Aptos has switched its blockchain to a new default engine for processing transactions. Block-STM v2, the upgraded version of the network’s parallel execution system, now runs by default on the Layer-1 chain.
Most users will never notice the change. That is sort of the point: the upgrade happens under the hood, and neither users nor decentralized applications need to do anything.
How Block-STM v2 works
The technical term for this is optimistic concurrency control. The engine executes transactions speculatively across multiple processor threads at the same time.
It then checks each transaction’s read and write sets, meaning the data it looked at and the data it changed. Those sets are validated against an ordering that consensus has already fixed in advance.
When two transactions conflict, only those specific transactions are re-executed. The final result is deterministic and serial-equivalent.
One feature stands out for developers. The v2 engine handles parallel execution dynamically, without requiring upfront access lists or dependency declarations.
The numbers behind the upgrade
The original Block-STM already set a high bar. In 2022 benchmarks, v1 hit roughly 170k transactions per second.
Those same tests showed it running 17x faster than sequential execution when using 32 threads.
Version 2 aims further up the hardware ladder. Its refinements focus on multi-core scaling, targeting performance across up to 256 cores.
Aptos announced Block-STM v2 in October 2025 as part of its roadmap. The stated goal was better performance for high-frequency DeFi workloads, the kind of traffic where trading bots and liquidations hammer the same contracts at the same moment.
Updates in 2026 confirmed that v2 is now enabled by default, alongside additional performance optimizations and consistency fixes. The rollout spans execution, consensus, storage and state sync processes.
Background: a homegrown idea that spread
Parallel execution has been central to the Aptos pitch since its mainnet launched in October 2022.
The idea did not stay inside Aptos. Other blockchain systems, including certain implementations of the Cosmos SDK, have adopted or forked variants of the original Block-STM approach.
What this means for Aptos and its ecosystem
For developers, the most practical change is the absence of friction. No new access lists, no dependency declarations and no migration work are required to benefit from the faster engine.
For DeFi specifically, the upgrade targets a known pain point. High-demand workloads tend to create conflicts because many users interact with the same pools and contracts simultaneously. An engine that re-executes only the colliding transactions could help Aptos handle those bursts more gracefully. The research behind the upgrade also emphasizes keeping transaction costs low for users while throughput rises.
Still, benchmark numbers and real-world performance are different animals. The 170k TPS figure came from 2022 benchmarks of v1, and lab conditions rarely match the messiness of live network traffic.
Scaling toward 256 cores raises questions about what validators will need to run in order to capture those gains, and how that shapes who can participate.
Disclosure: This article was edited by Estefano Gomez. For more information on how we create and review content, see our Editorial Policy.