THE COMPANY INDEX TRACKED BLOG
Ideas, decisions, and lessons from the team.
blogs.janestreet.com (opens on the source site)LinkedIn XThe following is part of a series of posts about 2026 summer intern projects—for more, see “What the interns have wrought, special jumbo 2026 edition”
Read at the sourceThe following is part of a series of posts about 2026 summer intern projects—for more, see “What the interns have wrought, special jumbo 2026 edition”
Read at the sourceIn August, we published a puzzle that handed you the final GDS layout of a small chip and asked you to work out what it did. We supplied the physical layout, but not a netlist or internal signal names, and it was up to you to reverse-engineer the internals. This post reveals what the chip does and explores the different ways you solved it, with shout-outs to some of our favorite submissions. The submissions We received about 400 submissions from more than 30 countries, the bulk from the US, India, the UK and Australia. Entrants included high school students, researchers, working engineers and…
Read at the sourceJane Street does a lot of network maintenance over the weekends. In each maintenance, a cabinet may lose connectivity for 15 to 25 minutes. Our internal Kafka infrastructure is supposed to be resilient to these partitions, and reconnect when connectivity resumes. For several months this year, it didn’t: processes segfaulted, leaked hundreds of thousands of sockets, or crashed in a surge of half a million TCP connections.
Read at the sourceThe following is part of a series of posts about 2026 summer intern projects—for more, see “What the interns have wrought, special jumbo 2026 edition”
Read at the sourceThe following is part of a series of posts about 2026 summer intern projects—for more, see “What the interns have wrought, special jumbo 2026 edition”
Read at the sourceThe following is part of a series of posts about 2026 summer intern projects – for more, see “What the interns have wrought, special jumbo 2026 edition”
Read at the sourceThe following is part of a series of posts about 2026 summer intern projects—for more, see “What the interns have wrought, special jumbo 2026 edition”
Read at the sourceThe following is part of a series of posts about 2026 summer intern projects—for more, see “What the interns have wrought, special jumbo 2026 edition”
Read at the sourceThe following is part of a series of posts about 2026 summer intern projects—for more, see “What the interns have wrought, special jumbo 2026 edition” Strategy and Product Specialists are versatile, cross-functional contributors who drive forward firmwide initiatives. The role requires a unique combination of big-picture thinking (“why is this valuable to the business?”) and deep analytical problem-solving. Full-time SPs work across all areas of the firm: on trading desks, in infrastructure groups, and with tech teams. An SP in finance might optimize our position management infrastructure,…
Read at the sourceIt’s time again to review some of what Jane Street’s interns built over the summer, though this year we’re going to try to cover more projects and in more depth. In particular we’re including projects from teams and roles whose work has historically been hard to talk about publicly—like ML research and trading desk operations. There’s just been too much exciting work in these areas to leave them out.
Read at the sourceThe following is part of a series of posts about 2026 summer intern projects – for more, see “What the interns have wrought, special jumbo 2026 edition”
Read at the sourceLast month, we asked you to reverse engineer a chip from nothing but its layout and teased a bigger challenge. Results and our favorite writeups are coming soon. In the meantime, here’s our next challenge! This time, you’re designing the chip, and we’ll pay to fabricate our favorite designs! We’re particularly interested in projects with unique functionality, as well as those that demonstrate novel approaches to design and verification methodologies! Winners will receive a fabricated copy of their chip, mounted on a dev boards, so they can test their design in real silicon. The challenge…
Read at the sourceTL;DR: We study the scaling laws of data weighting across in-house and open-weight LMs, finding non-monotonic behavior across scales. We vary the weight assigned to sequences during training and measure how strongly the model’s loss reduction on a sequence depends on the sequence’s weight. Taken together, our results are consistent with a general trend: as models transition from small to medium scale, they transition from learning general patterns independent of data weight to learning data-specific patterns proportional to the data weights. As models then transition from medium to large…
Read at the sourceEarlier this year we published a puzzle that handed you a complete neural network and asked you to figure out what it did. The response was great, so we’ve made another one! This time, we’re going much deeper down the tech stack. For this puzzle we’ve designed a chip, but we’re only giving you the layout. A crash course in how chips get made Modern chips start life as code. A hardware designer describes a circuit in a hardware description language like Verilog, which gets synthesized into a netlist of logic gates—NANDs, NORs, XORs, flip-flops. Then electronic design automation tools place and…
Read at the sourceJane Street is known for being an OCaml shop, but for years now Python has been our second major programming language, acting as the primary tool for data analysis and (especially importantly these days) machine learning. Most of our traders and researchers think and write in Python, even as the majority of our infrastructure is written in OCaml.
Read at the sourceI’ve been telling people for the last 25 years that Jane Street as an organization was just not interested in formal methods.
Read at the sourceWe’ve always found strace useful but somewhat hard to work with. Its output is often inscrutable, it’s hard to follow subprocesses or threads, and if you want to filter syscalls you have to rerun the trace with a flag for each one. What you want in debugging is a tool for exploring, refining, etc., but strace can make this difficult.
Read at the sourceAttention is a computational primitive at the core of modern language models, allowing internal representations to reference and influence each other. It’s how these models handle sequential data in the first place.
Read at the sourceA lot of “capture-the-flag” style ML puzzles give you a black box neural net, and your job is to figure out what it does. When we were thinking of creating our own ML puzzle early last year, we wanted to do something a little different. We thought it’d be neat to give users a complete specification of the neural net, weights and all. They would then be forced to use the tools of mechanistic interpretability to reverse engineer the network—which is a situation we sometimes find ourselves facing in our own research, when trying to interpret features of complex models.
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