GlossaryFloor 2 · The Harnessthe block and its bolted-on plates: what gets added to itFloor 2 · The Harness
API
No. 040 · v2026-08FR: APIAn API is a doorway meant for software: one program asks, another answers, in an agreed format. Like a vending machine: you explain nothing to a shop assistant, you put in what it expects and you receive what it returns.
What it is not
An API is not a model, and it is not an artificial intelligence product either. It is an access point: the model reached through an API is the same one that sits behind a chat interface, except that no harness comes with it. This is the most expensive misunderstanding in companies, where people believe they are buying the capabilities observed in a consumer product when they are buying the bare brick, with no standing instructions, no memory, no documents and no guardrails. All of that remains to be built, and that is where most of the work goes.
In depth
The contract
An API is a contract between two pieces of software: a list of available operations, what must be sent for each one, what comes back in return. This contract lets the caller ignore what happens behind it, and lets the responder change its implementation without breaking existing calls. None of this belongs to artificial intelligence: the notion is as old as software, and it holds for a banking service, a road map or a model. In this glossary it appears in two places: it is through an API that a harness reaches a model, and it is often an API that a tool queries when the harness runs it.
What an API provides
What a model API provides is narrower than one imagines. You send text, you receive text, and the service keeps nothing between two calls: the continuity of the exchange, document retrieval, the format of the answers and the limits on behaviour all fall to the caller. Billing follows the same logic, by volume of text exchanged, input included, which makes every element added to the context immediately countable. This is why two products built on the same API can differ entirely: value is built in the harness, not in the access.
The three traps
The first trap is to confuse access with control. Calling a model through an API means that your data leaves your premises, which moves the question to the contract: place of processing, retention period, possible reuse for training, subprocessors. The second is dependency, because access is not an acquired right: pricing, terms of use and the availability of versions belong to the supplier, and a withdrawn version forces the revalidation of everything that rested on it. The third is quieter: an access key circulating in a team is a door that no one is watching, and it is one of the most common routes to shadow AI in a company.
Relations where the neighbours live
Check 3 questions · click your answer
Level 1 · Recognise
A company buys API access to a model. What exactly does it receive?
Level 2 · Distinguish
Your internal assistant forgets everything from one exchange to the next, while the consumer product remembers. Why?
Level 2 · Distinguish
Where does the difference between two products calling the same API play out?
Lexigraph, "API", v2026-08, https://www.lexigraph.org/en/api/, CC BY 4.0.