Who Receives the Bill When an AI Agent Goes Rogue? — A Practical Guide to Read Before Your Monthly Cost Goes from 50,000 to 2,000,000 Yen

What If an AI That Costs 50,000 Yen a Month Delivers a Bill for 2,000,000 Yen One Morning?

This is not a hypothetical scenario.

In early 2025, an incident was reported where an AI agent from OpenAI continued to send a massive number of requests to an online database, effectively causing a DDoS attack. The AI simply executed its instructions “faithfully.” However, that “faithfulness” brought down servers and caused damage to the target.

Consider this: What if this was the AI agent of your company?

Who would receive the bill? The answer is simple. It would come to your company. An AI does not have legal personality. The contracting party is you.

For small and medium-sized enterprises (SMEs), AI agents are revolutionary tools that can handle operations worth 400,000 yen a month for just 50,000 yen. This is why their adoption is accelerating. However, behind the dramatically reduced costs lies another risk. Because it’s cheap, it can be operated casually. Because it can be operated casually, no one is watching when it goes rogue.

In this article, we will specifically estimate how much cost can arise from an AI agent going rogue and present “defensive measures that SMEs can implement starting today.”

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Three Costs That Arise from Going Rogue — How Much Specifically?

1. Explosion of Cloud Billing: From 50,000 to 2,000,000 Yen Can Happen Easily

If you are running an AI agent on the cloud, going rogue — such as entering an infinite loop or making excessive requests — directly translates to usage-based billing.

Let’s consider a hypothetical example. Suppose an agent using a GPT-4o class API has a task that normally requires 100 API calls a day, but due to a loop bug, it makes 100,000 calls a day.

• Normal: 100 calls/day × 30 days = 3,000 calls/month → About 50,000 yen
• Rogue: 100,000 calls/day × 5 days (until noticed) = 500,000 calls → About 1.7 to 2 million yen

What if the rogue behavior started over the weekend? By the time you arrive at the office on Monday morning and realize it, you already have five days’ worth of bills piling up. The cloud vendor will simply say, “Please pay for what you used.” This is the scary part of usage-based billing.

Without setting limits, AWS, Azure, and GCP will bill you without a ceiling. “Not having set a limit” is like leaving your house without locking the door.

2. Damages: If There’s a Counterparty, Litigation Risks Become Real

In cases like the OpenAI incident, if an AI agent excessively accesses external services, it can cause the target’s server to go down or services to stop.

For SMEs, a common scenario might be:

• An agent that automatically integrates with a partner’s API sends the same request tens of thousands of times due to a bug in error handling.
• The partner’s system becomes overloaded and crashes.
• The partner’s business is halted for half a day, and they bill you for lost sales and recovery costs.

If the counterparty is a mid-sized e-commerce business, the sales loss from a half-day system outage could amount to several million yen. Including the costs for recovery technicians, the damage claim could range from 5 million to 20 million yen.

What happens when a sudden claim for 20 million yen arrives at an SME? It poses a crisis for business continuity.

Moreover, the troublesome part is that legally, “what the AI did” is synonymous with “what your company did.” Under current laws, the liability for the actions of an AI agent falls on the operator. “The AI did it on its own” is not a valid defense.

3. Damage to Reputation: It Doesn’t Show in Numbers, but It’s the Most Expensive

If an AI agent unintentionally sends customer data externally or crashes a partner’s system — when such incidents become known within the industry, what is lost is not just money.

The greatest asset of an SME is its “reputation.” Local networks of business partners are small. Once the story spreads that “that AI brought down our system,” the barriers to new transactions will rise sharply.

Quantifying the cost of reputational damage is difficult, but if we assume that 10% of annual sales are lost, for a company with annual sales of 100 million yen, it would result in an annual opportunity loss of 10 million yen. Moreover, this is not just a one-year issue; recovery can take 2 to 3 years.

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What Happens When You Add It All Up?

An AI implemented to save 50,000 yen a month can cause losses of several million yen in just one instance of going rogue. This is the risk-return structure of the AI agent era.

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So, What Should You Do? — Five Defensive Measures You Can Implement Starting Today

Before investing in expensive security tools, let’s first do the basics of “locking the door.” Here are five measures that SMEs can implement starting today.

1. Set Cloud Billing Limits “Right Now”

AWS, Azure, and GCP all have budget alerts and billing limit setting features. The OpenAI API also has Usage Limits.

Time to set this up: 15 minutes. By doing this, you eliminate the risk of unlimited billing.

Specifically, set the limit to three times your estimated monthly cost. If you expect 50,000 yen, set it to stop at 150,000 yen. Even if it goes rogue, the maximum you would incur is 150,000 yen. If 15 minutes of work can prevent a loss of 1.85 million yen, there’s no reason not to do it.

2. Minimize the “Scope of Action” of the Agent

The principle is to give AI agents the “minimum necessary” permissions.

• Limit the databases they can access.
• Set limits on the number of requests to external APIs.
• Generally, do not grant write or delete permissions for files.
• Prohibit direct access to the production environment and use a sandbox instead.

This is not about “not trusting AI.” It’s about the same principle as not granting all system administrator rights to a new human employee on their first day. The same applies to AI.

3. Monitor the “Cost per Execution”

Signs of going rogue first appear as anomalies in costs.

Record the number of API calls and costs for each task execution, and create a system that triggers an alert if it exceeds three times the normal value. This can be done with just a spreadsheet and API usage logs. Expensive monitoring tools are not necessary.

Example: Normally, 10 API calls per task (cost about 17 yen) → If it exceeds 30 calls, send a Slack notification. This alone can help you notice the early stages of going rogue.

4. Insert “Human Approval” into the Process

The greatest value of AI agents is their ability to operate automatically, but the greatest risk is also their ability to operate automatically.

The solution is simple. For actions above a certain amount or impact, require human approval.

• Orders over 10,000 yen → Require human approval.
• Bulk email to external parties → Require human approval.
• Bulk updates to databases → Require human approval.

There’s no need to insist on full automation. “95% automated, 5% human verification” dramatically reduces risk.

5. Review “What the AI Did” Weekly

Take 15 minutes once a week to review the action logs of the AI agent.

“Last week, how many times did the AI operate, how much did it spend, and what errors did it produce?” — Just being aware of this can help you catch signs of going rogue. If you’re not aware, you’ll only find out about it when you receive the bill at the end of the month.

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SMEs Can Stand Out Here

Large companies have security teams. They have dedicated cloud architects. They have AI governance committees.

SMEs do not have these. That’s why the only option is to “protect through systems.”

Conversely, SMEs can make decisions quickly. Once they decide, “Let’s set the billing limit today,” they can do it today. In a large company, it might take two weeks for approval.

Countermeasures against cost explosions from AI agents are not a technical issue. It’s a matter of “whether to set it or not.” Whether or not you do the 15 minutes of setup work will determine whether a risk of several million yen is eliminated or remains.

To remain on the “using side” of AI, do not let go of the reins. Start today by checking the cloud billing limits.