Glossary
Validium
A Layer-2 design that posts validity (ZK) proofs to L1 but keeps transaction data off-chain — dramatically cheaper than rollups, at the cost of a separate DA assumption.
A validium combines ZK validity proofs with off-chain data availability. Like a ZK rollup, every state transition is cryptographically proven correct on L1. Unlike a rollup, the data behind those transitions is not posted to L1 — it lives on a separate data-availability layer (a DAC, Celestia, EigenDA) or in a permissioned data-availability committee.
The trade-off is materially cheaper transactions in exchange for a weaker data-availability assumption: if the off-chain data becomes unavailable, withdrawals from the L2 may stall. StarkEx deployments (dYdX v3, Immutable X) ran as validiums; Polygon zkEVM offers a validium mode.