Key Takeaways Spec-driven development (SDD) makes a machine-readable specification the primary artifact; code, tests, and docs are derived from it GitHub released Spec Kit in September 2025; by April 2026 it had over 90,000 stars and supported 20+ coding agents 66% of developers say their top AI frustration is code that's "almost right, but not quite" — the failure mode specs are designed to catch Birgitta Boeckeler identifies three SDD maturity levels: spec-first, spec-anchored, and spec-as-source Specs have failure modes too: Thoughtworks Radar rated SDD "Assess, not Adopt" in November 2025 and Marmelab documented a 1,300-line spec for a one-feature date display 45% of AI-generated code samples introduced OWASP Top 10 vulnerabilities across 100+ tested models ( Cloud Security Alliance, April 2026 ). 66% of developers say their top AI frustration is output that's "almost right, but not quite" ( Stack Overflow 2025 Developer Survey ). The models keep improving. The failure mode hasn't changed.…