Arbitrum Open House London: Online Buildathon
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I am preparing for Arbitrum Open House London: Online Buildathon. Help me understand the rules, required developer resources, project ideas, and a 7-day preparation plan based on my HackQuest builder journey.
Host by
Arbitrum Foundation
Hackathon Mode
ONLINE
Ecosystem
Conduct
View Code of Conduct (External Link)
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Tech Stack
Participants
115,000 USD
Available in Prizes
Description
Arbitrum Open House London — Buildathon
London is where startups, capital, and real-world adoption meet.
Arbitrum has infrastructure trusted by institutions and used by millions.
It’s time to connect the two.
The Open House London Buildathon brings three weeks of intensive building using the same tech stack that BlackRock and Robinhood bet their reputations on.
Three weeks to build something that matters.
DeFi. Gaming. Social Applications. DePin. Something entirely new?
That’s up to you.
Build with Stylus in familiar languages, or with Solidity. Deploy on Arbitrum One or a custom Arbitru chain.
Bring an existing project or start from scratch.
No compromises. No limits. Just build.
And there’s plenty to play for.
The top three teams will each win a place at the IRL Founder House in London in June. Four days of intense working with Arbitrum’s technical team and successful ecosystem founders.
Real mentorship, real connections, real paths from idea to funding.
We've built the infrastructure. You bring the vision.
Let's see what happens next.
Agenda & Google Calendar
Get access to the workshops & feedback sessions by navigating to the "Workshops & Sessions" tab.
Find the Buildathon schedule below.
Overall prize
70,000 USDC
Overall prize
Overall prize
Judging Criteria
Your project must be deployed on an Arbitrum chain to qualify. For example: Arbitrum Sepolia, Arbitrum One, Robinhood Chain, or others.
Projects are assessed on the following criteria:
Smart contract quality - code following best practices, structured logically and efficiently, with minimal security vulnerabilities
Product-Market Fit - projects with clear potential to attract and retain users
Innovation and Creativity - original approaches that push boundaries
Real Problem Solving - applications that address genuine market needs
Note:
At minimum, 1 of 3 prizes is reserved for a project building on Robinhood Chain
At minimum, 1 of 3 prizes is reserved for a project building on Arbitrum
All prizes are subject to development-tied milestones. Please refer to our Terms and Conditions for details.
Best Agentic Project
15,000 USDC
Best Agentic Project
Best Agentic Project
Judging Criteria
Your project must be deployed on an Arbitrum chain to qualify. For example: Arbitrum Sepolia, Arbitrum One, Robinhood Chain, or others.
Projects are assessed on the following criteria:
Smart contract quality - code following best practices, structured logically and efficiently, with minimal security vulnerabilities
Product-Market Fit - projects with clear potential to attract and retain users
Innovation and Creativity - original approaches that push boundaries
Real Problem Solving - applications that address genuine market needs
Note:
At minimum, 1 of 3 prizes is reserved for a project building on Robinhood Chain
At minimum, 1 of 3 prizes is reserved for a project building on Arbitrum
Grants
30,000 USDC
Up to $30k USDC in milestone-based grants for selected projects
We reserve the right to distribute milestone-based grants to selected projects on a case-by-case basis. You are not guaranteed to be selected, and we reserve the right to not select any projects for this.
Grants
Judging Criteria
We reserve the right to distribute milestone-based grants to select projects on a case-by-case basis. You are not guaranteed to receive a grant, and it is at the sole discretion of the Arbitrum Foundation to choose grant recipients. We reserve the right to not select any projects for grants.
Schedule
Resource
Developer Documentation
Hey Open House London builders! We have compiled a list of useful information for you below. Please take a thorough look as most of the information you will be looking for will be covered here.
Faucets
Ethereum Sepolia - claim testnet ETH, then bridge it to Arbitrum Sepolia using the bridge.
https://sepoliafaucet.com/
https://arbitrum.faucet.dev/
https://www.infura.io/faucet/sepolia
https://sepolia-faucet.pk910.de/
Arbitrum Sepolia - just claim testnet ETH and you're ready to go:
https://arbitrum.faucet.dev/
https://faucet.quicknode.com/arbitrum/sepolia
https://www.l2faucet.com/arbitrum
Arbitrum Sepolia USDC Faucet:
https://faucet.circle.com/
Robinhood Chain Faucet:
https://faucet.testnet.chain.robinhood.com/
RPC Endpoints
Useful Tools for Builders
Arbitrum Docs: https://docs.arbitrum.io/
Arbitrum SDK: https://github.com/OffchainLabs/arbitrum-sdk
Stylus Docs: https://docs.arbitrum.io/stylus
Stylus By Example: https://stylus-by-example.org
Stylus CLI: https://github.com/OffchainLabs/cargo-stylus
Stylus Rust SDK: https://github.com/OffchainLabs/stylus-sdk-rs
OpenZeppelin Rust Contracts: https://github.com/OpenZeppelin/rust-contracts-stylus
OpenZeppelin Solidity Contracts: https://github.com/OpenZeppelin/openzeppelin-contracts