Builder's Block #016: Open House London Dates Locked & First Cohort of Mentorship Program

📣 Announcements

Key updates from the Arbitrum ecosystem and Foundation.

Everything you need to know for Open House London

Applications for Open House London are still open. It kicks off with a 3-week online Buildathon, running from May 25 - June 14, where teams can go from idea to product with $115K in prizes and grants up for grabs.

The journey continues with an in-person Founder House in London from July 10-12, bringing together top builders to compete for an additional $300K while refining, shipping, and launching in the programmable economy on Arbitrum.
➡️Check out the Buildathon's prize breakdown & Apply now

13 teams have been selected for the Arbitrum Mentorship Program

900+ teams applied to the Arbitrum Mentorship Program - 256 DeFi, 153 infra, 120 AI, 110 payments, 88 RWA. Builders aren’t experimenting anymore, they’re committing across every vertical that matters, and they’re choosing to build and launch real products into the programmable economy on the Arbitrum platform.

13 teams have been selected for Cohort 1, each entering an 8-week program of hands-on mentorship, operator-led workshops, and direct access to leading investors and ecosystem partners, all focused on getting to launch.
➡️ Read more about the teams

Winners for the ArbiLink Agentic Bounty Announced

The ArbiLink Agentic Bounty blew past expectations. We've recieved so many strong submissions and picking winners wasn’t easy. But here they are. The Top 3 winning projects each get $250 in prizes, and one project gets a sponsored trip to Open House London!
➡️ Meet the winners and check out their projects

📚 Learn & Build

New learning drops and hands-on resources from across the Arbitrum ecosystem.

The Rise of Agentic Payments & how Arbitrum Fits In

Agentic payments are becoming a requirement. With Cloudflare rolling out agent-readiness scanners that surface standards like x402, the shift toward machine-native payment flows is already underway. Arbitrum provides the speed, low costs, and liquidity needed to make these flows viable at scale. This blog breaks down what’s changing and how to build for it.
➡️ Read more in the article

Building Secure Key Management for AI Agents

Learn how to securely manage keys for AI agents with a process-isolated KMS built on top of @OpenWallet. Instead of exposing private keys, agents are issued scoped tokens while signing happens in fully isolated infrastructure, keeping secrets out of the same environment as your LLM. A more secure, production-ready approach for teams building agentic workflows onchain.
➡️ Read more in the article

🔦 Ecosystem Highlights

Fresh launches and standout threads from around the Arbitrum ecosystem.

Global Markets are Becoming Programmable

Global markets are becoming programmable, where access, settlement, and coordination are defined in software instead of intermediaries. This is turning financial infrastructure into composable building blocks for faster, more flexible markets. But enterprise adoption depends on execution, reliability, and scale.

Arbitrum is where this becomes real: a finance-native execution layer powering programmable markets with the performance and liquidity institutions need.
➡️ Read more in the blog

🛠️ Dev Tooling & Infra

Updates to SDKs, CLIs, and developer workflows across the stack.

Meet ARBuilder: your AI dev teammate on Arbitrum

A new tool just came to town built by Quantum3Labs (the same team behind Scaffold Stylus). If you’re building on Arbitrum, here’s an easier way to ship faster. ARBuilder lets you describe what you want - Stylus contracts, bridges, dApps, Orbit L3s - and you'll get working, verified code ready to use.

Powered by 19 specialized tools, live docs, and a 3-stage reranking pipeline, it keeps outputs accurate, up-to-date, and compile-ready across Cursor, VS Code, Windsurf, Claude Code, and its web playground. From idea to deployment, without the usual friction.
➡️ Read the full technical breakdown & Try it youself

🧵 Forum & Community Discussions

What builders are debating and proposing this week.

ERC-8063 Reference Implementation on Arbitrum One

A new proposal that brings ERC-8063 (Groups: Membership Tokens) to Arbitrum One through a full reference implementation. ERC-8063 defines a membership-token primitive for token-gated access, enabling use cases like loyalty programs, governance tiers, and membership-based systems. Relevant if you’re building token-gated apps, onchain loyalty systems, or composable access layers.
➡️ View Proposal

[Constitutional] AIP: Approve Release of Frozen ETH

Following the rsETH (KelpDAO) exploit, the Arbitrum Security Council acted quickly on April 21 to freeze ~30,765 ETH tied to the attacker, marking a major moment in onchain incident response.

A new governance proposal now suggests releasing these funds into a coordinated recovery effort led by ecosystem teams like Aave, LayerZero, and others, highlighting how Arbitrum’s governance can step in to support users and reinforce the system in real time.
➡️ View Proposal

March 2026 Security Council Election: Member Election

The Arbitrum Security Council elections are underway, with the final Member Election phase running until May 3; delegates are now voting to select the next cohort responsible for critical security decisions, making participation especially important following recent events.
➡️ Find out how to cast your votes

That’s all from Builder’s Block #016. Thanks for reading - and keep building. Arbitrum Everywhere.