ChatGPT Business, Microsoft 365 Copilot or in-house AI?
Three ways to give your staff AI. We compare where data is processed, what IT needs, how you pay and what the subscription costs over three years. Prices come from the vendors' public price lists.
In short
ChatGPT Business
An OpenAI cloud service for teams of 2 to 200 people. SSO sign-in and connectors to Microsoft 365, Google Workspace and other tools. OpenAI states that it does not train on business data by default. You pay monthly for each user.
Microsoft 365 Copilot
An AI assistant in Microsoft 365 apps such as Word, Excel and Outlook. It is bought as an add-on to a Microsoft 365 plan and processes data in the Microsoft cloud. You pay yearly for each user.
Arminius AI
A ready-made appliance that runs entirely on your premises. The language model, search and company documents stay inside your network, and staff sign in with their company account. For law firms it includes Slovak legislation and case law. You pay once.
Side by side
| ChatGPT Business | Microsoft 365 Copilot | Arminius AIready-made appliance on your premises | |
|---|---|---|---|
| Where data is processed | in the OpenAI cloud | in the Microsoft cloud | on the appliance in your company |
| Sign-in | SSO (SAML), MFA | Microsoft 365 account | company account (Active Directory) or local accounts |
| Company documents | via connectors (Microsoft 365, Google Workspace, Slack…) | documents in Microsoft 365 | NAS and shared folders, scans included |
| Slovak law and case law by effective date | not included | not included | yes, Legal module |
| Runs without the internet | no | no | yes; on request with no outside access |
| Payment | monthly per user | yearly per user, on top of a Microsoft 365 licence | one-off, no mandatory monthly fees |
| List price | €21 per user per month | from €18.20 per user per month | quoted by number of users and modules |
What a subscription costs over 3 years
A subscription is paid for as long as you use the AI. Arminius AI is a one-off investment in the appliance and software that does not grow with the number of questions. Enter the number of people and compare.
- ChatGPT Business
- €15,120 over 3 yearsstandard seat, €21 per user per month
- Microsoft 365 Copilot Business
- €13,104 over 3 yearsadd-on to Microsoft 365, €18.20 per user per month; the Microsoft 365 licence is extra
- Arminius AI
- A one-off investment based on the number of users and modules, with no mandatory monthly fees. You receive a quote by the next working day.
Subscription cost over 3 years by number of users
| ChatGPT Business | Microsoft 365 Copilot Business | |
|---|---|---|
| 10 users | €7,560 | €6,552 |
| 25 users | €18,900 | €16,380 |
| 50 users | €37,800 | €32,760 |
Prices excluding VAT from the vendors' public price lists as of 20 October 2026. They may change; current prices are on the vendors' websites: OpenAI, Microsoft. Microsoft currently offers Copilot Business at a promotional €15.60.
When each option fits
ChatGPT Business
When you want the latest public models and internet access, and you may process company data in the cloud.
Microsoft 365 Copilot
When your company works in Microsoft 365 and you want AI right inside Word, Excel and Outlook.
Arminius AI
When data must not leave the company (contracts, case files, personal data), when you do not want to pay monthly for every person, or when you need Slovak law in every version.
Questions about the comparison
Is ChatGPT Business safe for company data?
OpenAI states that it does not train on ChatGPT Business data by default and protects access with SSO and MFA. The data is, however, processed in the OpenAI cloud. If it must not leave your company, you need an AI that runs inside your network.
Do I need a Microsoft 365 licence for Copilot?
Yes. Microsoft 365 Copilot Business is bought as an add-on to a Microsoft 365 Business plan. Microsoft also offers bundles of a plan with Copilot.
Can we run Arminius AI alongside Microsoft 365?
Yes. Arminius AI runs on its own appliance and does not need Microsoft 365. Sign-in can use Active Directory or local accounts.
Why does Arminius AI not show a price on its website?
The price depends on the number of users and modules. You receive a quote with the exact amount by e-mail after a short conversation with the consultant, by the next working day at the latest.
Tell us what you work with. We'll suggest what makes sense.
The AI consultant asks a few questions and suggests a set of modules for your company. We then send you a proposal by e-mail.
The AI consultant’s answers are informational and do not constitute a binding offer.