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BRC-721: The Token Standard Defying Bitcoin’s 4MB Storage Limit

BY Langston Thomas

June 13, 2023

On February 1, developer, crypto advocate, and Taproot Wizards founder Udi Wertheimer made history by purposefully orchestrating the largest block and transaction in Bitcoin’s history. In minting the first of many wizards to come, he achieved the absolute maximum BTC block size of 4MB, something that many, up until this point, thought was impossible.

Just a few months later, on May 22, members of the Spirit DAO — a coalition of collectors devoted to elevating the Azuki universe — effectively blew Wertheimer’s record out of the water. By minting a 6.9MB Comic Banner on Bitcoin, the DAO stole the crown, solidifying the piece as the largest file size stored on BTC to date.

But how? Considering that the max block size on Bitcoin can’t exceed 4MB, what sort of wizardry did the Spirit DAO implement in their feat? Well, it all has to do with BRC-721, a new type of NFT token standard revolutionizing something called “Smart Inscriptions” on Bitcoin.

What is BRC-721?

Degens will immediately recognize BRC-721’s acronymous name as being akin to ERC-721 — AKA the premiere token standard for Ethereum NFTs. Put simply, BRC-721s are smart-contract-based NFTs, but on BTC.

But there’s more to it than that, of course. BRC-721 was inspired by the experimental BRC-20 token standard created and launched in March 2023 by an anonymous developer Domo. BRC-20 was created to give Bitcoin a more sophisticated NFT functionality, but it was centered around fungibility and lacked one thing: smart contracts.

In place of smart contracts doing the heavy lifting for NFT creators (as they’ve for years now on Ethereum), BRC-20 lets users store a script file on Bitcoin, using Ordinals to write JSON data to Satoshi (sats) — the atomic unit of Bitcoin. In lieu of getting into the thick of that functionality here, you can read more in our full explainer on Ordinals.

What’s important to know is that BRC-721 builds upon the principles of BRC-20 but aims to extend the capabilities of Bitcoin tokenization to include true non-fungible tokens. To do so, BRC-721 brings the tried and true smart contract functionality that the NFT space knows and loves from Ethereum over to Bitcoin. And it’s all made possible by the Trustless Computer protocol.

So, in contrast with Ordinals Inscriptions, where metadata is attached to information that is inscribed directly to the Bitcoin blockchain (essentially as text files), the BRC-721 protocol functions as a solidity smart contract running on Bitcoin. This means that while metadata is still minted on-chain, BRC-721 operability transcends that of Ordinals by offering programmability (Smart Inscriptions), larger storage limits, and reduced network fees.

Who’s using BRC-721?

There are three major names to know when it comes to understanding the current state of BRC-721. They are New Bitcoin City (NBC), Smart Inscriptions, and Trustless NFTs. Essentially, everything comes back to NBC. Billed as a “radically new way to explore Bitcoin beyond just a currency,” the platform is built on the Trustless Computer protocol and acts as a “diverse corner of Web3” where crypto-art, DeFi, AI, and more facets of the metaverse converge.

NBC also plays a pinnacle role in the BRC-721 ecosystem. On March 29, the platform broke ground with the release of Sudos, a collection of 1,024 fully on-chain penguin-themed collectibles that effectively became the first BRC-721 venture to ever exist.

That brings us to Smart Inscriptions, the term coined by NBC to exist in place of “BRC-721.” Essentially Smart Inscriptions are to BRC-721 as NFTs are to ERC-721. That is to say that they’re a shorthand version, parallel to Ordinals Inscriptions, to define the growing categories of NFTs on BTC.

Of course, tokens that can’t be traded are essentially just a consolation prize of the blockchain. So to give greater utility to the BRC-721 ecosystem which it created, NBC unveiled Trustless NFTs on June 9, a marketplace for Smart Inscriptions. To date, over 1,000 Smart Inscriptions have been created and added to the Trustless NFTs platform, including Sudos, Fading Memories, GlixPunks, and more, that served as the first public BRC-721 collection launches.

Is BRC-721 catching on?

Similar to the numerous other types of new Ethereum and Bitcoin-based tokens that have been cropping up as of late, only time will tell how significant of a facet BRC-721 might turn out to be. Given the sustained popularity of Ordinals, though, Smart Inscriptions could easily become yet another market mover to look out for.

Yet, it’s not only thanks to the hype cycle that BRC-721 is starting to be talked about. Rather, the unlimited storage limit and fee reduction should both be major points of interest for any and all creators and traders in the Bitcoin NFT ecosystem. And considering the Spirit DAO has already staked its claim, surely more builders will follow suit.

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