Eval Debt Compounding

Eval debt is the accumulated gap between what an AI agent does in production and what anyone on the agency team can actually prove it does. Like technical debt, it accrues quietly and charges interest: every untraced failure mode, every scoring rubric that lives in a Slack thread, every client demo that worked once and was never re-run. The interest payment arrives as a retainer conversation. Agencies that instrument early convert that debt into a premium line item, because "production-ready" is a claim only evidence can support. The cost curve is moving in their favor: OpenAI cut GPT-6 Sol and Luna API prices 50% versus GPT-5.6, and prompt caching now discounts up to 90% on reused prefixes, so high-volume agent pipelines are cheaper to run and cheaper to trace. Meanwhile Forrester's 2027 predictions flag compute and infrastructure constraints that will push API-dependent tool costs upward, compressing margins on AI-inclusive retainers. Tracing spend is the hedge.