Cardano's protocol developer Input Output Global opened the Ouroboros Leios testnet to external developers on June 23, 2026, giving them their first access to Cardano's next-generation consensus protocol outside the core research team.
Cardano has operated at roughly 800,000 monthly transactions under its current protocol, a throughput ceiling that leaves the chain well below faster L1 networks. Leios is the proposed fix: a redesigned block production architecture that runs multiple processing pipelines in parallel rather than sequentially. IO's stated target is a roughly 33-fold increase in capacity, to more than 27 million monthly transactions. The public testnet is the first live environment where that architecture faces real network conditions rather than simulation.
Development spans more than 705,000 lines of code across 5,700 technical updates. IO founder Charles Hoskinson said: "We've done things that we could only have dreamed of when I started the project." IOG published a technical interview on Leios with product manager Carlos Lopez De Lara on June 22, the day before the testnet opened.
Cardano's delegated representative system cleared funding last month. Over 84% of DReps approved the core governance proposal, releasing 27.7 million ADA from the community treasury to fund Leios through mainnet maturity. Five companion proposals also passed: the Cardano Maintenance Initiative, Cardano Upgrades, Developer Experience Initiative, Higher Assurance Technical Collaboration, and Plutus improvements. The Plutus improvements proposal carried an additional 11.8 million ADA for smart contract enhancements.
IO indicated the upgrade could reach mainnet by end of 2026, advancing Leios from prototype to mainnet-ready through Software Readiness Levels 5 through 8.
ADA was trading at approximately $0.185 at launch, 94% below its September 2021 all-time high of $3.09.
