Leios monthly spotlight: September highlights

Summary:

• Leios has transitioned from Input | Output Research to Input | Output Engineering
• Clarifications and cost analyses are underway following constructive feedback for CIP-0164
• A simulator bug was identified and fixed, leading to improved results
• Impact analysis suggests minimal disruption to most Cardano ecosystem systems from the proposed design
• Blink Labs (Go) made progress on certificate types, initial block shapes, transaction hashing, and a notify mini-protocol
• Next steps include supporting specifications, conformance guidance, iterative prototypes, public roadmap visibility, and continued editor engagement
• The community is invited to an open review and demo call on October 29.

As part of Input | Output (IO)’s ongoing commitment to advancing Cardano’s scalability and transparency, the Ouroboros Leios project continues to make steady progress toward realizing the next major leap in performance. Developed to address throughput and efficiency without compromising security or decentralization, Leios is now moving from research to active engineering as part of Input Output | Engineering (IOE)'s broader scalability proposal. 

To maintain visibility and community alignment throughout this transition, the team shares regular progress updates through open monthly review and demo sessions, highlighting key milestones, technical discussions, and upcoming development plans.

Project handover

Leios' monthly review and demo call of September marked the handover of Leios from Input | Output Research (IOR) to IOE, transitioning the project from research to active engineering while maintaining the research and development posture.

The team confirmed a smooth transition to IOE and a continuation of monthly, community-open review and demo calls.

Proposal updates

Published in August, CIP-0164 formally proposes Leios as one of Cardano’s next major consensus upgrades. The proposal defines the protocol’s principles, objectives, and expected impact on scalability, performance, and network efficiency. Its publication marked a decisive step in transitioning Leios from research into engineering, supported by ongoing impact analyses from the consensus, ledger, and cryptography teams. Using simulators, the team studied Leios' performance under various workloads, providing first steps in validating the proposal’s design.

Since publication, CIP-0164 has attracted constructive editor and community feedback. The team is continuously providing clarifications and follow-up edits (for example, specification details and cost analyses) and will continue participating in editor meetings to align the proposal with implementation plans. During this work, a simulator bug was identified and fixed, which improved the results compared with the initial runs.

Prototype spotlight: Blink Labs (Go)

Community participation continues to drive Leios' development. Among others, TxPipe, Blink Labs, and Serokell contributed valuable reviews and analysis of CIP-0164, while the first version of the Leios development dashboard – highlighting key metrics and APIs – was presented at Token 2049.

Among these contributions, Blink Labs demonstrated early prototyping work, including:

• New certificate types for endorsement blocks (EBs)
• A shift from using a transaction body hash to a full transaction hash
• Initial block shapes for endorser and ranking blocks
• First steps toward a Leios notify mini-protocol. 

Next, the team plans to incorporate these changes into Dingo, the data node written in Go, to explore the full exchange of Leios messages and further integrate it with other prototypical Leios nodes.

Impact analysis and developer documentation

A draft impact analysis maps proposal-level changes to specific components (for example, node interfaces and client protocols). Based on the simplified proposed protocol design, the analysis indicates that most systems in the Cardano ecosystem will not be affected. Because the concrete protocol is proposed through CIP-0164, any team or component builder can begin assessing required updates and prototyping against the documented interfaces.

Performance discussion

What is the challenge? When a node restarts or catches up, it must rebuild the ledger by reapplying many EBs. If this step is slow, node readiness is delayed, and throughput suffers at scale.

How are we addressing it? Certified EBs prove they were created in the correct context, so the node can safely skip some repeat checks during reapply (for example, input-existence checks). This reduces work and speeds up the rebuild.

What is the plan? The team is progressing along two complementary prototyping and benchmarking tracks:

1. Network interaction prototypes to observe how Leios traffic integrates with the existing Cardano network.
2. Ledger-scale prototypes to stress test reapply with orders of magnitude more transactions and quantify speed-ups. The team will publish measurements, compare against the current approach, and update the implementation and operator guidance if the gains hold.

Governance and scope questions

Participants asked about differences between earlier scope statements and the current proposal (for example, elements not included in this iteration). The team reiterated that the objective remains higher throughput and that product sizing and scope adjustments will be handled transparently with the appropriate governance bodies.

What to expect next?

• Supporting specifications and conformance guidance
• Iterative prototypes, from local setups to distributed evaluations
• Public roadmap visibility via a GitHub project board as it becomes available
• Continued community discussions and editor feedback on the proposal.

Get involved

Watch the September Leios call recording on YouTube and don’t miss the next October edition:

• Date: Wednesday, October 29, 2025
• Cadence: Last Wednesday of every month
• Who: Open to the entire community

Bring your questions, feedback, and demos. We look forward to seeing you there!