# V3 or V4 - Which version should I use? Currently there are two versions of the NFT Swap SDK: [0x v3](https://github.com/0xProject/0x-protocol-specification/blob/master/v3/v3-specification.md) and [0x v4](https://protocol.0x.org/en/latest/). ### Which version? tl;dr: By default, **we recommend using V4.** It's the future of the 0x protocol and is hyper gas-optimized (currently the cheapest way to buy/sell NFTs on Ethereum). **One exception:** V4 currently does not support buying and selling bundles. If you require bundle support in the short term, you will need to use V3. Eventually V4 plans to be able to support bundles, but for now use V3. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.swapsdk.xyz/v3-or-v4-which-version-should-i-use.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.