(Yicai) Oct. 15 -- Artificial intelligence startup DeepSeek has suffered one of its most serious service outages this year, with its popular chatbot and application programming interface disrupted for almost five hours during China’s peak working hours.

The incident lasted from 8.11 a.m. to 1.04 p.m. today, affecting DeepSeek's web platform and mobile app, with many users posting on social media that it had interrupted their work. 

DeepSeek had about 129 million monthly active users as of June, ranking third among China's AI-native apps, according to a first-half market report released by QuestMobile, a research firm.

DeepSeek said at 9.06 a.m. today that the root cause had been identified and repairs were underway. At 12.49 p.m., it updated the status to “repair completed, results under monitoring,” before announcing “service restored” at 1.04 p.m. The services impacted included chat functions, DeepSeek V4.1 Pro API, and DeepSeek V4.1 Flash API, according to its official service status page.

Known for its low-cost open-source AI models, the Hangzhou-based company has so far not responded to Yicai’s inquiry about the nature of the cause.

DeepSeek's official service status records show at least 10 incidents since the start of 2026, ranging from service outages to performance degradation. A previous prolonged disruption occurred on Sept. 15, when its web platform and API services were partially unavailable for about three hours.

The privately held company stormed onto the global AI stage in January last year with the release of its ChatGPT-style R1 large language model, which paired strong reasoning performance with dramatically lower running costs. Internet pioneer and Silicon Valley venture capitalist Marc Andreessen famously described it as an “AI Sputnik moment.”

DeepSeek ranks 14th among AI apps worldwide and fifth among AI websites by monthly active users, according to a report published earlier this month by Andreessen Horowitz, the VC firm co-founded by Marc Andreessen that is also known as a16z.

Editors: Tang Shihua, Emmi Laine