Gusto brought in Evil Martians to work on the infrastructure behind their background jobs: Sidekiq, the Redis-backed background job framework that most large Rails applications run on. At Gusto, it’s also the layer where payroll runs, documents get processed, and money actually moves.
This is the story of our engagement, and of a question: why would a company with this much engineering talent hire consultants at all?
One of the best Rails stories in the industry
Gusto’s business is booming, and so is its engineering. The product runs on one of the largest Rails monoliths anywhere. This team has shaped how the whole industry runs big Rails codebases. Gusto pioneered packs, the gradual modularization approach that splits a monolith into team-owned packages, and open-sourced the rubyatscale tooling around it, from Packwerk-based boundary enforcement to the code_ownership gem that maps every file to a team.
They give back at the ecosystem level, too. Gusto is a Rails Foundation contributing member and became the inaugural member of Ruby Central’s Ruby Alliance in May 2026, committing significant investments into the long-term health of the Ruby ecosystem.
Membership money like that funds work the whole ecosystem gets to use. The Rails Foundation commissioned Evil Martians to build Agents on Rails, the benchmark that measures how coding agents actually perform on Rails codebases: accuracy, speed, token spend, and cost.
And they ship fast. In April 2026, Gusto acquired the compliance platform Mosey and launched payroll access inside Claude and Slack within 48 hours. By May, business owners could run payroll and ask wage and overtime questions in natural language inside Claude, ChatGPT, and Slack.
Their best velocity story comes from the top. When cofounder and head of technology Eddie Kim missed a connecting flight at Heathrow, he opened Claude Code in the airport lounge and prototyped what became Gusto Cofounder, an AI teammate for small businesses.
A team of four engineers and one designer took that prototype to a tier-one launch in ten weeks, with no Figma, Jira, or specs, with progress measured entirely in pull requests.
We’re customers, too. Evil Martians Inc. runs payroll for our US employees through Gusto, myself included. Every Friday a text message arrives to say we’ve been paid, and it still makes me smile.
