API-first is an organisational decision
Treating every capability as something another system can call changes how teams work, not just how code is structured.
API-first is often presented as a technical style. In practice it is a commitment: every capability we build is reachable, documented and stable enough for someone else to depend on.
What it buys you
Integration stops being a project. Automation becomes composition. Replacing a system becomes replacing an implementation behind an interface. The next team can build on your work instead of around it.
What it costs
Designing interfaces before implementations, versioning deliberately, writing documentation as part of done. These are habits, and habits are organisational.