Many reports about AI-powered Spec-Driven Development come from greenfield demos or small projects. My experience is quite different.

For the past two years, I've been supporting companies in modernizing large business applications using the AI ​​Unified Process. This involves multiple teams, legacy systems, and various departments. This presentation will show what has worked well in these projects and where we've encountered challenges.

The focus is on four key questions: How should specifications be written so that an agent delivers usable code? How much of the generated code should we actually review, and where is the effort worthwhile? What are the practical benefits of skills and MCP servers? And where have we reached the limits of this approach?

I'll provide concrete examples from ongoing projects, including those we've discarded. This will make it clearer what Spec-Driven Development can actually achieve in large legacy systems and where its limitations lie.