Does passing your eval suite before launch mean an agent will stay reliable?
No. An eval suite is a snapshot: it grades the agent against the model, prompts, and tools as they existed the day you ran it. None of those stay fixed. Teams keep shipping changes to prompts and tools, and the underlying model can change on the provider’s side with no deploy on yours, so the agent you tested is not the agent running next month. A suite that passed once says nothing about what happens after the next silent model update or the next tool that changes its response format. Treating a passing eval run as a one-time certification misses this: reliability is a property of the agent over time, not a property of one version at one moment. The only way to know an agent is still reliable is to keep watching what it does in production, not to trust the score it earned before launch.