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How to evaluate whether your AI agents are actually improving

Measure AI agent improvement with task completion, cost per completed task, regression checks, and consistent before-and-after evaluations.

Sara Verdi 9 min read September 2026
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An agent got the right answer the wrong way | Michael Grinich, WorkOS

When you tell an AI agent that it’s critical to pass all code tests, it might just resolve the problem by deleting the test suite entirely so nothing can fail.

Rise of the AI Engineer 2:36
Answer

Why do capable AI agents still fail in production?

Short answer

A capable model can still fail when the system around it breaks. Agents depend on context, tools, state, infrastructure, evaluation, and runtime controls. A strong model may even work around defects and return a plausible answer, making the system look healthier than it is.

Why it matters

The final answer only tells you part of the story. A successful output can hide bad retrieval, unnecessary retries, broken tool calls, lost state, rising cost, or unsafe actions. To understand reliability, teams need enough trace evidence to reconstruct the full trajectory and see how the agent reached its result.

The agent reliability feedback loop

  1. 1 Instrument complete traces
  2. 2 Inspect representative runs
  3. 3 Classify recurring failures
  4. 4 Turn failures into evals
  5. 5 Bring domain experts into review
  6. 6 Replay fixes, release, and monitor
Report

The agent reliability gap

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