The event is co-sponsored by Robinhood Chain, a Layer 2 network built on Arbitrum's technology, and is the second active city in a global series following New York City. The series has committed $1.8 million in total prizes across its participating cities; a Dubai leg was originally announced but has since been postponed indefinitely. Alchemy, a developer platform and node infrastructure provider, has also joined as a sponsor. Applications are open at arbitrum-london.hackquest.io.

The London prize pool is structured across two phases. The online buildathon portion carries $115,000: $70,000 for open-category projects, $15,000 reserved for AI and agentic applications, and $30,000 in grants. The Founder House phase holds the larger share at $300,000, split between open categories ($120,000), Robinhood Chain-specific awards ($90,000 across a $60,000 Founder-in-Residence track and a $30,000 Innovation Award), AI and agentic projects ($20,000), and grants ($70,000). The Foundation describes the London pool as its largest to date. For context, the preceding NYC Founder House distributed $340,000 across 55 submitted projects out of 473 original applications; the NYC buildathon phase carried its own separate prize allocation, making the combined NYC program total higher.

Robinhood Chain's presence as a co-sponsor reflects a broader strategy. The company committed $1 million to Arbitrum Open House builders across all 2026 cities. Its London-specific categories, the $60,000 Founder-in-Residence award and the $30,000 Innovation Award, are exclusively for projects deploying on Robinhood Chain; at least one top-three placement in competitive categories is reserved for Robinhood Chain projects. The chain recorded 4 million testnet transactions shortly after its public testnet launched earlier this year, signaling early developer interest. Robinhood has described its ambition for the chain as bringing retail investment activity onchain.

Beyond the event itself, three technical developments covered in Builder's Block #017 point toward where Arbitrum's developer focus is heading. The first is x402, an open payments standard pioneered by Coinbase that repurposes a long-dormant HTTP status code (402 Payment Required) into a functional payment mechanism for AI agents and automated software. When a client requests a protected resource, the server returns a 402 response with payment terms. The client generates a signed payment payload and retries the request. The whole cycle settles onchain in under two seconds at a cost of roughly $0.0001 per transaction. The protocol is live on Arbitrum, Base, Polygon, and Solana. Arbitrum's developer relations lead Ben Greenberg has published a working integration with AWS infrastructure, and Amazon announced a managed x402 service through Amazon Bedrock AgentCore Payments in spring 2026, a sign that the pattern is being adopted beyond crypto-native tooling.

The second development involves ZeroDev, a smart account infrastructure provider that Offchain Labs acquired earlier this year. ZeroDev has enabled over 5 million smart accounts across more than 30 networks. Its core tools, including gasless transactions, session keys, and paymasters (mechanisms that let applications cover transaction fees on behalf of users), are central to building applications that do not require users to hold tokens just to interact with a product. Steven Goldfeder, CEO of Offchain Labs, described ZeroDev's team as bringing "rare expertise in developer infrastructure." ZeroDev CEO Derek Chiang noted that the acquisition allows the combined team to "tackle UX at all stack layers, from UI down to the chain itself." The third development is B3OS, an automation engine that integrates directly with ZeroDev. B3OS ships with more than 20 pre-built workflow templates and a visual no-code builder called Caddie, which is designed to lower the barrier for developers building agentic applications on Arbitrum infrastructure. Separately, Offchain Labs has introduced "Offchain" as an institutional-focused brand targeting onchain solutions for enterprise and institutional clients.

For developers outside the United States, several of these updates carry direct relevance. The Open House buildathon phase is fully remote, meaning builders in South Asia, Africa, and Southeast Asia can participate without travel. The in-person Founder House in London will require relocation for those selected. The Dubai leg of the Open House series has been postponed indefinitely due to regional security concerns, removing what would have been a more accessible venue for developers in South Asia and the Middle East and North Africa region. Africa's developer community already has a significant footprint in the Arbitrum ecosystem: Nigeria is a founding region of the Arbitrum Ambassador Program, alongside India and Mexico, and the program has generated more than 122 million impressions since August 2024.

The x402 micropayment model and the ZeroDev gasless transaction stack both address real friction points in markets where traditional payment infrastructure is unreliable or expensive, and where gas fee friction is a documented barrier to adoption for new users. The Arbitrum Mentorship Program's first cohort reflects the scale of developer interest in this space. Selected from more than 900 applicants, 13 projects were chosen across DeFi, AI, payments, and real-world asset categories. The program runs for eight weeks, pairing participants with mentors through biweekly one-on-one sessions, and culminates in a Demo Day with a $100,000 prize pool judged by representatives from Pantera Capital, Electric Capital, and Lightspeed. Two cohort projects carry explicit emerging-market mandates: Capa, a cross-border payments platform reporting $150 million in monthly payment volume, and Reinforce.fi, a self-custodial yield platform designed for emerging-market users.

ARB, Arbitrum's governance token, trades at approximately $0.14 with a circulating market cap near $879 million and a fully diluted valuation of around $1.43 billion, based on data available at time of publication. A token unlock of 92.65 million ARB (roughly $13.2 million at current prices) is scheduled for May 16. Arbitrum holds an estimated 40 to 44 percent of total Layer 2 TVL by DefiLlama metrics, with TVL in the $15.9 billion to $16.9 billion range. Combined, Arbitrum and Base account for approximately 77 percent of all Layer 2 DeFi liquidity, underscoring the network's dominant competitive position.

The Singapore Founder House has not yet been formally dated, but it is expected to serve as the final stop in the 2026 series. Earlier communications from the @ArbitrumDevs account referenced four global cities in connection with the rollout, suggesting the series structure may be revised as scheduling for additional cities develops.