Introducing the Bacco Network Upgrade

tl;dr

After several months of intense development from core development teams, including Proxima Labs and Wonderland, we’re excited to announce the latest Connext network upgrade, Bacco.

• Bacco upgrades the existing “slow path” of the Connext Network to operate optimistically, reducing the operational costs of supporting new chains by over 90% while maintaining the best possible security.
• Bacco opens the door to rapidly expanding Connext to many new chains & L2s! 🎉
• In line with this, the Connext Foundation has put forward a DAO RFC to approve future protocol support for 20 new chains & L2s.*

The Bacco network upgrade is set to occur on December 14th, pending successful production testnet monitoring.

Why Do We Need Bacco?

Today, Connext’s messaging layer utilizes the underlying “canonical” messaging bridges that connect L2s to Ethereum (e.g., rollup bridges such as the Arbitrum AMB). When a message passes through Connext, roots must travel from the L2 chains we connect (known as spoke domains) back to Ethereum L1 (the hub domain) through the canonical bridges. Once there, roots are aggregated into a single Merkle root that is propagated to each spoke domain. We often refer to this as the “slow path”.

While this construction allows Connext to maintain the best possible security, inheriting it from the chains themselves, it makes adding new spoke domains prohibitively costly (~$30k/mo/chain at a 20 gwei gas price 😱). Rollup/canonical bridges are very expensive at scale.

As ecosystems continue to deploy new chains (Op Superchain, Arbitrum’s Orbit, etc.) and creating rollups becomes easier (Gelato’s RAAS, AltLayer, etc.), builders and users alike will need secure crosschain infrastructure that can expand with them.

An Optimistic Solution

The Bacco network upgrade changes how messages are passed between chains to behave optimistically — messages are transported between chains by the Connext Sequencer (subject to a fault proof window and disputes by Watchers) instead of through the sequencers of other rollups. This results in a massive improvement in operational efficiency, reducing the overhead cost of adding a new chain by over 90% while maintaining the best possible security.

Optimistic Path

Here’s how it works:

1: Aggregating Roots on Ethereum: Periodically, the Connext Sequencer takes a snapshot of all new crosschain transactions from the spoke domains and submits an aggregate root directly to Ethereum.

2: Fraud Detection and Prevention: Once submitted, the system initiates a 30-minute fault detection window, during which the Watchers check to ensure the aggregated root only contains valid transactions from the spoke domains.

• Once the integrity of the aggregated root is verified and the 30-minute window elapses, the Sequencer will submit the same aggregated root to all spoke domains, where the fault detection process is repeated once more before the transaction is executed.

3: Slow Path Fallback: On the off chance the Sequencer submits an aggregate root with a bad transaction, any Watcher can trigger a fault proof. The system then falls back to the original slow mode described above, pushing all data directly through canonical bridges. In the future, the system would also subsequently penalize either the Sequencer for a fault, or the Watcher for an invalid fault proof based on the (ultimately correct) state passed through canonical bridges.

• As an additional guardrail, until staking and slashing are implemented, the system would remain in slow mode after a fault proof until the Connext DAO or Security Council voted to reenable the default optimistic mechanism.

This approach maintains Connext’s commitment to the best possible security while significantly reducing the gas costs on Ethereum of operating the network.

💡 Fun Fact: The above system upgrade quite literally makes Connext an application-specific Optimistic Rollup.

For Optimism and Arbitrum, the rollup is defined by an EVM-compatible state machine that lives in the “dispute path” on Ethereum. For Connext, the rollup is defined by a much simpler state machine: the L1 bridge contracts of other rollups and chains posting to Ethereum.

Intents & Fast Execution

It is important to note that Bacco only changes the way that lower-level settlement occurs within the protocol. Connext’s intent layer, which sits on top of the messaging system described above (and is operated by Connext Routers) works exactly the same way in both cases, allowing users and protocols to quickly transfer tokens between chains near-instantaneously.

When users transfer tokens or call contracts across chains, Routers immediately execute the transaction at the target chain using their own funds. Then, they wait for the messaging layer system to repay them.

Upgrade Details

The Bacco network upgrade will be a rolling upgrade, requiring no action or changes from users, applications, or routers.

• There will be no downtime for fast-path transactions in the network.
• Applications & routers should expect some delays in slow-path transactions while the upgrade is occurring.
• The mainnet upgrade is scheduled for the 14th of December, pending some final testnet monitoring.
• The upgrade was approved by the Connext DAO as part of a formal vote that concluded yesterday, the 6th of December.
• You can read more about the upgrade, its specification, and design rationale in the original DAO RFC post here.

What Bacco Means for the Connext Ecosystem

The Bacco upgrade marks the start of Connext v2’s rapid expansion to new chains. Connext has begun this process already with:

• The launch of Linea support last week
• Kickoff of voting to add support for Base this week
• Today, an RFC was submitted to the Connext DAO to seek approval to add future protocol support for 20 new chains. This proposal is intended to streamline the process of adding additional chains, allowing Connext to adapt to the growing needs of the ecosystem.

Want to get involved?

We’d love for you to get involved in the Connext DAO and help shape the future of Connext. If you haven’t already, check out forum.connext.network for the latest on the DAO governance, and join the Connext Discord to learn more about integrating Connext.

*This proposal is not an all-encompassing list of chains that Connext may support, nor a commitment to support each of the chains included in the proposal. We anticipate the introduction of similar proposals throughout the year to request approval for additional chains.

About Connext

Connext is a network for fast, trustless communication between chains and rollups. It is the only interoperability system of its type that does this cheaply and quickly without introducing any new trust assumptions. Connext is aimed at developers who are looking to build bridges and other natively cross-chain applications. To date, over $1.5b in transactions have crossed the network.