Does Jane Street Use C : The Surprising Reality Explained

Primary Language at Jane Street

When discussing the technology stack at Jane Street, the conversation almost always begins and ends with OCaml. Unlike many traditional Wall Street firms or high-frequency trading (HFT) shops that rely heavily on C++ for its low-level memory management and raw speed, Jane Street has famously carved a different path. OCaml is a functional programming language that emphasizes type safety, expressiveness, and performance, making it the "tool of choice" for the firm's most serious software systems.

The firm uses OCaml for nearly everything, from its core trading engines and research tools to its internal accounting systems. This choice is not merely a preference but a strategic decision. The language allows developers to write complex, high-performance code that is also easier to reason about and maintain than equivalent code written in C or C++. By leveraging a powerful type system, Jane Street can catch many potential bugs at compile-time, which is critical in an environment where a single software error can result in massive financial losses.

The Role of C and C++

While OCaml is the dominant force, the question of whether Jane Street uses C or C++ is nuanced. In the world of high-performance computing and hardware interfacing, it is nearly impossible to avoid C entirely. However, Jane Street does not use C as a primary application language. Instead, C is typically relegated to "stubs" or foreign function interfaces (FFI). These are small pieces of code that allow OCaml to communicate with the underlying operating system, specific hardware drivers, or highly optimized third-party libraries that are natively written in C.

For example, if the firm needs to interface with a specific network card or a specialized compression library like Zstandard, they may use OCaml bindings that wrap around the original C code. In these cases, the "heavy lifting" of the logic remains in OCaml, while the C layer acts as a thin bridge to the hardware. This approach allows them to maintain the safety of a functional language without sacrificing the ability to interact with the broader ecosystem of systems-level software.

Comparing OCaml and C++ Performance

A common misconception in the industry is that functional languages are inherently slower than imperative languages like C++. While C++ offers more granular control over memory layout and CPU instructions, OCaml is remarkably efficient. Jane Street has invested decades into optimizing the OCaml compiler and developing specialized libraries to ensure their systems meet the rigorous latency requirements of modern global markets.

In many HFT environments, developers writing in Java or Python often find themselves "programming like one would in C" to avoid performance bottlenecks. At Jane Street, the philosophy is different. They use OCaml’s abstractions to build "self-adjusting" computation graphs and incremental evaluation engines. These systems, such as their "Incremental" library, allow the firm to update trading positions and risk metrics in real-time as market data changes, often achieving efficiencies that would be difficult to manage manually in a language like C.

Hardware Design and Hardcaml

Interestingly, Jane Street’s commitment to functional programming extends even into the realm of hardware. While many firms use Verilog or VHDL (which are syntactically closer to C) for FPGA and ASIC design, Jane Street uses Hardcaml. This is an internal OCaml library that allows engineers to design hardware using functional programming principles. By using Hardcaml, they can write composable testbenches and reuse typed interfaces across different hardware designs.

This approach effectively replaces the need for traditional C-style hardware description languages in many parts of their workflow. It allows for a unified language environment where the software and hardware teams can share logic, types, and testing frameworks. This level of integration is rare in the financial industry and serves as a testament to how deeply the firm has moved away from the C-centric status quo.

Other Languages in the Ecosystem

Beyond OCaml and the occasional C stub, Jane Street utilizes a small handful of other languages for specific tasks. According to internal insights, their three most used languages are OCaml, VBA, and Python. Python is frequently used by researchers and data scientists for quick analysis, machine learning prototypes, and scripting, as it is the industry standard for AI and data manipulation. VBA is often used for interfacing with Excel, which remains a staple tool for traders on the desk.

Even in the realm of machine learning, where C++ is often the backbone of frameworks like PyTorch or TensorFlow, Jane Street continues to push the boundaries of what is possible within a functional paradigm. They believe that deep learning is the future of quantitative trading and are actively applying functional programming features to large-scale production codebases to support these efforts.

Technology and Market Access

The technological intensity of Jane Street’s work requires a robust infrastructure that can handle massive volumes of data. As of early 2026, the firm averages hundreds of billions of dollars in monthly trading volume across various asset classes, including fixed income, ETFs, and derivatives. Managing this scale requires more than just a fast language; it requires a cohesive "tech stack" where every layer is designed to work together.

For retail traders looking to access similar global markets, platforms like WEEX provide a streamlined interface for engaging with digital assets. While Jane Street operates at an institutional level with custom-built OCaml engines, the underlying principle remains the same: using technology to solve the puzzle of global markets. Whether it is through high-frequency execution or long-term quantitative research, the choice of programming language is a fundamental component of a firm's competitive edge.

Summary of Language Usage

To clarify the distribution of programming languages at Jane Street, the following table outlines how different languages are applied within their infrastructure as of 2026.

Language	Primary Use Case	Frequency of Use
OCaml	Core trading systems, research, and infrastructure	Very High (Primary)
Python	Data science, machine learning, and quick scripting	Moderate
VBA	Excel integration and trader-facing tools	Moderate
C / C++	Low-level stubs, hardware drivers, and FFI	Low (Specialized)
JSQL	In-house SQL-inspired query language for data	Internal Standard

The Future of Functional Trading

As we move further into 2026, the debate between functional programming and imperative languages like C++ continues. Jane Street remains the most prominent example of a firm that has successfully scaled a functional language to the very top of the financial world. Their success suggests that the safety, modularity, and composability of OCaml provide a distinct advantage over the "pointer-heavy" and often "ugly" nature of older languages like C++.

For aspiring developers and researchers, the message is clear: while C remains a foundational language for the computing world at large, it is not the only path to high-performance trading. By mastering functional concepts, engineers can build systems that are not only fast but also robust enough to handle the volatility of 2026's global markets. Jane Street’s continued reliance on OCaml proves that with the right tools and expertise, you can outpace the competition without ever needing to write a single line of traditional C++ for your core logic.