Jane Street is an American quantitative trading firm founded around 1999. In 2024 its trading revenue almost doubled, to $21bn, putting it on a par with Citigroup and Morgan Stanley. The firm has fewer than 4,000 employees; Citigroup made $20bn in its markets business with 9,000. In the second quarter of 2025 Jane Street made $6.9bn in net profit with around 3,000 employees—Goldman Sachs, with 46,000 people, managed just $3.7bn in the same period. Jane Street's earnings first exploded in 2020, hitting $8.4bn in the first half of that year. The firm is betting heavily on machine learning.
Jane Street is run by a series of committees on behalf of its partners. It has no chief executive, and its management structure is largely opaque. Staff once asked interns coming to the end of their time at the firm to guess who the equity holders were; they had mixed success. The company is legendarily secretive even by the standards of an industry that prizes opacity.
In July 2025 the Securities and Exchange Board of India (SEBI) banned Jane Street from India's securities markets, accusing it of a "sinister scheme" of manipulation in the country's options market. SEBI alleged the firm traded aggressively in the stockmarket, particularly the BANKNIFTY index of bank shares, to move much larger positions in the options market—a tactic known as "marking the close". Over 21 trading days, SEBI estimated Jane Street made 48bn rupees ($560m) through the strategies. Jane Street rejected the allegations, calling its trading "bread-and-butter arbitrage" and saying SEBI's theories demonstrated "a misunderstanding of standard hedging practices".
Jane Street's entire tech system is built on OCaml, an obscure programming language developed by French academics. The firm began rewriting its core systems in OCaml in 2005. It says the language helps "maximise the productivity of each person we hire", citing features such as static typing and functional programming. In June 2025 Jane Street announced its own variant of the language, a fork called OxCaml, whose modifications make it easier to use the language for very precise, high-efficiency coding.
Jane Street is unusual in not imposing non-compete agreements on departing staff, a practice that is common among rival funds and increasingly lengthy (often two years). Its reliance on OCaml serves as a de facto retention tool: competitors such as Millennium Management recruit engineers experienced in widely used languages like C++, Go, Java and Python, leaving few outside options for OCaml specialists.
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