The IT manager at an insurer receives the CASB discovery report every month. This month: 1,200 cloud services seen, 41 of them in the AI category, with ChatGPT at the top. The report says how much traffic went to each domain and from how many devices. It does not say whether that traffic belonged to the business account, whether the organisation ever decided anything about those 41, or how much AI use took place outside the office network.
A CASB never promised that, so it is not a failing. It is where governance of AI use begins.
A CASB (cloud access security broker) looks at the traffic between your organisation and cloud services and can step in there. Governance of AI use looks at the tool: which AI services are opened, what has been decided about them and whether the employee sees that decision when opening the tool. The two overlap in discovering use and then go in different directions.
What does a CASB see?
A CASB gathers its data in three ways. It reads the logs of your firewall or proxy and recognises the domains of cloud services in them. It can use an agent on managed devices, so that traffic outside the office network is included. And through an API connection to the services you have bought yourself, such as Microsoft 365 or Google Workspace, it can see which files are stored there and who they are shared with. Microsoft describes those three layers for its own CASB in the Defender for Cloud Apps documentation.
The result is a catalogue of thousands of services, each with a risk score, and a switch per service: sanctioned or not. Through a proxy a CASB can then stop uploads, limit downloads to unmanaged devices and cut a session short. It is built for all cloud use, from storage to project tools, and AI is one category within that.
That is a lot, and it is work that governance of AI use does not do. If you have to stop uploads to unknown storage services, or map all SaaS use for a supplier register, you need a CASB and not an AI register.
What does a CASB not see?
The picture stops where the proxy stops. A remote worker without an agent, a contractor on their own laptop, a phone: that traffic never lands in a log. How large that share is varies between organisations, and nobody knows precisely, because it is the part that is not measured. Why every method has a blind spot of its own is covered in our guide to finding out which AI tools employees actually use.
A traffic log sees a domain, not an account. An employee who logs in to chatgpt.com with a personal account that trains on conversations and a colleague using the business account appear as the same line in the log. That distinction accounts for a large part of the risk, and you cannot read it from the traffic.
And a CASB looks at sessions and files, not at the text someone types into a chat window. To a traffic log, a sentence containing a citizen service number sent to an AI tool is a request like any other. To reach that moment you need something that sits in the text box; that is a different layer, explained in our comparison of Purview and BeeSensible.
What does governance of AI use add?
The decision, and the moment at which that decision is visible. A CASB knows two states per service: sanctioned or not. Governance of AI use knows four, and the most interesting one is "No decision yet". That status shows which tools are in use but have not been assessed by anyone. In a CASB those tools end up in the same bucket as the tools that were deliberately unsanctioned.
The second is where the decision appears. A CASB steps in on the network, and the employee sees a blocked page or nothing at all. Governance of AI use shows the decision in the browser as soon as someone opens the tool, with the condition the organisation drafted itself, or with the approved alternative as the first button. The employee can carry on, unless the organisation has set it so that staff cannot continue to a tool that is not allowed. That keeps the use visible, because an employee who is not stopped has no reason to switch to a phone.
The third is identity. A proxy log contains a device or a user, because a CASB is built to act on a session. The governance question does not need that: "this tool was opened four hundred times this month and has no decision" is a complete answer. What that saves you under the GDPR and with the works council is covered in AI monitoring versus employee monitoring.
| CASB | Governance of AI use | |
|---|---|---|
| What it sees | Traffic to cloud services, files in connected services | Which AI tools are opened in the browser |
| Where it looks | Proxy, firewall, agent on managed devices, API connections | The browser the extension is installed in |
| Remote work without a proxy or agent | Not visible | Visible, if the extension is installed |
| Phones | Not visible | Not visible |
| Personal or business account | Cannot be told apart by domain | Cannot be told apart by domain; it is a question for the register |
| The text box | Out of reach | Out of reach for this layer; highlighting sensitive data is a separate module |
| Statuses per service | Sanctioned or not | Allowed, limited use, no decision yet, not allowed |
| Stepping in | Can block and limit sessions | Shows the decision and the alternative; does not block of its own accord, but the organisation can set it so that staff cannot continue |
| Link to a person | Device or user in the log | No user ID; only the domain, at most once a day per device |
| Scope | All cloud use | AI tools only |
Two rows stand out. Neither sees the phone. And neither can read the account type from the domain; that is a decision you record in the AI register and show when someone opens the tool.
What does this look like in practice?
A municipality has allowed Copilot and runs a CASB on the office network. The discovery report shows Copilot, ChatGPT and Perplexity. When the organisation then looks at what is opened in the browser, including by remote workers, three specialised tools appear: a transcription tool for meetings, a translation tool and a service that summarises policy memos. Two of the three are not in any register.
The CASB did nothing wrong. The three tools were mostly used at home, outside the proxy, and for the tools that did appear in the report there was no decision to compare the report against. That is not an incident. It shows that a list of domains only becomes useful once each domain has a decision next to it, and that the decision has to reach remote workers too.
