Ethereum (ETH)’s fees are hard-coded to only be payable in Ether, but a clever trick with smart contracts allows users to effectively pay for gas with a special token, which reduces the total fee they incur.
This principle was used by the team behind 1inch.exchange, a decentralized exchange aggregator, to introduce the Chi token. The technology was formally announced on June 5, and it builds on a previous iteration of the concept, called Gas Token (GST).