Registration is live at arbitrum-london.hackquest.io. The online buildathon runs from May 25 to June 14, 2026, and is open to all registered teams. The in-person Founder House follows on June 25 to 28 in London, with June 25 designated as an arrival day and the three-day sprint running June 26 to 28, limited to application-selected founders. Together, they form the second leg of a series that began in New York City in March and will continue with stops in Dubai and Singapore later this year.

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Prize Structure and Format

The $415,000 London prize pool is split between the two phases. The buildathon carries $115,000: $70,000 for the open category, $15,000 for AI agentic projects, and $30,000 in grants. The Founder House offers the larger share at $300,000, including $120,000 in the open category, $20,000 for AI agentic projects, $70,000 in grants, and $90,000 across two Robinhood Chain tracks (a $60,000 Founder-in-Residence award and a $30,000 Innovation Award).

Robinhood Chain, a public testnet built on Arbitrum infrastructure (currently operating as a pre-production network), is a co-sponsor across the full 2026 series. The platform has committed $1 million in prizes across all four cities, out of a total programme prize pool of $1.8 million. The London Founder House is structured as an application-only, in-person sprint featuring technical workshops, product sessions, mentorship hours, and live pitches to partners including the Arbitrum Foundation, Offchain Labs, and ecosystem collaborators.

The Arbitrum Developers account described the programme on X: "Not a hackathon, not a hacker house, but a global program built for founders who are serious about shipping." That quote originates from the Foundation's official social media account rather than a named individual; no named Foundation spokesperson was quoted specifically about the London edition, and no dedicated press release was issued beyond the Foundation's blog post.

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NYC Set the Baseline

The New York City edition, which concluded in March, provides the clearest picture of what London participants can expect. The Foundation received 473 applications, accepted 88 teams, and distributed $340,000 in prizes. Across the full NYC Open House (including the buildathon), the Foundation reported 1,712 builders engaged across 177 projects.

Top NYC winners included Kustodia, which took $60,000 for escrow-style crypto payment infrastructure; Tilt Protocol, which received $100,000 from the Robinhood Chain track for its AI-driven real-world asset management product; EqualFi, which received $20,000 for tokenized real-world asset infrastructure; and Bond.Credit, which received $50,000 for a capital markets protocol. Sessions in New York were led by teams from Dune, Uniswap Labs, Alchemy, LayerZero, GMX, Robinhood Chain, and Fhenix, among others.

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What London Means for Non-US Builders

London is the first stop outside the United States, and that matters for builders who have found New York logistically or financially out of reach. The city draws a large South Asian diaspora with deep roots in fintech and financial services, and it has historically been a primary entry point for African founders seeking venture capital and institutional partnerships, particularly those from Nigeria, Ghana, Kenya, and South Africa.

The programme's emphasis on payments infrastructure, real-world asset (RWA) tooling, and DeFi access maps directly to use cases that have demonstrated traction in both African and South Asian markets. RWAs are tokenized versions of traditional financial instruments such as bonds, receivables, or real estate held on a blockchain. Builders focused on remittances, cross-border transfers, or financial access for underbanked populations will find the thematic categories relevant to their work. It should be noted that no specific Arbitrum Foundation outreach to South Asian or African builder communities has been documented at time of research; the case for London's relevance to those communities rests on the city's role as a geographic and financial hub, not on confirmed Foundation targeting.

UK regulatory conditions add another layer of context. From January 1, 2026, crypto firms operating in the UK have been required to collect and report user transaction data under the OECD's Cryptoasset Reporting Framework (CARF). A broader FCA licensing regime for cryptoasset businesses is expected to follow in late 2026. The compliance burden is real, but the regulatory trajectory appears to be producing greater institutional legitimacy, which appears consistent with the profile of builders the Open House programme is designed to attract.

Builders based in South Asia or Southeast Asia who cannot access London should note that Singapore is the fourth and final stop. No dates or registration details have been announced for the Singapore leg at time of publication.

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Token and On-Chain Context

The Foundation is running this expansion against a backdrop of significant ARB token pressure. ARB, the governance token for the Arbitrum network, was trading at approximately $0.11 as of April 12, 2026, with a market cap near $686 million. A scheduled unlock of 92.65 million ARB tokens on April 16 adds roughly $10.4 million in new supply at current prices. Arbitrum One holds approximately 30.86% of the total L2 market by total value locked (TVL), a measure of assets deposited in protocols on the network. TVL peaked at $8.6 billion on Arbitrum One in August 2025; current figures should be verified against DefiLlama before drawing conclusions about network health.

Deploying ecosystem grants and prizes through programmes like Open House is one common approach for blockchain foundations looking to drive protocol utilisation when token prices are under pressure.

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What Comes Next

After London, the series moves to Dubai and then Singapore. Dubai's stop is expected to draw builders from the MENA region, where the UAE's Virtual Assets Regulatory Authority (VARA) has provided a comparatively permissive but structured licensing framework. Dubai event dates have not been confirmed at time of publication.

Singapore will serve as the anchor for South and Southeast Asian outreach.

Teams that win prizes at the London Founder House may also gain access to the Arbitrum Mentorship Programme, a separate eight-week, equity-free initiative that launched on April 13, 2026. It accepts up to 15 teams, awards $100,000 in non-dilutive prizes at Demo Day, and includes introductions to investors such as Pantera Capital, Electric Capital, and Lightspeed. NYC Open House winners received automatic invitations to the programme. It is unclear whether London winners will receive the same automatic pathway; readers should check the programme terms directly for confirmation.

Builders entering through Open House will also be working on an upgraded network. The ArbOS Dia upgrade delivers improved fee management, increased throughput, passkey-based onboarding, and Ethereum Fusaka compatibility, representing a meaningful improvement to the technical environment available to teams building on Arbitrum.

Registration for the London buildathon is open now at arbitrum-london.hackquest.io. The online phase closes June 14, 2026, and Founder House applications are reviewed on a rolling basis.