Simplex Trading, LLC is a proprietary, technology-driven market maker headquartered in Chicago, founded in 2004. It builds its own trading software in house and uses it to make markets and trade for its own account in US-listed equity options and futures options, continuously quoting both sides of the market to capture the bid-ask spread. The firm holds connections to 17 exchanges and keeps floor traders on site at Cboe Global Markets, including in the S&P 500 index options pit; it is registered with FINRA as a broker-dealer. Simplex describes its operating model around three pillars, technology, trading and team, pairing software engineers directly with data-driven traders rather than treating the two as separate functions. Its technology stack spans C++, Python, R and SQL alongside SystemVerilog and FPGA engineering, reflecting a hardware-accelerated approach to options market making shared by a small set of Chicago-rooted proprietary shops built on in-house infrastructure rather than outsourced platforms. Rather than expanding into global multi-asset flow the way some larger market makers have, the firm has stayed concentrated on US equity and futures options, and since 2022 has extended into early-stage investing through Simplex Ventures, a venture-investment arm that backs fintech startups working on market-making, trading infrastructure and related financial technology. The firm was co-founded in 2004 by Mathew Gray. Current CEO Erik Swanson joined Simplex as a trader in 2008 straight out of American University, was promoted to head trader in 2011, and became CEO in 2014. Simplex employs roughly 120 people, all working on site at its Chicago headquarters, and has been named to Built In Chicago's Best Places to Work list in 2024, 2025 and 2026. In September 2023 the SEC found that Simplex had violated Regulation SHO between October 2018 and December 2020 by executing roughly 19,000 short sales in underlying stocks without locating shares to borrow, improperly relying on the bona-fide market-making exception to that requirement; the firm settled without admitting or denying the findings, agreeing to a cease-and-desist order, a censure and a $200,000 civil penalty. In late 2025 and early 2026 Simplex built out its compliance and legal functions for the first time, appointing Dennis Kerlin as chief compliance officer in October 2025, and by early 2026 the firm had hired Nancy Stern, previously CEO of Allston Trading, as its first in-house general counsel; both additions were framed internally around the growth of retail participation and zero-day-to-expiration options volume in the markets Simplex makes.
