Photon raised $4.5M to let developers build agents over iMessage

Photon, a startup that helps developers build AI agents running over iMessage and WhatsApp, has closed a $4.5 million seed round after signing up more than 40,000 developers and growing revenue 10x in four months.

Gradient and A* co-led the round, with participation from Vercel, HongShan, Z Fellows, Llama Ventures, Karman, and other angel investors. Vercel's participation is notable because it is also a technology partner: Photon integrates with Vercel's Eve and ChatSDK.

The funding lands amid a live debate over where consumer AI actually lives. Meta's Muse app has soared to No. 1 on app stores, testing the opposite thesis — that users want another standalone app. Photon co-founder and CEO Daniel Tian is betting developers still need infrastructure for agents that reach people through messaging services they already use every day.

A funeral with a coffin for app icons

Photon marked its developer day on September 17 in San Francisco with a staged funeral for mobile apps — in a church, with speeches, panels from Vercel, Stripe, and OpenAI, and an actual coffin for app icons.

The event was tongue-in-cheek, but Tian means the underlying claim. "Honestly, it's going to take a while, but I think, directionally, it's inevitable," he said of the shift from apps to agents.

His argument: users no longer want to install new apps. They want agents that work inside iMessage, WhatsApp, Telegram, SMS or RCS, email, voice, and other channels they already open daily.

From hackathon bot to 40,000 developers

The idea came out of Tian and co-founder Ryan Zhu's time building consumer apps as students, often at hackathons. Every new app hit the same bottleneck: discovery. An agent running inside iMessage solved it by reaching people through Apple's Messages, an app they already use.

Tian had built a bot that texted his friends back as him over iMessage. When he and Zhu open-sourced the technology on GitHub, thousands of developers adopted it. They went all in: Tian dropped out of UPenn's M&T program, and Zhu left high school, later becoming a visiting student at MIT's Media Lab. Zhu is now Photon's CTO.

The open-source version still accounts for 98% of Photon's use today.

The product

Photon sells a package of tools for building and operating agent experiences across channels: a unified API, an extensible channel framework, a command-line interface, and an observability suite.

In April, the founders launched a managed platform sold via subscription tiers. The hosted version offers 99.95% uptime and is SOC 2 Type II and HIPAA-compliant, which opens the door to healthcare agent use cases. Usage beyond 10 users requires moving from the free tier to one of three paid tiers.

The company won't share revenue figures, but it reports less than 3% churn and says messaging volume grew 5x in the last month alone. Across hosted and open-source versions, Tian estimates the technology reaches millions of end users.

Customers include Corgi Insurance; social introductions app Boardy; Gen Z dating platform Ditto; business banking platform Rho; finance AI assistant Fliptexts; and AI email client Slashy. Nous Research's Hermes agent uses Photon as its default iMessage layer, and Photon also underpins Tencent's QClaw and NanoClaw. Framework and infrastructure integrations span LangChain, Mastra, Convex, Render, Railway, and Telnyx, among others.

The next bet: agents talking to agents

Photon today focuses on agents connecting with humans. Tian sees a larger market in connecting agents to other agents.

"I think, in the future, agents will be able to find you the agent that can do the right things — so it's going to be the A-to-A communication layer," Tian said. In his example, a person planning travel with an AI assistant could have that agent pull in a flight-booking agent or a hotel-booking agent as needed.

"It's been pretty powerful to observe the whole A-to-A-to-P [agent-to-agent-to-person] space," he said.

If Tian is right that distribution has moved from app stores to message threads, Photon is positioning itself as the infrastructure layer for that shift — whether or not Muse proves standalone AI apps can still win the consumer market.