According to Coincu, L2Beat's latest documentation emphasizes the distinction between Validiums, Optimiums, and traditional Layer 2 (L2) solutions. Validiums and Optimiums, which include Immutable X and Arbitrum Nova respectively, do not publish data on Layer 1 (L1), introducing additional trust assumptions. As a result, if the operator of an off-chain decentralized application (DA) solution fails to provide the necessary data for reconstructing the state, funds are put at risk.
Although they are not classified as L2s, Validiums and Optimiums are included in L2Beat's documentation for historical reasons and to provide a comprehensive overview of the space. In terms of trust-minimized L2s, L2Beat recognizes several categories, including zkRollups, Optimistic Rollups, State Channels, and Plasma. zkRollups and Optimistic Rollups both publish data on L1 and rely on validity proofs and fraud proofs for state roots correctness, respectively. State channels and Plasma do not publish data on-chain, with the former requiring users to retain their data for proper exiting and the latter utilizing fraud proofs for dispute resolution. However, Plasma does not support general computation.
