# The median-4% invariant: a manipulation-robust price without an oracle

> Canonical: https://blazephoenix.xyz/learn/median-4-percent-invariant
> License: CC BY 4.0 (attribution + link) · © 2026 BlazePhoenix
> Updated: 2026-08-05



BlazePhoenix V2 is pre-deployment and under audit; this describes the designed mechanism. A single spot price is trivial to poison: move one thin pool and the number moves. The classic fix is an external oracle, which reintroduces a trusted third party. V2 instead takes a median across independent on-chain sources and accepts a value only if it sits within a bounded robustness band.

## Why the median, and why 4%

The median is the order statistic that a minority of manipulated inputs cannot drag: to move a median you must corrupt half the sample, not one member of it. The 4% band is the tolerance the design allows between the accepted price and the cluster of honest sources; a source outside the band is treated as an outlier, not as truth. The effect is oracle-grade robustness computed entirely on chain, with no feed to trust or bribe.

**Verify it yourself:** Reproduce the idea off-chain: take five pool prices for a pair, poison one by 50%, and confirm the median barely moves while the mean does

Related: https://blazephoenix.xyz/learn/stochastic-invariants · https://blazephoenix.xyz/learn/oracle-free-lending · https://blazephoenix.xyz/learn/phantom-liquidity · https://blazephoenix.xyz/learn/v2-redesign-overview