What blockchains does 0x API support?

Swap API is available on Ethereum (Mainnet and Goerli) as well as various EVM chains and L2 solutions, including: Arbitrum, Avalanche, Celo, Binance Smart Chain, Fantom, Optimism and Polygon (Mainnet and Mumbai). Tx Relay API is currently available on Ethereum and Polygon, with support for more EVM chains coming soon. Orderbook API is available on Ethereum, Binance Smart Chain and Polygon.