How to implement per-user AI cost limits in your app (without rebuilding it every time)

Developers using services like OpenAI or Anthropic often face challenges managing individual user costs, as there's no straightforward way to cap how much each user can incur. While organizations can set overall spend limits, these don't prevent a single user from generating unexpectedly high costs, as one developer discovered when a user ran an AI feature in a loop, racking up $400 in API costs overnight. This article outlines practical methods to implement per-user cost limits without the need for constant redevelopment, highlighting the importance of proactive cost management to avoid financial surprises.