Cardano (ADA) activated the Leios testnet on June 23, targeting a 65-fold increase in transaction throughput, according to a research report by MEXC Ventures. The upgrade aims to raise monthly transaction capacity from roughly 800,000 to 27 million, with a mainnet hard fork planned for Q4 2026 if testing proceeds as scheduled.
Structural Overhaul to Break Throughput Bottleneck
The Leios testnet launch comes about a month after community approval on May 25. Input Output (IO), Cardano's development arm, is redesigning the blockchain's processing architecture to eliminate speed bottlenecks. Currently, Cardano operates on a single-block production model where only one validator can propose a block at a time, limiting throughput to around 10 transactions per second and making it difficult to scale under high demand.
MEXC Ventures noted that Leios differs from conventional scaling approaches like increasing block size or reducing block intervals. Instead, it separates block functions: endorser blocks collect transaction data, while ranking blocks determine the final order. Multiple validators can create endorser blocks simultaneously, enabling parallel processing, while ranking blocks reference them to maintain orderly settlement.
UTXO Sharding and Phased Testing
Leios also introduces UTXO sharding, distributing the ledger's unspent transaction outputs across multiple shards for concurrent processing. This reduces bottlenecks while preserving Cardano's existing UTXO model. IO product manager Carlos Lopez de Lara stated that the initial testnet will start at 2x to 5x current throughput, gradually increasing to the 65x target based on load and stability tests.
The development scale is unprecedented: Leios codebase exceeds 705,000 lines as of June, the largest single upgrade in Cardano's history. Testing will include high-load scenarios, system failures, and simulated attacks. IO plans to proceed with the mainnet hard fork in Q4 2026 after thorough validation.
A Strategic Bet on Scalability
Industry observers view Leios as Cardano's structural gamble on the blockchain trilemma—balancing scalability, decentralization, and security. By splitting block roles, Cardano aims to boost speed without compromising its core principles. The success of Leios hinges on whether testnet performance can be replicated on mainnet while maintaining decentralization and security. If successful, Leios could become a reference design for next-generation public blockchains.