Optimism's unveiling of a fault-resistant system has now reached OP Sepolia. These measures ensure the security of valid transactions on rollups, serving as the final testing ground before deployment on the mainnet.

Previously regarded as fraud proofs primarily used to validate transaction legitimacy, optimistic rollups like Optimism and Arbitrum process transactions off-chain before posting data back on Ethereum as "calldata." Over the past two years, their usage has surged, handling more transactions than the mainnet Ethereum.

Optimistic rollups aim to tackle the blockchain trilemma by providing a layer 1 network design that balances scalability, security, and decentralization. They introduce a time window accessible to everyone to verify transaction states, enhancing network security and combating fraudulent activities.

Despite Optimism's current lack of a fault-proof system, it relies on a seven-day window challenge during system upgrades to identify any fraudulent activity. In October 2023, Optimism introduced its fault-proof system, comprising a fault-proof program (FPP), a dispute game protocol, and a fault-proof virtual machine (FPVM) on the OP Goerli testnet. The latest testnet iteration, launched on OP Sepolia, features permissionless validation, allowing anonymous participation and facilitating ERC-20 and ETH token withdrawals without the involvement of a trusted third party.

According to OP Labs CEO Karl Floersch, the ultimate goal is to accelerate decentralization through fault-proof systems, transitioning information between layers 1 and 2. The open-source nature of OP's fault-proof system, coupled with a bug bounty program, promises a secure future in the crypto ecosystem.