On August 1st, Simplicity activated on the Liquid Network, unlocking smart contracts that are formally specified and built from first principles. The milestone follows nearly a decade of research and development by Blockstream Research. In a recent conversation between the Simplicity creators and the StarkWare team, Blockstream CEO Adam Back said, “Simplicity is making things simpler by being verification only. It doesn't have to run the program.”
A Language for Verification, Not Execution
“If you can compute something in a finite amount of time, you can do it in Simplicity,” explained Andrew Poelstra, Director of Research at Blockstream. “Any validator can scan through it extremely quickly and determine exactly how much memory and exactly how much time it's going to take.” Unlike traditional scripting systems, Simplicity programs are composed from nine combinators and are encoded as mathematical functions. “It's a language defined almost in terms of pure mathematics and the most basic building blocks of computer science,” said Poelstra.
Predictable Behavior. No Surprises.
Where systems like the EVM allow for unpredictable behavior due to mutable state and race conditions, Simplicity aims for precision. Speaking about EVM-based designs, Adam Back said, “You have a form of language where machines are speaking to each other, and it’s a known factor that it gets extremely complicated.” By contrast, Simplicity gives developers the ability to specify and formally prove contract behavior. “You can potentially make some predicates you care about. The only way the money in this contract can be spent is like this. And you could prove that's true,” he said.
Simplicity mainnet launch, the future of Bitcoin programmability, and the synergy with STARKs
STARK Integration and Real Applications
StarkWare has already integrated Simplicity by building a STARK verifier directly in the language. “It shows you you can do an enormous number of very flexible things with Simplicity and do it with high assurance,” said Back. Abdel from StarkWare added, “We did not want to transform the EVM to a ZKVM because we knew from the beginning that it was not ZK friendly.” This integration demonstrates how Simplicity can support advanced use cases and opens the door to ZK rollups, upchains, and verifiable Bitcoin-native applications.
Thrilled to be collaborating with @Blockstream on Simplicity, a new Bitcoin scripting language.
— StarkWare 🐺🐱 (@StarkWareLtd) August 4, 2025
Among the first to experiment with it, we're combining it with STARKs to explore Bitcoin scaling like never before.
Discover what this powerful combo can unlock:… pic.twitter.com/JA1e8qMco6
Emulating Bitcoin Opcodes Without Soft Forks
With Simplicity, developers can implement proposed Bitcoin opcodes like OP_CAT or OP_VAULT without needing consensus changes. “And Simplicity, unlike Bitcoin script, it's not limited in any computational way,” said Andrew Poelstra. “In Script, you can only do a little bit of arithmetic and do a couple specific crypto opcodes. In Simplicity, if you can compute something in a finite amount of time, you can do it in Simplicity.” This opens the door for developers to prototype contract behavior that has historically required long-term soft fork coordination.
Developer Tools Are Live
Simplicity is now live on Liquid mainnet and available for experimentation through SimplicityHL, a high-level developer-friendly language that compiles to Simplicity. The ecosystem includes a compiler, an in-browser IDE, contract examples, and formal documentation for jets and primitives. “Using Simplicity Shell was a really fun experience because you feel really early,” said Michael Zaikin from StarkWare. He added, “I think it's a really good stage for developers to tap into Simplicity and try to build stuff because it's pretty powerful.”
Developers can start building today at simplicity-lang.org and join the conversation on Telegram.