Latest Interviews

The Thermodynamics of Trading with Daniel Pontecorvo

Daniel Pontecorvo, Ron Minsky, Dan Pontecorvo, Mark Mirchandani, David Abelson

Jane Street's physical engineering team manages a complex lifecycle of data centers and offices, prioritizing microsecond-level latency constraints and evolving from traditional air cooling to high-density liquid immersion solutions for AI infrastructure. The organization deploys proprietary monitoring stacks to prevent catastrophic failures while optimizing Power Utilization Efficiency through economizer cycles and rear-door heat exchangers that handle rack densities up to 170 kW. Their human-centric workspace design leverages modular furniture and circadian lighting to sustain collaboration, supported by a hiring strategy that blends industry veterans with graduates to challenge established engineering assumptions.

The Saga of Multicore OCaml

After a nine-year development cycle, Jane Street successfully deployed Runtime 5, a multi-core garbage collector for OCaml that addresses initial performance regressions through a redesigned pacing model and a Mark Delay synchronization patch. The team resolved complex "load-bearing bugs" and floating garbage issues to achieve stable parallelism while maintaining the sequential performance required for high-frequency trading environments. Despite rejecting the ownership model of languages like Rust, Jane Street is now releasing its production-ready OxCamel branch to facilitate researcher experimentation on future parallelism tools and type-level race freedom guarantees.

Building Tools for Traders with Ian Henry

Ian Henry, Ron Minsky, Mark Mandelbaum, Mark Mirchandani, David Eastman, Brian Dorsey

Ian Henry, a Jane Street engineer who transitioned from general web development to options trading tools, leverages the firm's custom OCaml ecosystem to build high-density interfaces that eliminate mouse usage and manage complex volatility surfaces. His recent work includes creating Bauble, a live 3D graphics environment in the Janet language that demonstrates how side projects using image-based state serialization and novel macro systems can rapidly inform internal production tooling. Through this process, Henry illustrates how Jane Street bridges the gap between low-latency exchange architecture and expert user needs by prioritizing type safety, extreme information density, and a parallel software universe free from standard web protocols.

Making OCaml Safe for Performance Engineering

Mark

Jane Street's research introduces a suite of OCaml extensions featuring unboxed types and stack allocation to eliminate memory waste and garbage collection overhead in performance-critical applications. These innovations expand into a static mode system that guarantees data race freedom for parallel execution by enforcing lifetime and portability constraints without explicit annotations. Currently deployed in production for memory management features and undergoing beta testing for concurrency safety, this work aims to integrate into mainline OCaml while earning a POPL award for its formal verification of race freedom.

Finding Signal in the Noise: Machine Learning and the Markets with In Young Cho

In Young Cho, Ron Minsky

Inyoung Cho details her transition from biology to Jane Street, where she now leads machine learning initiatives that leverage thousands of GPUs and terabytes of daily market data to navigate the anti-inductive nature of financial signals. Her presentation contrasts the firm's direct client trading model, which mitigates market impact through human interaction, with modern research pipelines that prioritize data discipline over model interpretability to prevent overfitting in high-frequency environments. Looking forward, Cho outlines how Jane Street is applying deep learning and foundation models to extract signals from multimodal data while refining internal tools through structured training that balances rapid exploration with robust production systems.

How OCaml Represents Values in Memory

Nalen

This presentation details OCaml's critical distinction between immediate and boxed types, explaining how tagged integers and heap-allocated blocks with specific headers enable efficient memory layout and garbage collection. It outlines the precise bit-level encoding strategies for primitives, variants, and special types like floats and strings, while noting the runtime's ability to dynamically inspect values and its constraints on non-immediate constructor counts. The discussion concludes by affirming the current system's performance benefits and previewing future optimization efforts toward integrating unboxed types.

Horace He: Building Machine Learning Systems for a Trillion Trillion Floating Point Operations

Horace He

Meta compiler engineer Horace He analyzes the dramatic consolidation of AI infrastructure, noting that modern model training now requires massive power resources and billions in capital to achieve state-of-the-art performance. He details how the industry has transitioned from simple imperative execution to complex compiler strategies like FlexAttention and `torch.compile`, which are essential for managing the critical balance between GPU compute and memory movement. Ultimately, He argues that the primary challenge in this field is shifting focus from pure optimization to designing robust programming models that allow developers to reliably express complex performance trade-offs in large-scale distributed systems.

System Jitter and Where to Find It: A Whack-a-Mole Experience

Tudor Brindus, Harry

A technical analysis of a simulated low-latency message passing system in OCaml demonstrates that moving from a virtualized environment to bare metal hardware reduces median round-trip latency from 637 nanoseconds to 223 nanoseconds. By sequentially isolating network interrupts with `isolcpus`, disabling timer ticks via `nohz_full`, locking CPU frequencies, and optimizing speculative execution, researchers achieved a final stable median latency of 163 nanoseconds with near-zero jitter. The study concludes that while aggressive overclocking offers marginal speed gains, it introduces unacceptable risks of memory corruption, establishing deterministic bare metal configurations as the necessary standard for reliable high-frequency trading infrastructure.

Charlie Marsh: uv: An Extremely Fast Python Package Manager

Charlie Marsh

Charlie Marsh of Astral introduces UV, a Rust-based Python package manager that functions as a unified drop-in replacement for tools like pip and Poetry by combining installation, dependency resolution, and environment management into a single high-performance workflow. Since its mid-February release, the tool has achieved 16 million monthly downloads by addressing Python's complex dependency graph challenges through advanced SAT solving, Algebraic Decision Diagrams, and a zero-copy architecture that treats virtual environments as ephemeral. UV now commands over 10% of all PyPI requests, leveraging custom version parsing and cache reflinking to enable near-instant package installation and declarative dependency locking.

The Uncertain Art of Accelerating ML Models with Sylvain Gugger

Sylvain Gugger, Ron Minsky, Jeremy Howard, Mark Mandelmann, Mark Mirchandani, Francesc Campoy, Gabriel Sanchez

Former fast.ai co-author Jeremy Howard discusses his transition from mathematics education to optimizing machine learning infrastructure at Jane Street, highlighting breakthroughs in learning rate schedules and image resizing that previously secured top benchmark placements. He details the development of the Hugging Face Accelerate library, a lightweight tool designed to abstract complex hardware parallelism and eliminate boilerplate code for training across diverse GPUs and TPUs. The discussion further explores the architectural constraints of financial data, the dominance of PyTorch's iterative execution model, and Jane Street's rigorous approach to reproducibility and custom model development for high-frequency trading.

Solving Puzzles in Production with Liora Friedberg

Liora Friedberg, Ron Minsky

Jane Street's production engineers serve as the first line of defense for its trading systems, balancing active live support with long-term projects to enhance reliability and manage a broad mental model of interconnected infrastructure. Through a blame-free culture and specialized training involving incident simulations, the team rigorously analyzes high-severity events to drive system improvements while leveraging custom tools like Oculus for precise observability and alert management. Recruiting efforts identify candidates with strong debugging instincts and communication skills who can navigate the unique pressure of minimizing opportunity costs during financial disruptions.

How to Use OCaml's Coercion Operator

camels

This session explores standard OCaml's subtyping and coercion mechanisms, emphasizing how the `:>` operator enables compile-time type checks without runtime overhead or data reallocation. The discussion details value inclusion principles for polymorphic variants, recursive subtyping relations, and the specific constraints imposed by private type abbreviations to enforce invariants. While confirming that list coercions remain free at runtime, the presentation notes upcoming analysis of variant annotations and object types in future sessions.

Unfolding the Mystery of Curved-Crease Sculpture with Origami Theorists from MIT

Martin Demaine, Eric Demaine

MIT researchers Eric and Martin Demaine collaborate as origami theorists to synthesize mathematical geometry with physical sculpture, operating on the principle that fun fuels superior artistic execution. Their bidirectional workflow transforms unsolved mathematical problems into interactive artworks like the "Solve Me" sculpture, which embeds hidden research challenges within complex, visually deceptive paper designs. By creating these impossible geometries, the duo simultaneously generates new mathematical puzzles and drives future research trajectories at the frontier of known solutions.

OCaml's New Proposed "include functor" Syntax | OCaml Unboxed

Goldfirere

Jane Street is developing an "include functor" feature for the OCaml compiler that allows modules to directly include functor results based on their own preceding definitions. This innovation eliminates the need for cumbersome intermediate wrapper modules and manual reordering, streamlining the implementation of repetitive patterns like reverse array iteration. A working compiler version supporting this syntax is currently available for testing, with plans to upstream the feature to the mainstream OCaml distribution.

From the Lab to the Trading Floor: Designing for Expert Users with Erin Murphy

Erin Murphy, Ron Minsky

Erin Murphy discusses her evolution from creating data visualization portals at NASA's Jet Propulsion Laboratory to implementing formal UX processes at Jane Street, where she addresses the unique needs of technical experts requiring high information density and keyboard-driven workflows. By prioritizing functional clarity over consumer aesthetics, Murphy leads initiatives that transition complex legacy tools into web-based interfaces while leveraging informal, ad-hoc user observations to maintain design agility within a rapidly scaling engineering environment. Her approach emphasizes recruiting domain-expert designers who can partner with engineers to solve high-complexity problems, ultimately aiming to bridge the gap between graphical usability and the composability of command-line interfaces.