Flexathon

Flexathon [ /‘flɛksəθɔn/ ] was a solo hackathon run by Dan Hughes, founder of Radix, over his vacation in late 2020. Its stated mission, set out in his public diary, was to have “a working demonstration of some the fundamental technology innovations myself and the Radix team have been pioneering” by 11 December 2020 — specifically, atomicity and composability across shards under the Cerberus consensus protocol.

The result was demonstrated in a Radix Labs session, Radix Founder Demonstrates Cross Shard Atomic Composability, published on 19 May 2021.

The brief, and why it was set

Hughes gave two reasons for spending vacation time on it. The first was simply that he missed doing hackathons. The second was adversarial: the Cerberus paper — Cerberus: Minimalistic Multi-shard Byzantine-resilient Transaction Processing, co-authored with Jelle Hellings, Joshua Primero and Mohammad Sadoghi and submitted to arXiv on 10 August 2020 — had been public for three months, and in his words “some in the crypto community has been spreading doubt. So, enough of quietly working, time to flex some of our tech!”

The scope was set deliberately narrow. The diary describes the build as “an independent implementation of Cerberus which is intended to showcase the possibilities of atomicity and composability in a sharded environment”, assembled from a mix of existing Radix core code, earlier Tempo and CAST work, components of Hughes’ own R&D framework, and new code written for the occasion. It also carried an unusually blunt disclaimer for a founder demo: the prototype “WILL be buggy, it WILL crash, it will NOT be commercial grade, unit tests will be minimal and some of the code patterns will be questionable”, and it would “not bear any resemblance to any of the networks planned for release on our roadmap, other than exhibiting the fundamentals of the Cerberus protocol”.

What the public diary records

The diary was published as a running log rather than a write-up — “a direct feed from me… full strength, non-filtered Dan incoming” — with each day given a topline, a “The Good” column and a “Challenges” column. Three days were recorded before it stopped:

• Day 1 (23 Nov) — preparation. Collating the networking, database, event-handler and cryptographic primitives to build on top of.
• Day 2 (24 Nov) — connectivity between nodes, simple atoms and particles, basic gossip; atoms could be sent around the network.
• Day 3 (25 Nov) — atom pool voting implemented and tested at a network size of 32 nodes, with a start made on block generation and a proof-of-work implementation.

Days 1 and 2 each closed with a short video posted to Hughes’ Twitter account, linked from the diary.

The primary record and its gaps

Almost everything publicly checkable about the Flexathon comes from two artefacts, and both are incomplete.

The diary is the primary source, and it is 4,214 characters long and ends at Day 3 — three days into a nineteen-day run. Nothing in the public document covers the remaining sixteen days, the cross-shard atomicity milestone itself, or whether the 11 December deadline was met. Descriptions of the Flexathon that list “node connectivity, sending atoms, pool voting, early block production and proof-of-work” as its output are therefore describing the first three days, not the project.

The diary names github.com/DanoshiFusermoto/hackation as the third of its four follow-along sources. That repository returns 404. Hughes’ GitHub account carries two public repositories today — Hyperscale (created March 2025) and a fork of Apache Milagro — and neither is the Flexathon build. No public copy of the prototype’s source is known to survive.

One archived capture of the repository page survives, and it is dated Day 1. The Internet Archive holds a single successful snapshot of github.com/DanoshiFusermoto/hackation, taken on 23 November 2020 at 21:45 UTC — the evening of the diary's first day. It records a repository already at 49 commits on master, with one branch, no tags, no releases, no description and no topics; two watchers, no stars, no forks; a single top-level entry named core; and a latest commit message reading “Added empty atom to genesis block to solve NPE”. Its language breakdown is Java 100%, consistent with the diary's account of a build assembled from existing Radix core code rather than written from nothing, and a reminder that the Flexathon shares no lineage with the Rust hyperscale-rs work that carries sharding today.

The capture is the landing page, not the tree, so it does not recover a single line of the source. The archive's next visit, on 21 December 2022, records a redirect rather than a page — placing the repository's removal between those two dates. Barring a private copy, the prototype's code should be treated as lost.

What does survive is the demonstration: a 46-minute Radix Labs recording published on 19 May 2021, five months after the deadline the diary set.

What it did and did not lead to

The Flexathon achieved what it was built to achieve: a running, if fragile, demonstration that atomic composability across shards was implementable, at a moment when the claim rested on a whitepaper and an academic paper rather than on code.

It is worth being precise about what followed, because the prototype is sometimes described as a foundation for the network that shipped. Olympia, the first Radix public network, launched on 28 July 2021 running Radix Engine v1 and unsharded consensus with a single shard group. Alexandria (15 December 2021) came after Olympia, not before it, and was a Scrypto developer environment rather than a mainnet. Babylon (28 September 2023) also runs a single shard group.

The cross-shard atomic composability the Flexathon demonstrated in December 2020 has, in other words, never run on a Radix production network. Multiple shard groups are scheduled for Xi’an, dated 2027, and the sharded execution work now proceeds in hyperscale-rs rather than from any Flexathon code. Hughes’ own diary anticipated the distinction: the prototype was never meant to resemble the roadmap networks, only to prove the fundamentals were real.

External links

• Flexathon diary — Dan Hughes (Google Docs)
• Radix Founder Demonstrates Cross Shard Atomic Composability — Radix Labs (YouTube, 19 May 2021)
• Cerberus: Minimalistic Multi-shard Byzantine-resilient Transaction Processing — arXiv (10 Aug 2020)
• DanoshiFusermoto — GitHub (Dan Hughes)