Behind the buy: securing Rain’s onchain stack with Guardrail

At Rain, we’ve long held the view that security has to scale ahead of the business, not chase it. 

That conviction has shaped where Rain has invested our engineering efforts, both internally and through our partnerships. A security layer has to detect threats as they happen and intervene before damage is done, and it has to do so consistently across every chain Rain operates on. The teams capable of designing and running a system like that are rare, and Guardrail is one of them. 

Guardrail is the proactive, programmable security engine monitoring transactions across 30+ chains and protecting over $30 billion in assets for customers to-date. One of these customers has been Rain. Now, Rain is bringing Guardrail’s technology and team in-house to further extend real-time protection into Rain's products. 

“The product is exceptional, but the team is the real reason this matters,” Rain Co-founder Charles Yoo-Naut said. “You can't put together this kind of expertise through individual hires. Samridh has assembled one of the very few groups in the world operating at that depth, and we're fortunate to have them at Rain."

Why runtime security matters

Guardrail is unique in that it defends protocols after deployment, not just before. Most security work in the blockchain industry has focused on pre-deployment audits, which are necessary but unable to catch what happens once contracts are live, where exploits move fast and often use techniques no static review can anticipate. Guardrail closes that gap with continuous runtime monitoring and automated response. 

The platform works as a security engine at the base layer of every transaction. Guardrail’s AI model scores each sender, recipient, and smart contract in real time to evaluate signals like transaction value, volume patterns, approval anomalies, and oracle deviations, and then responds in under 100 milliseconds. When something looks wrong, configurable circuit breakers can halt activity before funds move. Attackers typically count on going undetected for hours, but Guardrail closes that window to near zero. 

Why this matters now

This work has never been more critical. AI has changed what attackers are capable of, letting them surface exploits faster and adapt their attacks in ways defenders working with manual processes cannot match. Defending a platform like Rain against that requires the kind of continuous, automated security Guardrail has spent the past few years honing.

“We built Guardrail because the biggest unprotected surface in onchain finance isn't the code itself, it's everything that happens after it ships. More than 90% of last year's $3.4B in onchain theft hit code that had already been audited,” Guardrail Founder Samridh Saluja said. “Joining Rain takes that runtime defense to a global stablecoin payments platform where it can have outsized impact.” 

What changes for Rain and its partners

By transitioning Guardrail from a vendor to an owned infrastructure layer, the enterprises who depend on Rain get a more resilient and deeply integrated service. That means runtime security scanning every transaction across all the chains Rain operates on, normalizing detection and response regardless of whether a given chain settles in milliseconds or minutes.

Ownership also compresses the time between detection and fix. When security is a vendor relationship, every iteration cycle — identifying a new attack pattern, developing a response, testing and deploying it — has to cross organizational boundaries. With Guardrail embedded inside Rain, those loops run faster and are tuned specifically for the demands of stablecoin payment flows, where the threat surface looks different than in general DeFi.

The data advantage matters too. Running Guardrail on Rain's full transaction volume gives it cross-chain context no outside vendor can accumulate. The per-contract and per-counterparty baselines sharpen with every transaction Rain processes, and that means the protection compounds as Rain scales, rather than staying static.

Rain has operated at the frontier of stablecoin payments since day one, and as that frontier expands, so does the responsibility to protect it. Bringing Guardrail in-house is the natural next step of the conviction Rain has held from the start — security has to be built into the foundation, not bolted on after the fact.

For the enterprises, neobanks, and platforms that depend on Rain, that means every transaction across every chain and every market is protected by a security layer that gets sharper over time. As Rain grows, so does Guardrail's ability to defend it.

Looking ahead

Stablecoins are already moving billions, and the bar for production-grade security is moving up with them. The enterprises building on this rail will only commit if the infrastructure underneath can defend itself in real time.

Bringing Guardrail in-house lets Rain extend that protection as the platform grows, across new chains, new partners, and new categories of stablecoin commerce. We're excited to welcome the Guardrail team and to keep building toward a payments platform where security is part of the foundation, not bolted on top.

If you're building on stablecoins and want security designed right from the start, we'd love to work with you. Please get in touch here.