Security in XChain is per-asset, not per-chain. Every asset carries a minimum security-class, and a high-value asset simply cannot exist on the Data Layer. This makes "downgrade" attacks structurally impossible, and rests the safety of value on cryptography and capital rather than on trusting a small validator set.

For high value (T0–T1), three layers combine:

ZK validity proof — even a fully-compromised committee cannot forge invalid state; it loses liveness, not safety.
Global restaking — fraud on any chain slashes global capital.
Watcher / fraud proof — detection and challenge.

Low-value data (T3–T4) is secured by proof-of-publication only. Three chain security-classes span the range: SOVEREIGN (own validators, T3–T4) → SHARED (Partial Set Security, T1–T2) → ZK_SECURED (proof mandatory, T0–T1). Pessimistic proofs provide failure isolation: a faulty chain can lose only its own share.

Takeaway: binding a security-class to each asset is the keystone — it turns "don't put value in the wrong place" from a guideline into a structural guarantee.