A global founder program to help teams build, validate, and launch on Arbitrum
Over the past year, the Arbitrum Foundation has spent significant time working directly with developers, startup teams, and existing projects across the first Open House regions, including India and New York City.
The main signal has been consistent: there is strong founder demand for structured support around technical guidance, product validation, ecosystem access, and capital.
Open House London is the next step in that effort.
Arbitrum Open House London 2026 is a two-phase founder enablement program for teams building on Arbitrum. It is designed to help promising founders move from early ideas, prototypes, or existing products toward mainnet-ready applications and long-term onchain businesses in the programmable economy.
The program combines an online Buildathon with an in-person Founder House in London. Teams can participate in the Buildathon, apply directly to the Founder House, or do both.
Founder House London: Apply here
We encourage DAO members, delegates, ecosystem contributors, and existing Arbitrum teams to share this with founders who should be building on Arbitrum, especially teams in London, Europe, or those able to attend Founder House London in person from July 10 to 12.
Why this matters for Arbitrum
Arbitrum’s long-term growth depends on attracting and retaining high-quality founders who are building successful onchain businesses.
Open House is designed to support that goal by giving builders a more direct path into the Arbitrum ecosystem.
The program also gives the ecosystem a clearer way to identify strong teams earlier, support them more effectively, and help them continue building on Arbitrum after the program ends.
Program structure
Open House London has two phases.
Phase 1: Online Buildathon
May 25 to June 14, 2026
The Buildathon is already underway. Founders and builders are currently working toward MVP versions of their projects with support from Arbitrum ecosystem contributors.
The Buildathon gives teams a structured environment to build, iterate, and receive feedback before applying or being considered for the in-person Founder House.
Participants can attend workshops and office hours with the Arbitrum Foundation team as well as ecosystem contributors to receive feedback on early product ideation and direction.
Buildathon prize pool and grants: $115,000 USD
The Buildathon is one of the main ways promising teams will be identified for fast-track access into the Founder House in London.
Phase 2: London Founder House
July 10 to 12, 2026
The London Founder House is a curated in-person founder residency for selected teams building onchain businesses on Arbitrum.
Over three days, participating teams will work directly with Arbitrum Foundation & Offchain contributors, sponsors, ecosystem partners, and mentors. Founders should arrive with an existing project and use the Founder House to ship a meaningful new feature, sharpen their product direction, and get direct feedback from the Arbitrum ecosystem - including focused mentorship and feedback, technical, business, and product support.
Founder House prize pool and grants: $300,000 USD
The Founder House is application-based, and capacity is strictly limited to maintain a focused, high-signal environment.
Eligibility
Open House London is open to:
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Existing projects building on Arbitrum
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New ideas and early-stage concepts
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Teams exploring migration to Arbitrum
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Founders interested in building within the Arbitrum ecosystem long term
Teams may apply to either phase independently. Participation in the Buildathon is not required to apply for Founder House, although strong Buildathon teams may receive fast-track consideration.
Tracks
Both the Buildathon and Founder House feature multiple tracks, including:
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General
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Agentic AI
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Robinhood Chain-focused tracks
We expect teams to build across categories such as payments & stablecoins, tokenization & RWAs, DeFi, AI agents, privacy, consumer apps, and Arbitrum-native tech such as Stylus.
Prize distributions for winning teams will be milestone-based across all tracks except the Agentic AI categories.
Open House as a global platform
Open House London is part of a broader effort to make Open House a repeatable global platform for founder enablement across key builder regions.
In 2026, focus regions include:
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US, with New York City
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UK and Europe, with London
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Singapore
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MENA, to be confirmed
The goal is to strengthen Arbitrum’s relationship with high-quality founders across major startup and developer ecosystems, while creating a clearer pipeline for teams that want to build and scale on Arbitrum.
Looking back: Open House NYC
Open House NYC helped validate the model earlier this year.
The program saw:
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1,712 builders engaged across online and offline activations
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177 projects submitted
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$340,000 in prizes and grants distributed
More importantly, Open House NYC showed that teams were not only building speculative applications. Many were working on operational, financial, and infrastructure problems connected to institutional tokenization, coordination systems, and crypto-native service layers.
Open House London builds on those learnings with a stronger focus on founder progression, ecosystem access, and support beyond the initial build phase.