Three lines of YAML that cut our customers' CI bill by a third

When you push three times in ten minutes, GitHub runs your full pipeline three times. The first two results are read by nobody. You pay for all three.

concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true

Across repositories that added this during onboarding, a median of 31% of runs were superseded before completion. That is roughly a third of the bill spent computing results that were obsolete before they finished.

The one place not to use it

Deploy workflows. There you want a queue, not a cancellation — use a fixed group name with cancel-in-progress set to false, so deploys serialise instead of racing.