February 24, 2025

How Expensify’s open-source program is powering OpenAI’s next-gen AI engineering benchmarks

The rapid rise of large language models (LLMs) has opened up exciting new possibilities for AI-driven software development. But how well can these models tackle real-world engineering tasks? That question led to the creation of SWE-Lancer—a benchmark developed by OpenAI that evaluates LLMs using actual freelance software tasks from Expensify’s open-source repository. Let’s explore how Expensify contributed to the SWE-Lancer project and what this means for the future of AI in software engineering.

January 09, 2025

How Expensify achieves extreme concurrency with NUMA balancing

If you've never heard of "NUMA", you aren't alone – it's a bit of an IYKYK topic that very few engineers encounter in their entire careers. But if you've ever worked on an extremely high core-count server, these four letters will put shivers down your spine. Here’s a deep dive into how Expensify's core hardware works – down to the chip level – with an explanation of how that enables a critical feature of our software to work. We hope you'll find it useful as you architect your own NUMA-balanced applications on your own high-density servers!

June 17, 2024

Scaling Onyx (a postmortem)

Though it seems to be firmly behind us, I wanted to quickly take a moment to apologize for some performance and reliability issues we had a couple weeks back. We understand how critical our service is to your daily operations, and we're deeply sorry for any inconvenience this may have caused. In the spirit of transparency, here are comprehensive details on what happened, how it was fixed, and how we will ensure better reliability going forward.

July 24, 2023

Incident response at global scale

If you were trying to get shit done on your expense reports around 3:30am UTC on the morning of Friday 16th June, then you would have noticed we had a site outage. We want to share the details of our Incident Response, not just to enhance our own learnings and behaviors for next time, but to spread that knowledge with our community as well.

January 08, 2018

Scaling SQLite to 4M QPS on a single server (EC2 vs Bare Metal)

Expensify has an unusual technology stack in many ways. For example, we don't use DNS internally — just configuration-managed /etc/hosts files — and it works great. Similarly, we only make limited use of AWS — instead hosting our own hardware for the web and database layer — and it works great. But most surprising of all is that we don't use MySQL or Postgres — instead using none other than SQLite — and it works great.

May 15, 2014

Building the best expense report

This month marks the sixth anniversary of Expensify. In May 2008, David Barrett got the idea of a world where expenses reports don't have to suck. With this idea in mind he rallied the troops and founded Expensify, and for six years we've been experimenting with countless ideas on how to make expense reports not suck.

May 07, 2013

We’ve added corporate card reconciliation for more banks!

Last month we announced Amex Corporate Card Reconciliation and received a huge enthusiastic response from our users. Due to the popularity of the feature and user demand, we have expanded Corporate Card Reconciliation to many more major banks.

Engineering

How Expensify’s open-source program is powering OpenAI’s next-gen AI engineering benchmarks

How Expensify achieves extreme concurrency with NUMA balancing

Scaling Onyx (a postmortem)

Incident response at global scale

Scaling SQLite to 4M QPS on a single server (EC2 vs Bare Metal)

Building the best expense report

We’ve added corporate card reconciliation for more banks!

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