In his blog post, Endgame, Vitalik lays out his vision for scaling Ethereum. Ethereum block space is limited & expensive – there is simply not enough compute to run everything on Ethereum. If this problem is to be solved without compromising security, he suggests three components are required: a decentralized settlement layer, low-cost rollups, and an optimistic interchain communication network. Two years later, Ethereum has become that settlement layer, and low-cost optimistic rollups are plentiful.
Yet one piece of the puzzle remains unsolved: the optimistic interchain communication network.
Today, we are launching testnets of the Synapse Interchain Network (SIN) and Synapse Chain. This is the full stack required to achieve the endgame, the last remaining puzzle piece in Vitalik’s vision.
Synapse Interchain Network (SIN) — The first optimistic proof-of-stake interchain network, enabling trustless communication and settlement between chains.
Synapse Chain — An optimistic rollup that serves as data availability for the Interchain Network, where network agents stake tokens, confirm transactions and submit fraud proofs. With the Interchain Network natively enshrined, apps on Synapse Chain have access to all interchain state to execute interchain transactions seamlessly.
SIN is the first optimistic proof-of-stake interchain network, enabling trustless communication and settlement between chains. Apps built on SIN have all blockchain data accessible, and liquidity transferable across all chains.
With SIN, transactions across chains now have the same reliability as that you do in transactions on a single chain. SIN is built like an L2 and is secured like an L2, but it expands upon what L2s make possible. This expansion of the principles behind Ethereum and rollups will unlock an entirely new set of crypto primitives.
All SIN transactions are optimistically verified, and the full interchain state can be recreated from Ethereum. Following these principles, the network is trustless, permissionless, and modular:
Trustless — A single honest actor maintains network security, as long as there is at least one honest agent, fraudulent messages aren't executed. The network doesn’t rely on centralized oracles or permissioned relayers to validate transactions.
Permissionless — Anyone can run an agent, strengthening network security & competing for fees. Furthermore, agents can permissionlessly support new chains.
Modular Security — Different types of use cases have different security needs. SIN’s security architecture supports them all. Apps can leverage the customizable optimistic period to ensure interchain integrity. This flexible design enables the full range of interchain use cases, from multi-billion dollar Dapp governance to NFT bridging.
Solving the interchain communication problem is important enough to require its own network with its own economics. Just as L1 gas fees represent the cost of on-chain compute, SIN transaction fees represent the cost of interchain compute.
Agents stake to start confirming SIN transactions
Fees are paid for every transaction sent on SIN
Fees are split among honest agents involved in confirming transactions
Dishonest agents have their stakes slashed and given to honest agents
ETH’s ecosystem built around gas fees allowed LSDs (liquid staking derivatives) and DPOS (delegated proof of stake) to flourish. SIN fees create the opportunity for an ecosystem built around interchain compute fees. As trustless interchain compute becomes a reality, Interchain compute will become as valuable as on-chain compute.
In the future, network stakeholders may vote on what token agents use for staking and how to allocate SIN fees.
SIN uses Synapse Chain as its coordination hub.
Message attestations, agent stakes, and fraud reports are all posted there. This allows SIN to get the benefits of Synapse Chain’s cheap & near-instant transaction confirmation, while maintaining Ethereum as the data availability layer of last resort.
All SIN transactions get posted to Synapse Chain, which as an Ethereum L2, posts all transactions to Ethereum. The full SIN interchain state can always be recreated from Ethereum.
An Ethereum-based optimistic rollup built on the Syn OP stack. With the Synapse Interchain Network natively enshrined, apps built on Synapse Chain have access to all interchain state and the ability to execute interchain transactions seamlessly. Transactions on Synapse Chain are near instant and cost a fraction of what they would on Ethereum. As an Ethereum-based rollup, Synapse chain takes advantage of the decentralization and security of Ethereum. All transactions on Synapse Chain are posted to Ethereum allowing full reconstruction of the chain from Ethereum.
Modularized L2 Bridge: Synapse Chain allows for interchain deposits from any Synapse Interchain Network supported chain as well as fast withdrawals from the standard L2 bridge contract.
Interchain Data Availability Layer: Synapse Chain serves as the interchain data availability layer for the Synapse Interchain Network. All SIN agents stake on Synapse Chain making all state from all other chains natively available. Contracts deployed to Synapse Chain are immediately networked to all supported chains, allowing them to read state from any other chain and execute interchain transactions.
Ethereum-based rollup: As an Optimistic Rollup, Synapse Chain writes all transaction data to Ethereum. Being an EVM chain also allows developers to tap into Ethereum’s vibrant developer ecosystems & use their favorite packages and tools.
On the Sepolia-based Synapse Chain testnet, gas fees for transactions are paid in Sepolia ETH. All Synapse Interchain Network agents stake on Synapse Chain and pay gas fees on Synapse Chain as they validate transactions. The more interchain transactions and dApps are built on top of SIN the more transactions are processed on Synapse Chain.
In the future, other tokens could be used for gas on Synapse Chain.
Synapse Interchain Network contracts are open source and audited by Zellic & Trail of Bits, audits will be published in coming weeks.
Synapse Labs is excited to work with the Synapse DAO to enable the interchain future. This proposed path represents some of the most in-depth work & research into interchain communications.