Lexicon · II · Access
API
Also: application programming interface
The counter through which one piece of software talks to another. For AI, it is the channel your products and internal tools use to send requests to the model, on demand, billed by the token.
The analogy
A wholesaler's trade counter. No storefront, no smiling salesperson: a precise ordering protocol, volume-based billing, and the guarantee that any business can source supplies reliably. The public never sees it, yet that is where most of the flow goes through.
A concrete example
Your CRM automatically summarizes every customer call: nobody opens a chat window. The CRM sends the transcribed recording to the model over the API, receives the summary, files it in the customer record. Thousands of times a day, silently. The bill arrives at the end of the month, counted per million tokens, like an electricity bill.
What it is NOT
It is not a product you "open": there is no screen. It is not specific to AI: the entire digital economy has run on APIs for twenty years. And it is not an implementation detail: choosing between chat subscription and API is choosing who works with the model: your humans, or your systems. Two very different adoption strategies.
Often confused with
The distinction that changes the conversation.
- Chat subscription (ChatGPT, Claude…)
- A chat subscription is a finished product for a human, at a fixed price per seat. The API is a channel for your software, billed by consumption. 'We already have ChatGPT' therefore does not mean 'our systems use AI'. They are two different channels, and two different decisions.
- MCP
- An API exposes your service to developers, who write custom code to call it. MCP is a standardized socket for plugging that service directly into a model. One addresses programs, the other addresses models. And MCP often runs on top of existing APIs.