Written by editor James Bourne 

Stop us if you've heard this one before: for blockchain technologies in 2025, one of the biggest themes will be around interoperability. Yet this coming year may see significant innovation and progress around one of the space's thorniest problems.

The nirvana of a fully interoperable blockchain, working seamlessly and collaboratively across platforms and applications, opens almost limitless doors. Indeed, it is the mission statement for Web3. At its core, as Ethereum, whose co-founder Gavin Wood coined the term, defines it, it is decentralized, permissionless and trustless, with ' for blockchain advocates ' a native payment system, cryptocurrency, underpinning it.

Another widely-held theory for Web3 is regarding the convergence of technologies. These can vary depending on who you read ' Internet of Things (IoT), AI and blockchain is a common one ' but blockchain and AI are often the bulwarks. Why? As an article from the World Economic Forum outlines ' swapping IoT for spatial computing ' the shared data infrastructure of blockchain provides the foundations on which to build, while generative AI provides the velocity of rapid design and deployment of digital environments.

Whereas the pace and promise of generative AI continues to accelerate, the potential of an interoperable blockchain feels stuck at the starting gate in comparison. According to Electric Capital's 2023 Crypto Developer Report, one in six developers write code on three or more blockchains. Blockchain interoperability increasingly feels like the missing piece of the puzzle for true Web3.

The current ecosystem

Blockchain architecture consists of several layers. Layer 0 represents the physical foundation upon which the blockchain is built. Layer 1 (L1), including Bitcoin, Ethereum and Binance Smart Chain, is the base layer and stores an immutable transaction log, though in the first instances it was extremely limited in terms of interacting with other blockchain networks.

Layer 2 (L2), such as the Ethereum-based Polygon and the Bitcoin-based Lightning Network, is an overlapping network, including third-party integrations to increase system throughput. Layer 3, the application layer, is primarily centred around Ethereum and represents a greater ability for customisation and scalability.

Currently, there are various approaches and protocols to bring about greater interoperability, each of which are proclaimed as the saviour. Blockchain bridges, or cross-chain bridges, are aimed at connecting two blockchain ecosystems. The Binance Bridge, for example, enables users to transfer assets between the Binance Chain and chains such as Ethereum. There are notable security risks, however; the Wormhole bridge, which connects Solana and Ethereum, had its security compromised in 2022 at a cost of $320 million.

The Cross-Chain Interoperability Protocol (CCIP), developed by Chainlink as far back as 2021, aims to establish universality, as a 'generalised cross-chain messaging protocol for transferring tokens (value), messages (data), or both tokens and messages simultaneously within a single cross-chain transaction.' Another protocol going further back, the Cosmos-developed Inter-Blockchain Communication Protocol (IBC) in 2019, allows heterogeneous chains to trustlessly communicate with each other to exchange data, messages and tokens. Cosmos describes this as the 'Internet of Blockchains' and now boasts more than 115 chains.

Atomic Swaps, meanwhile, allow the exchange of cryptocurrency across different blockchain networks without intermediaries through Hash Time-Locked Contracts (HTLCs), which as the name suggests require a correct passphrase within a set timeframe.

Contenders for 2025

There are a few irons currently in the fire for the future of interoperability. One emerging approach is through restaking, where staked cryptocurrency can be redeployed to create a platform with shared security. This theoretically provides a sweet spot between scalability and security, as the Ethereum-based EigenLayer, a leader in restaking, proves; enabling Ethereum validators to 'maximize the utility of their staked ETH while providing robust security guarantees for new protocols.'

There are concerns ' overextending across too many chains could lead to security vulnerabilities, for instance ' but as Altan Tutar put it in December, restaking can 'provide a gateway to true interoperability.' 'Assets can now have mobility across different chains and the ability to contribute to multiple chains, leading to one ecosystem of infinite chains,' Tutar wrote.

Of the many startups in this space, Symbiotic, which went live on Ethereum mainnet in January, stands out. Its approach is through a neutral coordination framework. 'Rather than forcing protocols to build security systems from scratch or conform to rigid designs, Symbiotic provides flexible primitives that enable customizable security configurations while maintaining full control,' the company wrote.

Regarding other launches, Polygon announced the launch of the 'pessimistic proof' for AggLayer, a cross-chain settlement layer which aims to 'fix' the fragmentation across thousands of L1 and L2 chains by leveraging zero-knowledge (ZK) proofs, in May.

'The pessimistic proof provides the cryptographic guarantee that allows chains to connect to a shared bridge without additional trust assumptions,' the company explained. 'It ensures that, even if a chain's security is compromised, it cannot drain funds from other chains.

'A pessimistic proof does this by constantly ensuring that no chains are lying about deposits to their chain.'

Axelar, a Canada-based startup, has thrown its hat into the ring with the launch of its Mobius Development Stack (MDS) in November. The MDS 'enables customizable, self-service connection with any blockchain or off-chain system, integrating communities, compute sources, security mechanisms and liquidity pools into a secure, unified user experience' in the company's own words. Zeus Network, meanwhile, focuses on bridging Bitcoin and Solana, with a mission to scale Solana with cross-chain liquidity permissionlessly.

Perhaps the overall result will be something in between. 'The future of blockchain interoperability will likely involve hybrid approaches,' a blog from blockchain and smart contract software provider Bitium noted. 'As the technology matures, we can expect more sophisticated solutions that combine the strengths of different interoperability mechanisms.'

Find out more about topics like this at Tokenize:LDN, happening in London on 2 - 3 December.