Introduction
The JAM testnet went live in January 2026, and getting there took something unusual. 43 independent teams, working in 15 different programming languages, all raced to build the same protocol from the same specification.
What JAM Is
JAM stands for Join Accumulate Machine, the protocol that Polkadot’s Relay Chain is evolving into.
Today, the Relay Chain checks and confirms the work done by the application-specific chains connected to the network, coordinates the validators who secure the whole system, runs Polkadot’s onchain governance, and routes messages between chains. JAM keeps all of that while widening what the network can actually run. Under JAM, almost any kind of computation can operate as a service on Polkadot’s shared infrastructure, not only blockchain validation. A blockchain is one kind of JAM service. So is a privacy system. An AI inference engine or a file storage layer could just as easily be another.
Gavin Wood is one of a very small number of people to have formally specified two major blockchain protocols. He wrote Ethereum’s Yellow Paper in 2014, the dense technical document that defines exactly how the Ethereum Virtual Machine behaves. In 2024 he released JAM’s equivalent, the Gray Paper, written in the same rigorous style and serving the same purpose for JAM that the Yellow Paper serves for Ethereum. Every one of the 43 competing teams builds from it.
The Prize and Why Polkadot Chose Competition
The Web3 Foundation funds development across the Polkadot ecosystem, and it set aside a prize pool of 10 million DOT and 100,000 KSM, the native token of Polkadot’s sister network Kusama, for the JAM Implementer’s Prize. Any team that builds a complete, correct implementation of the protocol earns milestone payments from that pool.
The language categories span from Category A, covering high-performance languages including C, C++, Rust, and Go, down to Category E, which includes Brainfuck and Whitespace. Those last two are programming languages built almost specifically to be hard to write in, and their inclusion is not an accident.
The structure exists to build in resilience. If one company writes all the software behind a network in one language, a serious bug in that codebase threatens the entire network at once. Spread the same protocol across 43 independent teams in 15 different languages, and a bug in one implementation is unlikely to exist in the rest. Ethereum arrived at this same conclusion after its early years and gradually pushed for multiple independent client implementations. Polkadot is building that diversity into JAM from day one instead of retrofitting it later.
The Teams and What They Are Building
Teams are building in Rust, Go, OCaml, Zig, TypeScript, Haskell, Java, Python, and more, spread across five language categories, Category A through E. Every implementation must pass conformance tests, checks that verify it behaves exactly as the Gray Paper specifies.
The Web3 Foundation administers the prize and hosts the submission process, where teams file each completed milestone for review. The Polkadot Technical Fellowship, a decentralised body of senior protocol developers, is the body that actually judges those submissions. Final prize payment is held until the Fellowship formally ratifies JAM protocol version 1.0, so every team is working toward the same externally judged, shared finish line. By January 2026, around 15 of the 43 competing teams had submitted their first milestone for review, a ratio that reflects how demanding the specification is rather than how many teams have dropped out.
The standout result so far belongs to JamZig, the Zig implementation led by developer Boy Maas. Zig is a low-level systems language most developers outside hardware or operating system work have never touched. Maas used it to build a working proof of concept that runs Solana’s Virtual Machine inside JAM, contracts calling across that boundary included. His team is now building Polana, aimed at bringing Solana’s full developer toolchain into the JAM ecosystem.
JAM’s core claim is that it can host essentially any computation as a service. A team building in an obscure language for a prize competition put that claim to a real test by porting an entirely different blockchain’s execution environment inside it, and the port ran successfully.
The Testnet and What It Enables
Since January 2026, all 43 teams have shared a public testnet to check their implementations against real network conditions rather than each team’s own isolated machine. Two environments are active, called Toaster and Tart, with Tart standing for Testing, Analysis and Research Telemetry.
Teams use both to confirm their implementations handle the protocol’s full requirements and to benchmark performance against each other. Anyone outside the competition curious what building on JAM might eventually look like can also start exploring there.
What Comes Next
Early mainnet proposals through Polkadot’s onchain governance process are targeted for Q3 to Q4 2026, an ambitious window given the scope of what’s being attempted. JAM ranks among the most complex protocol upgrades the network has taken on, Gavin Wood has said as much publicly, and there are open questions within the community about how quickly conformance reviews can move across 43 competing teams at once.
Set against that, several milestones have already landed. Multiple teams have passed conformance checks. The Gray Paper has gone through continuous refinement across 2025 and into 2026. And a team working in a language nobody expected to matter has already proven that a separate blockchain’s execution environment runs inside JAM.
What Builders Should Know Now
Nothing about JAM’s mainnet timeline is guaranteed, but there’s real preparation worth doing regardless. JAM’s compute model builds directly on coretime, the system Polkadot already uses to sell and schedule access to its validator infrastructure. Coretime is live today, so builders who learn to use it now are learning the same system JAM services will run on later. The Agile Coretime research article on this site covers how that system works in full.
The Implementer’s Prize itself is a useful thing to watch. When the Web3 Foundation starts accelerating milestone approvals and prize payments begin moving faster, that shift is the clearest public sign that JAM’s mainnet is genuinely close.
The competition has been running since April 2024, and the testnet is the first place anyone outside it can watch that work directly.