#dYdX is a decentralized exchange (DEX) built for derivatives trading, especially perpetual contracts (derivative trades with no expiry date). 
It evolved over time. Earlier versions ran on Ethereum (or Ethereum + Rollups) and used off-chain order books + on-chain settlement. 
In its more recent architecture (“v4”), dYdX now runs on its own Layer-1 blockchain, built with the Cosmos SDK / CometBFT consensus (a PoS / Delegated PoS system) to optimize for derivatives trading. 
The shift to this native chain gives it more control over fees, performance, and governance.