Claude vs OpenAI API: who uses which
Customers, public proof and the companies that use both.
On usedby, 73 companies use Claude and 5 use OpenAI API. No company is listed with both yet. Claude leads among the DevTools & Infrastructure companies on usedby that use either tool.Latest check Oct 8, 2026: 46 of 78 public lines checked. Counts include every proof level, job-post signals included. Companies named on both have a confirmed or observed line on each side.
Who uses Claude, OpenAI API, or both
Every company with a public proof for at least one of the two tools.
71
use only Claude
0
companies use both
3
use only OpenAI API
71 companies use only Claude, 3 use only OpenAI API and 0 use both, out of the 76 companies on usedby that use at least one of them.
2 more companies are listed for both, with a job post on one side: not counted as using both.
Where it lands
Newest customers
No new customer since tracking started on October 2, 2026.
Where it lands
Newest customers
We have not started tracking changes for OpenAI API yet.
Who uses both
Companies with a confirmed or observed line on both tools.
By industry
Which tool the companies on usedby use, by industry. Shares of the companies on usedby that use Claude, OpenAI API or both: a share of the companies on usedby, not of the market.
Claude onlyBothOpenAI API only
More common with Claude
- DevTools & Infrastructure6 of the 7 DevTools & Infrastructure companies on usedby that use either tool use Claude.
- Artificial Intelligence5 of the 5 Artificial Intelligence companies on usedby that use either tool use Claude.
Source: confirmed and observed usedby lines. Job-post signals, the weakest proof level, are left out of these shares.
Side by side
Facts from our data and from each vendor's public pages. Each line says where it comes from.
Claude
OpenAI APIWhat customers report
Results as the vendor or the customer published them, with the source and the date.
Questions about Claude and OpenAI API
Which is used more, Claude or OpenAI API?
Claude has more customers on usedby: 73 against 5 for OpenAI API.
Do companies use both Claude and OpenAI API?
usedby has not found a company with a confirmed or observed line on both Claude and OpenAI API yet.
Who uses Claude?
73 companies on usedby, each with the public page that shows it. See who uses Claude.
Who uses OpenAI API?
5 companies on usedby, each with the public page that shows it. See who uses OpenAI API.
How does usedby count customers?
A company counts when a public page shows it: a vendor's customer page, a case study, a press release or a job post, most saved with a dated capture. Every line is a customer, at one of three proof levels: confirmed, observed or signal (a job post, the weakest). A company is named as using both tools when its lines on both are confirmed or observed.