To prevent unexpected high costs from AI agents making excessive API calls, users can set usage limits on their OpenAI account. Usage tiers act as a safeguard: until a user has spent a total of $50 on API calls, they are locked into Tier 1, which limits spending to $100/month. After spending $50, users move to Tier 2, allowing $500/month. Spending a total of $100 reaches Tier 3, with a $1,000/month limit. Spending a total of $250 reaches Tier 4, allowing up to $5,000/month. Once a user has spent $1,000 paid to OpenAI, the limit rises to $200,000 per month. The article warns that without setting specific spending limits, an AI app could generate hundreds of thousands of dollars in charges. The spending limits page notes that "Your actual costs may exceed this based on usage," because OpenAI does not place a hard limit on spending unless configured.