofs

Executive Summary

At its core, U18 delivers three new advancements to the OP Stack:

1. Custom Gas Token v2 (CGT v2):

   A redesigned implementation that allows OP Stack chains to use any asset - not just ETH - as their native gas token. This unlocks economic alignment for diverse ecosystems, from stablecoin-based rollups offering predictable fees to governance-token-driven networks. CGT v2 emphasizes flexibility, minimal protocol footprint, and forward compatibility by decoupling native asset logic from the bridging layer.

   Note: Custom Gas Token v2 is a new implementation that is not compatible with legacy CGT chains. There is currently no migration path from legacy CGT to CGT v2.

2. Creator Pattern Dispute Game Refactor:

   Simplifies chain deployment by introducing clone-with-immutable-arguments (CWIA) for dispute game contracts. This change removes the need for chain-specific deployments, reducing operational overhead while preserving safety and upgradeability across chains, and reducing gas costs to ensure all operations stay below the EIP-7825 transaction gas limit cap.

3. Cannon + Kona:

   Adds a second, Rust-based fault proof implementation - Kona - to operate alongside Cannon, increasing redundancy and diversity in the fault proof layer. The new game type, CANNON_KONA, is registered but not yet set as the canonical proof type, ensuring a safe rollout path as the ecosystem transitions toward full permissionless fault proofs.