I have not seen spec first development work well in real world environments at all. The problem is that you typically don't know what you don't know upfront for most product based decisions. Going back and forth in the spec to fix problems is a huge mistake, it just leads to contradictory sets of requirements for the agent.
What does work well is using AI to generate a quick and dirty prototype ala vibecoding, and then using that as a basis to regenerate the final code. Some might say it's still spec driven development, but the spec is a working prototype.
What does work well is using AI to generate a quick and dirty prototype ala vibecoding, and then using that as a basis to regenerate the final code. Some might say it's still spec driven development, but the spec is a working prototype.