API

Gold definitionUpdated Apr 2, 2026

Definition

An API (Application Programming Interface) defines a set of rules and protocols by which different software components can communicate and interact. In ML and agent systems, APIs enable modularity, allowing LLMs to perform function calls, agents to interact with tools, and frameworks to offer standardized access for customization and evaluation.

At a glance

Executive summary

An API is a set of rules that lets different software programs talk to each other, like a menu for ordering services. In AI, it helps large language models use external tools and allows complex AI systems to be built from smaller, independent parts, making them more flexible and easier to manage.

TL;DR

APIs are like universal connectors that let different computer programs, especially AI models and agents, communicate and work together seamlessly.

Key points

Defines rules and protocols for software components to communicate and interact.
Solves the problem of enabling modularity, interoperability, and integration of diverse software components, especially for LLMs and autonomous agents to use external tools.
Used by researchers, ML engineers, developers building agentic systems, LLM applications, and evaluation frameworks.
Unlike tightly coupled, monolithic systems, APIs promote loosely coupled, distributed architectures.
Increasingly critical for LLM-powered agents to interact with the real world, tools, and other AI systems.

Use cases

LLM Tool Use: An LLM calling a weather API to get current forecasts or a search API to retrieve information.
Agentic Workflows: An AI agent using a "multi-level API-based editing" system (like APEX) to manipulate design elements in a creative application.
Automated Code Generation: A system like NEMO using APIs to interact with autonomous coding agents to generate and validate executable mathematical optimization models.
ML Model Deployment: Exposing a trained machine learning model as a REST API endpoint for other applications to consume predictions.
Multi-Agent Simulations: A standardized API (like in STAR Benchmark) allowing different AI agents to interact within a simulated environment for competitive evaluation.

Also known as

REST API, GraphQL API, SOAP API, Web API, SDK, Interface

API