0x API /swap now supports 0x Protocol v4

TL;DR

• v4 is the most powerful upgrade of the 0x Protocol, making it the most gas-efficient DEX protocol (up to 70% gas savings with RFQ liquidity).
• Users can expect more competitive liquidity from professional market makers and in turn better prices through 0x API.
• The default allowanceTarget returned by /swap/v1 has changed to 0xdef1c0ded9bec7f1a1670819833240f027b25eff. This allows us to lower costs for your end users by a measurable amount. The old allowance will be deprecated on March 31st.
• If you are a developer building with 0x API and consuming RFQ liquidity via /swap/v1, we encourage you to update the takerAddress to be a non-contract EOA address to ensure your continued access to RFQ liquidity.
• We will stop supporting /swap/v0 on March 31st.

The 0x API is designed to make it easy for DeFi developers like you to tap into both off-chain and on-chain DEX liquidity in a fast, reliable, and easy to use way so you can focus on what matters: your product. As of February 12th, 2020, the /swap/v1 endpoint supports 0x Protocol v4.

This version of the 0x Protocol is the most powerful update made to the protocol to date, turning it into the most gas-efficient DEX. As a result, users of applications built with 0x API can expect more gas efficient orders (up to 70% gas saved for RFQ orders and 10% for limit orders) and even better prices from 0x professional market makers.

If you are building with 0x API /swap/v1 , here’s what you need to know:

New allowanceTarget

The default allowanceTarget returned by /swap/v1 has changed to 0xdef1c0ded9bec7f1a1670819833240f027b25eff. This allows us to lower costs for your end users by a measurable amount:

However, we understand if you don’t want to migrate your users just yet. This is a soft change and the old allowance (0xf740b67da229f2f10bcbd38a7979992fcc71b8eb) will continue working until March 31st — when we deprecate it.

Upgrade takerAddress

With the update to 0x Protocol v4, RFQ orders no longer have a protocol fee and require a tx.origin to be specified. This allows 0x market makers to price for the user, rather than the entire integration.

If you are using /swap/v1, note that it now requires takerAddress to be the end user submitting the transaction (i.e. an EOA). Depending on your integration, you might be setting takerAddress to a contract address you were filling from. The expected experience is that when takerAddress is a contract no RFQ orders are served, so we highly encourage you to update takerAddress to be a non-contract EOA address to ensure your continued access to RFQ liquidity.

Deprecation of /swap v0

We will stop supporting /swap/v0 on March 31st. If you are currently using the older version of /swap we highly encourage you to move over as soon as possible. v1 has a lot of benefits over v0, including:

• Aggregation of 0x API exclusive liquidity sources, 0x RFQT and 0x private AMM, which translates into better pricing.
• Lower gas usage due to our super optimized contract that allows 0x API to source Uniswap and Sushiswap liquidity in a more gas efficient way than the default Uniswap and Sushiswap contracts.
• The 0x protocol fee is no longer incurred for RFQ and external liquidity sources, lowering transaction costs further.

You can learn more about these and other benefits here. If you are ready to move over to v1, we put together this guide to help you in the process.