Arbitrum opens London builder program

Arbitrum has opened registration for Open House London, a three-week builder program and follow-on founder event aimed at teams launching on its blockchain network. (blog.arbitrum.foundation) The Arbitrum Foundation said applications opened on April 14 for a program that starts with an online buildathon on May 25 and ends with a three-day in-person Founder House in London in late June. Builders get workshops, product sessions, mentorship hours and live pitch sessions with teams from the foundation, Offchain Labs and ecosystem partners. (blog.arbitrum.foundation) The foundation said Open House London will put $415,000 in prizes and grants up for grabs. The program is targeting early-stage founders working on artificial intelligence, payments, decentralized finance and consumer apps that plan to deploy on Arbitrum. (blog.arbitrum.foundation, arbitrum-london.hackquest.io) Arbitrum is a Layer 2 network, which means it processes transactions in a separate system and then settles them back to Ethereum, the larger blockchain underneath it. The pitch to developers is lower fees and faster execution than using Ethereum alone. (arbitrum.io, offchainlabs.com) Open House is part of a broader 2026 recruiting push by Arbitrum to bring in more developers through regional events, online buildathons and in-person founder houses. The program website lists New York, Dubai, London and Singapore as stops on this year’s tour. (openhouse.arbitrum.io, luma.com) Arbitrum has pointed to New York as proof of concept for the format. In a foundation update published on April 15, it said the New York cohort drew more than 1,700 builders, produced 177 projects and awarded $340,000 across categories including payment rails, prediction markets and tokenized assets. (blog.arbitrum.foundation) The London push also lines up with Arbitrum’s effort to tie its developer funnel to large partners building on the stack. Robinhood said in February that it is committing $1 million to the 2026 Open House program and will participate in buildathons in New York, Dubai, London and Singapore. (robinhood.com) That partnership matters because Robinhood’s new chain runs on Arbitrum technology, giving Arbitrum a way to pitch builders on distribution as well as infrastructure. The company said the public testnet launched with support from ecosystem partners including Alchemy, Chainlink, LayerZero and TRM. (robinhood.com) For Arbitrum, the London program is the next test of whether prize money, mentorship and in-person access can turn hackathon projects into apps that stay on its network after the event ends. (blog.arbitrum.foundation, openhouse.arbitrum.io)