Bloomberg reported the lawsuit in an article that Malaysia’s The Star published on 11 November. The quantitative trading unit of Steve Cohen’s investment firm Point72 brought the suit. Quantitative trading is trading based on mathematical models.

Cubist Systematic Strategies sued its former research analyst Xin Jin on 9 November in state court in Stamford, Connecticut. This account draws on court documents cited by Bloomberg and sets out Cubist’s allegations, on which the court has not ruled.

Jin joined the firm in 2019. The suit says Jin was the lead research analyst in KEPL, a 14-person team specialising in statistical arbitrage, which uses statistical models to find price anomalies.

What Cubist alleges

The suit alleges that Jin used Anthropic’s Claude and OpenAI’s Codex, both available at work, to systematically review, analyse and distil the KEPL team’s research results and source code into a readily extractable format. Cubist said the material could have been used to rebuild the team’s work outside the firm’s systems. The firm also alleges that Jin moved data to personal devices and deleted the AI tool history to evade detection.

According to Cubist’s own investigation, Jin had tried to steal, and likely did steal, confidential information. Cubist describes the code as the lifeblood of its business and a secret recipe that lets it generate positive returns.

Cubist began its investigation in July after team members raised concerns about Jin’s behaviour. The suit says Jin hinted at leaving the firm. Jin also told colleagues about buying market data for personal use, spending thousands of dollars on AI-powered coding tools and considering buying a computer with a terabyte of memory.

In July Jin told human resources about considering a move to a competitor and was put on leave. Cubist fired Jin in September after Jin reported accepting a position with a competitor. The suit does not name the competitor.

Cubist is seeking damages of an undisclosed amount. It also wants the court to bar Jin from disclosing its confidential information and from competing with it. The firm wants to examine Jin’s personal devices as well, but says Jin has refused.

Jin denies the allegations

Jin’s lawyer, Rollo Baker, said Cubist’s claims are without merit. Baker said Jin looks forward to setting the record straight.

In a filing on 10 November, Jin stated having cooperated with the former employer in a proposed mediation. The disputes also include Jin’s claim to more than $30 million in investments and compensation that Jin considers owed. The filing says Jin is due to start with a new employer in June 2028. Baker did not say which company it is.