StepFun, registered as Shanghai Jieyue Xingchen Intelligence Technology Co., Ltd. (上海阶跃星辰智能科技有限公司), is a Chinese AI developer based in Shanghai. Its model line is the Step family; the fourth generation, Step 4, is the version identified in US government reporting as of September 2026. Little of the company's funding, headcount or governance is established here.
Models
Step 4 is the only model named in the sources held. The September 2026 joint advisory AA26-251A states that between late 2025 and early 2026 StepFun distilled data from Claude Opus 4.1 and 4.5, Claude Sonnet 4.5, Claude Haiku 4.5, GPT-5 Mini, GPT-5 Pro, GPT-5.1, GPT-5.1 Codex, GPT-5.1 Codex Mini and GPT-5.2 "to improve its Step 4 model's coding and agentic functions" (Joint Cybersecurity Advisory AA26-251A: China-Based AI Companies Conducting Industrial-Scale Distillation Campaigns (NSA/CISA/FBI, September 2026)). Benchmark results, parameter counts and release dates for the Step family are not established here.
Distillation attribution
StepFun is one of six China-based companies named in the joint cybersecurity advisory released September 8, 2026 by the National Security Agency, CISA and the FBI, which states that the six extracted billions of tokens from US frontier models since at least late 2024 "likely with Chinese government awareness." The advisory attributes to StepFun a specific access pattern under the first of its four techniques described as absent from MITRE ATLAS: StepFun "structured access around pools of accounts with employees running multiple concurrent sessions, implementing load distribution to prevent quota depletion," with daily budget allocations per automated agent starting at moderate levels and "scaling significantly as operations matured" (Joint Cybersecurity Advisory AA26-251A: China-Based AI Companies Conducting Industrial-Scale Distillation Campaigns (NSA/CISA/FBI, September 2026)). See Adversarial Distillation.
Unlike DeepSeek, Moonshot AI, MiniMax and Alibaba, StepFun had not previously been named in a vendor attribution held here; the advisory is the first source naming it in this connection.
Capital restrictions
On April 24, 2026 Chinese officials directed StepFun, Moonshot AI and other technology firms to reject US capital in funding rounds without prior government approval, with similar restrictions under consideration for ByteDance secondary-market trades. The direction followed the National Development and Reform Commission's block of Meta's acquisition of Manus (Source: bloomberg.com). See Manus (Butterfly Effect).
Relationships
- instance-of: Adversarial Distillation — named as an actor in the September 2026 interagency attribution.
- related: Joint Cybersecurity Advisory AA26-251A: China-Based AI Companies Conducting Industrial-Scale Distillation Campaigns (NSA/CISA/FBI, September 2026) — the advisory naming the company, its models and its access pattern.
- related: DeepSeek, Moonshot AI, MiniMax, Zhipu AI, Alibaba / Qwen Team — the other five firms named in the same advisory.
- related: US-China AI Competition: Different Races, Different Metrics — the competitive frame.