Builder's Block #017: $415k in Prizes at Open House London - Apply Now

📣 Announcements

Key updates from the Arbitrum ecosystem and Foundation.

$415,000 in Prizes & Grants at Open House London

Open House London, a global builder program + startup accelerator designed for founders to help them launch new businesses into the programmable economy on the Arbitrum Platform, features $415k in total prizes (our biggest pool to date). This video covers the full program and prize breakdown along with project ideas that we're looking for.

Open House London is kicking off with Buildathon on May 25th - a 3-week, online global program helping early-stage teams turn ideas into onchain products on Arbitrum.
➡️ Apply for the Online Buildathon Now!

Open House London Sponsor Spotlight - Alchemy

We're excited to welcome @Alchemy as a sponsor of Open House London. They provide enterprise infra and tooling to support today’s most widely used onchain products.

Together with Alchemy, Open House is helping businesses shape the broader programmable economy on the Arbitrum Platform.
➡️ Check out the Announcement & Register Now

Arbitrum Mentorship Program Cohort 1 Project Spotlights

The 1st Cohort of the Arbitrum Mentorship Program is underway. Selected from over 900 applicants, 13 early-stage teams across AI, payments, RWAs, and emerging DeFi are receiving 8 weeks of hands-on technical, product, and go-to-market support to launch on the Arbitrum Platform.

Check out the first few spotlights below:
➡️ Carbon
➡️ Prism
➡️ T3tris
➡️ Bond Credit

📚 Learn & Build

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

Shipping x402 on AWS and Arbitrum

Shipping agentic payments onchain just got easier. The programmable economy is already built for that. @hummusonrails breaks down exactly how: CloudFront, Lambda@Edge, CDK with AWS - all settling on the Arbitrum Platform.
➡️ Read More in the Article

StylusPort - The Faster Path from Solana to Arbitrum for Builders

Moving from Solana to the EVM means rebuilding your app from scratch.

Oak Security built StylusPort, a structured workflow for translating Solana programs into Stylus contracts, enables teams to bring Rust smart contracts to the Arbitrum Platform without starting over - faster launches, lower costs, and an easier path into the programmable economy.
➡️ Read more in the Article

B3OS is Live - The Onchain Engine for Agentic AI

Integrated with ZeroDev, the leading smart account infrastructure and development platform, B3OS enables users to architect the onchain economy of Arbitrum by combining ZeroDev’s smart accounts with gas sponsorship and session keys, and B3OS’s automation engine.

Offering 20+ ready-made templates plus a visual builder called Caddie, B3OS makes it easy for anyone to create, monitor, and connect complex, onchain workflows.
➡️ Check out the Announcement and Demo

🔦 Ecosystem Highlights

Fresh launches and standout threads from around the Arbitrum ecosystem.

Welcome Offchain Offchain Labs

Previously known as Offchain Labs, Offchain will now embark on a new chapter foccusing on powering institutions as they move onchain. Over the years, what they've built across Arbitrum, Prysm Ethereum Client, & ZeroDev are now coming together into something bigger.
➡️ Read more about the Rebrand

🛠️ Dev Tooling & Infra

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

Arbitrum Nitro version 3.9.9 Upgrade

A new Arbitrum Nitro version 3.9.9 is now available on Docker Hub with the following tag: offchainlabs/nitro-node:v3.9.9-6b0af88-stripped. This is an important release containing stability improvements and security fixes, and we recommend teams adopt it as soon as possible.
➡️ View the Official Release on GitHub

🗓️ Events

Workshops, hackathons, and ecosystem meetups to watch.

Agentic Payments & x402 Highlights at DevWorld and ETHPrague

Our DevRel Ben (@hummusonrails) recently travelled to DevWorld and ETHPrague, and gave talks on Agentic Payments with x402, how this new primitive changes the frontier of commerce, and how Arbitrum as a Platform, provides the settlement layer for it all.
➡️ Check out his Recap

🧵 Forum & Community Discussions

What builders are debating and proposing this week.

Oversight and Transparency Committee (OAT) - June 2026 Elections

The Arbitrum DAO is officially opening applications for the Oversight and Transparency Committee. The OAT serves as a vital bridge between delegates and OpCo, ensuring transparency, fiscal accountability, and strategic alignment across the ecosystem.
➡️ Read the Full Election Overview

[Technical Contribution] Resolving Stylus SDK 0.6.0

One developer has identified and documented a critical fix for developers building with the Stylus SDK (v0.6.0). The contribution addresses WASM evaluation panics caused by dependency conflicts in standard cryptographic libraries. Relevant for builders who are building with Stylus.
➡️ Read the Full Discussion

That’s all from Builder’s Block #017. Thank you for reading, and keep building. Arbitrum Everywhere.