A SaaS public API is the interface that lets external developers and partner systems integrate with your product programmatically. The core design decision is REST versus GraphQL. REST exposes resources at multiple URL endpoints using standard HTTP methods and is the safest default for public APIs because it is cacheable, predictable, and familiar to every developer.
SaaS product development in 2026 is five interlocking decisions: architecture, billing, compliance, AI, and team model, each with a costly alternative if made in the wrong order. This guide covers all five with specific cost ranges, comparison tables, and real delivery data from 1,300+ projects.
