Chinese Startup StepFun Launches a Phone Built Around an AI Agent, Not Apps

Instead of opening a ride-hailing app, typing an address and picking a car, you tell the phone where you want to go, and its agent—software that takes a goal and carries it out on its own—handles the remaining steps.

StepFun told the launch audience that in the agent era AI is no longer an add-on to a smartphone but the product itself.

StepFun first showed the agent, the operating system, and the STEPX brand in Shanghai on July 13, without a price or sales date. The company said at the time that conventional smartphone software was never built for autonomous task execution.

Siri and Gemini are assistants that live inside iOS and Android. StepFun says its Step AOS 1.0 was instead built from scratch for the agent, with long-term memory, task scheduling, and security controls in the base layer. The company describes the system as a mix of Android, Linux, and real-time operating system components.

Step AOS breaks phone functions such as messaging, apps, files and settings into small blocks the agent can call directly, using Model Context Protocol, or MCP, a shared standard that lets AI programs plug into other software. Users get two entrances: the familiar app grid and a separate space for the agent.

The agent, called Amoo, keeps one memory for the user’s facts, habits, and preferences and another for what it has learned about carrying out tasks. Simple commands like setting an alarm run on a small model inside the phone, some of them offline, while harder requests that span several apps go to a larger model in the cloud. A second MiniLED screen on the back shows what Amoo is doing.

Nearly 100 companies and products, including Alipay, Tencent, Ctrip, Didi and Meituan, have signed on to Amoo, and payments, travel bookings and content creation are still completed by their own platforms. That is StepFun’s alternative to the screen-reading and simulated-click approach Doubao used.

StepFun, founded in 2023 by former Microsoft vice president Jiang Daxin, builds its own large language model, or LLM, the kind of AI system behind ChatGPT. Its flagship, Step 5 Preview, arrived in September with 600 billion parameters, the internal numbers a model adjusts while training, of which 27 billion are active at a time.

Step 5 Preview can take in up to 1 million tokens, the chunks of text AI services count and bill by, at once. The smaller Step 3.5 Flash, released earlier this year, is open-source under an Apache 2.0 license.

The 3,999-yuan price includes 12 months of the STEPX Token Plan, which provides 100 billion tokens a month, and StepFun has not said what the AI costs after the first year.