Agent Runtime

An agent runtime is the software layer that executes an agent loop around an LLM: it assembles inputs from state/context, interprets model outputs (messages and tool calls), runs tools, updates state, and stops when a termination condition is met.

Details

The runtime is the infrastructure and orchestration layer, distinct from the agent itself (the logical entity with goals and decisions) and from an inference provider (which handles model inference only). Agent runtimes often handle orchestration concerns such as tool routing, retries, concurrency, memory/persistence, timeouts/cancellation, tool execution approval, and integration with a sandbox and observability.

As agents take on longer-running, higher-stakes work, runtimes face emerging "agentic operating system" concerns beyond basic orchestration: agent identity and permission management (authenticating agents and scoping their access), memory and context-window management across sessions, work ledgers that track future, current, and past work with attributes like required skills, acceptance criteria, SLOs, and cost constraints, and governance paths through a graph of agent capabilities and compliance requirements. An agent is more than its persona or current context - it includes the history of work it has performed. While LLMs are fungible within an agent (one model can be swapped for another), changing a model fundamentally alters the agent's behavior and must be tracked, both for auditability and to manage agent drift. Fitness functions define machine-readable health targets that the runtime can evaluate to determine whether agent actions are improving or degrading the systems they operate on.

Examples

  • A local agent runner embedded in an IDE that can edit files and run shell commands (a filesystem agent).
  • A hosted service that executes agent loops and manages tool credentials and rate limits.
  • An agent framework/runtime library that provides a state machine, tool calling, and checkpointing.

Synonyms

agent runner, agent orchestrator, agent engine