Initially, I wasn't surprised to hear that @NervosNetwork was making a desperate bid for BTC layer2. This is because CKB's public chain technology is close to BTC yet ahead of BTC; it can inherit the native UTXO characteristics while achieving more advanced programmable feature extensions. If it is almost impossible for the CKB public chain to surpass the narrative of BTC, then as a second-best option, its BTC layer2 will definitely be an invincible existence. Why? Next, let's talk about my views on CKB.
The current BTC layer2 market is limited by the verification capabilities of the BTC mainnet, resulting in a blossoming situation. Indeed, it is precisely because the BTC mainnet's scripting language is inherently simple, coupled with its computing and verification capabilities approaching zero, that it provides ample space and opportunity for market development. Currently, apart from limited transaction verification and multi-signature within UTXO unlocking conditions, everything else requiring verification data, state changes, and other complex transaction logic cannot be directly realized, and BTC can only serve as an asset settlement layer while extending a powerful public chain to build local consensus and computable verification capabilities for expansion. This makes the landing standards of BTC layer2 not standardized, there is no concept of 'orthodoxy', and it is even hard to distinguish between high and low. The distinction can only be made according to the community's perception, dividing it into narrow and broad senses: in a narrow sense, only the Lightning Network state channels and RGB's single seal extension plans ensured by a single seal are truly the orthodox BTC layer2, as they fully utilize and leverage BTC's limited script verification capabilities, requiring minimal or no reliance on off-chain local consensus. In a broad sense, as long as the local consensus of the extension chain is recognized and there is a cross-chain bridge solution ensuring the safe migration of assets, theoretically, Ethereum EVM chains, Solana high concurrency performance chains, and so on can all act as BTC layer2. Clearly, the current BTC layer2 market is obviously polarized, either extremely narrow, like the Lightning Network and RGB, developing slowly and facing many obstacles, or extremely broad, where any performance chain that can achieve secure asset interaction with the BTC mainnet can be called BTC layer2. So, is there a 'compromise' solution? Yes, the answer is: the underlying technology framework that uses the UTXO model and has adapted and upgraded its performance @NervosNetwork. The specifics are as follows:
1) CKB Network and BTC share the same lineage in 'UTXO model, mining consensus mechanism', which is different from the account balance model of mainstream public chains like Ethereum. UTXO has certain unique advantages in transaction privacy, flexible transaction construction, and parallel processing to prevent double spending, making it one of Satoshi Nakamoto's greatest inventions. This also explains why after Ethereum, Sui and Aptos adopted a similar UTXO model. We can say that Bitcoin's capacity and block speed have limitations of the era, but the UTXO model is quite advanced. CKB inherits the UTXO model and optimizes and upgrades it to the Cell model, which retains the purity of Bitcoin's UTXO model while providing the data state of account models like Ethereum. To put it simply: the creation and destruction of Bitcoin's UTXO model are similar to coins being continuously destroyed and minted, while Cells eliminate the destruction process, aiming to validate and permanently preserve state. Each Cell contains Capacity and Data fields, where Capacity in bytes corresponds to the UTXO balance; Data stores all historical transaction states and other arbitrary forms of data. This allows the collection of Cells not only to accurately express balance and handle asset transfers but also to encompass a series of complex states of smart contracts. Overall, the Cell model is a leading trading model with stronger sustainability, better flexibility, and can expand the applicable range of the UTXO model. It is also the key for CKB to inherit the security of the BTC mainnet while 'accelerating' the slow expansion directions of Bitcoin, such as Lightning Network and RGB.
Taking the recent CKB launch of RGB++ as an example, under normal circumstances, the difficulty in developing a mature RGB solution in the BTC ecosystem is not the one-time sealing process of the BTC mainnet, but rather the communication, coordination, and joint maintenance of state between off-chain client verification nodes, especially in a decentralized and dispersed node environment. In other words, RGB may seem easy in theory, but its practical implementation is heavily obstructed by limitations such as foundational infrastructure.
CKB sees this clearly and lets all these nodes doing off-chain client verification participate in the public verification process on the CKB chain. This directly accelerates the UTXO extension client practical path that RGB wants to achieve. After all, achieving complex P2P node network consensus in an off-chain client environment is very challenging, filled with complexities and challenges, such as the off-chain communication possibly facing data synchronization delays or inconsistencies, as well as some fraud and attack challenges. If this process can be transferred to the on-chain environment, it would actually be simpler. RGB++ has recently been discussed a lot, and I will add a CKB proposed Open Transaction data format, which will allow everyone to feel the advanced features of the CKB chain. In simple terms: Open Transaction allows multiple participants to build and aggregate different transactions over different times, including partial construction, allowing modifications, incremental construction, and aggregation. For example: Alice creates an Open Transaction, stating she wants to exchange a certain amount of token A from Bob for token B, and this transaction remains editable after being initiated. If Bob agrees to the transaction conditions upon receiving it, he can add his token B and supplement the transaction conditions. At first glance, this may seem abstract; for instance, in a cross-chain scenario, Alice and Bob can autonomously complete asset transactions on different heterogeneous chains, greatly enhancing the cross-chain operability of the CKB chain; in complex DeFi transaction scenarios, the DeFi that users participate in may need to be dynamically adjusted according to market changes. Through Open Transaction, contract participants can flexibly adjust transaction conditions during the execution of the contract, which undoubtedly greatly enriches the complexity handling capability of transactions.
In my opinion, Open Transaction and UTXO transaction unlocking conditions are similar, able to integrate complex transaction unlocking conditions, multi-signature participation, and complex application scenarios into one, and this is also a value innovation derived from the BTC main chain idea. Interestingly, the first work of @busyforking, a member of the Ethereum core development team, actually adopted BTC's UTXO model. Although Ethereum's smart contract model is now more widely applied, Jan and his Nervos team stubbornly chose to extend and upgrade on top of BTC's UTXO model. This expresses a reverence for Satoshi Nakamoto's minimalist UTXO transaction model and, in a sense, plants the seeds for it to become a BTC Native layer2.
To summarize: I am very optimistic about CKB doing BTC layer2. In the short term, it can indeed speed up the implementation of Lightning Network and RGB on UTXO model chains, at least providing meaningful references for the expectations of these two orthodox expansion plans on the BTC mainnet; in the long term, the chain's native features and underlying architectural compatibility of CKB can help it go further in this chaotic battle of BTC layer2 without standards.
