Closed Source Model
also proprietary model
An AI model you access through an API or app but cannot download or see inside.
Analogy
Like a restaurant dish you can order but never get the secret recipe for.
Why it matters
Most top models (Claude, GPT, Gemini) are closed and billed per use, so it affects cost and data-control decisions.
In practice
You use Claude via the Anthropic API without ever hosting the model yourself.