What is a Validium?
A validium is a Layer 2 scaling solution that uses validity proofs (like ZK rollups) for execution correctness but stores transaction data off-chain rather than on Ethereum. This hybrid approach offers much lower costs than full ZK rollups while maintaining computational integrity guarantees, but introduces different security assumptions regarding data availability.
How Validiums Work
Validiums process transactions off-chain and generate validity proofs demonstrating correct execution. Exactly like ZK rollups. These proofs are verified on Ethereum, ensuring computational correctness. However, the underlying transaction data is stored with off-chain data availability committees (DACs) or external DA providers rather than published to Ethereum.
The smart contract on Ethereum tracks state roots and verifies proofs, but cannot independently reconstruct the validium's state from on-chain data alone. Users must trust that data availability providers will supply data when needed for exits or state verification.
Security Model
Validium security guarantees differ from rollups in important ways. Computational integrity is fully maintained. Invalid state transitions are rejected just like in ZK rollups. Proofs cannot be faked or falsified. However, if data availability providers collude, fail, or are censored, users may be unable to prove their balances for exit.
The tradeoff is explicit: funds cannot be stolen through invalid computation, but might become inaccessible if DA fails. Users must evaluate whether the data availability committee is trustworthy, sufficiently distributed, and legally/technically resilient.
Cost Advantages
By avoiding on-chain data posting, validiums achieve dramatically lower costs than rollups. Transaction fees can be 10-100x cheaper than ZK rollups posting data as blobs. For applications where the DA tradeoff is acceptable. High-volume, lower-value transactions, gaming, or situations with trusted operators. Validiums offer compelling economics.
StarkEx powers several validium deployments including dYdX (v3), Sorare, and Immutable X. These applications prioritize throughput and cost for trading, gaming, and NFT use cases.
Volition: User Choice
Some systems offer "volition". User choice between rollup mode (on-chain data, higher cost, maximum security) and validium mode (off-chain data, lower cost, different trust assumptions) per transaction. This enables optimal tradeoff matching for different use cases within a single system.