# Microsoft Copilot vs OpenAI API: who uses which

On usedby, 4 companies use Microsoft Copilot and 39 use OpenAI API. 1 company uses both, including WPP. 1 of them is known through a job post (the weakest proof) on at least one side. Counts include every proof level, job-post signals included; each company keeps its proof level on each side. Latest check 2026-10-25: 42 of 43 public lines checked.

## Side by side

|  | [Microsoft Copilot](https://www.usedby.ai/tools/microsoft-copilot.md) | [OpenAI API](https://www.usedby.ai/tools/openai-api.md) |
|---|---|---|
| Public customers | 4 | 39 |
| Confirmed | 0 | 4 |
| Observed | 0 | 33 |
| Signals (job posts) | 4 | 2 |
| Top industries of customers (every proof level) | Agency & Studio (1), Data & Analytics (1), Legal & Compliance (1) | DevTools & Infrastructure (5), Artificial Intelligence (4), Marketplace (4) |
| Category | AI assistants | Foundation models & model APIs |

## Companies that use both

Every proof level counts; the proof level of each side is shown, strongest proofs first. The first public proof is not an adoption date.

| Company | Proof, Microsoft Copilot | Proof, OpenAI API | First public proof, Microsoft Copilot | First public proof, OpenAI API |
|---|---|---|---|---|
| [WPP](https://www.usedby.ai/companies/wpp.md) | Signal (job post) | Signal (job post) | Job post, September 2026 | Job post, October 2026 |

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Source: https://www.usedby.ai/compare/microsoft-copilot-vs-openai-api · How we check: https://www.usedby.ai/methodology