In Brief:
- Arbitrum opened a three-week online Buildathon on Sept. 14, the first phase of Open House Singapore, with $115K in prizes and grants on offer through Oct. 4.
- Winners get a guaranteed seat at Founder House in Singapore, Oct. 23-25, where another $300K is handed out. Total across both phases: $415K, all in USDC.
- At least one of the three top Buildathon spots is reserved for a project built on Robinhood Chain, which co-funds the program. There is no gaming track.
Arbitrum’s online Buildathon opened Sept. 14, putting $115K in prizes and grants in front of early-stage teams over the next three weeks.
The program runs through Oct. 4 and is phase one of Open House Singapore. Every Buildathon winner gets a confirmed spot at the second phase, a three-day in-person Founder House in Singapore on Oct. 23-25, where a separate $300K pool is awarded.
Our online Buildathon program kicks off today
Over the next 3 weeks, early-stage teams will:
> sharpen their ideas, MVPs and prototypes
> get technical, product and GTM support
> compete for $115K in prizes & spots to our in-person Founder House in Singapore
On top of that,@ArbitrumView on X ↗
Founders can apply to either phase or both. The two are funded jointly by the Arbitrum Foundation and Robinhood Chain, for $415K combined, paid in USDC.
How the $115K splits
A $70K pool goes to the three highest-placing teams. At minimum one of those three positions is reserved for a project built on Robinhood Chain.
A second category, Promising Products, carries $15K shared among its own top three. It’s aimed at teams working on AI agents and new financial primitives.
The Foundation has set aside a further $30K in USDC as grants, awarded to winning teams case by case.
Prize money doesn’t arrive in one piece. Outside the Promising Products track, awards are split 50/50 between an upfront payment and milestone-based payouts tied to technical development, product roadmap, go-to-market and user growth targets agreed with the Arbitrum ecosystem team.
Finance, not games
Neither named category is gaming-specific. The Buildathon is pitched at teams building novel financial applications on Arbitrum, and the frontier category points explicitly at AI agents.
Workshops during the three weeks cover product development, go-to-market strategy, user experience, agentic commerce, wallet infrastructure and emerging market opportunities. Teams bring an existing idea, MVP or codebase and work through repeated feedback sessions rather than starting cold.
Where the Robinhood money comes from
Robinhood Chain committed $1 million to the 2026 Open House program in February, alongside its testnet launch. That money is spread across Buildathons in New York City, London, Singapore and Dubai.
The chain’s public testnet went live in February and processed more than 200 million transactions before mainnet launched July 1.
Third stop on the circuit
Singapore is the Southeast Asia hub of the 2026 founder program. New York City and London came first, and Bengaluru has also hosted.
Those two editions drew 2,160 builders across online and in-person activations. New York took in 177 project submissions. London took 273.
Arbitrum distributed $340K in New York and $300K in London earlier this year.
The Founder House format is fixed across editions. Day one covers product-market fit, product direction and finding a wedge, with feedback from the Arbitrum Foundation, Offchain and ecosystem partners. Day two turns to go-to-market strategy, positioning and distribution. On day three teams pitch live and winners are named.
Registration for both phases runs through openhouse.arbitrum.io.
One line in the rules is easy to miss. The $30K grant pool sits entirely at the Foundation’s discretion, and it reserves the right to choose no projects at all.
