GoKawiilEarlier this year, I opened Linear to find that Tuomas, our CTO, had assigned an issue to me, titled “CI costs are high.” While I was at it, he also wanted me to make CI faster.
Agents have made it exponentially faster to ship code, but validating those changes hasn’t quite kept up at the same rate. Every PR still has to pass through CI, so as development accelerates, CI becomes a bottleneck, driving up infrastructure costs and leaving developers and agents waiting longer for feedback.
In our pursuit to make CI more performant at Linear, we optimized for how long a PR waits on CI and how much runner time it consumes. Despite our test suites almost quadrupling since the start of the year, we brought pull request wait time down from more than 6 minutes to just over 5, while cutting runner time per test roughly in half.
This is test suite performance indexed to the first week of January. The white line, tracking machine time per test, spikes when we added test shards, which shorten the wait and costs more machine time, and again during checkout stalling issues
Broadly, we improved CI in four ways:
Upgraded infrastructure and tooling
Optimized the jobs that gate other work
Reduced repeated setup
Made test execution more efficient
Linear’s codebase is primarily TypeScript, but many of these optimizations apply across languages and toolchains.
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