An agent runtime, in the classification Agent Frameworks, Runtimes, and Harnesses- oh my! proposes, is what running agents in production calls for: software providing infrastructure-level considerations rather than abstractions for building. Harrison Chase, who wrote that post, names durable execution as the main one, and puts support for streaming, Human-in-the-loop support, thread-level persistence and cross-thread persistence in the same category. LangChain’s own example is LangGraph, which Chase says was built as a production-ready agent runtime from scratch; the projects he considers closest to it are Temporal, Inngest and other durable execution engines.
Usage
The post places runtimes beneath Agent Frameworks: they are generally lower level and can power a framework, as LangChain 1.0 is built on LangGraph to take advantage of the runtime it provides. Agent Harnesses sit higher again, on top of a framework. Chase describes the boundaries as blurry — LangGraph is probably best described as both a runtime and a framework — and presents the classification as his own attempt at a definition rather than an established one.
Jimmy Song’s chapter on the Agent Harness draws the boundary the other way up. There the agent runtime is the layer above the harness: where a harness is the runtime substrate of one agent and looks after that agent’s execution quality, the agent runtime is an operating platform for many agents, responsible for multiple sessions and tenants, scheduling, persistence, governance and the control plane, and a single runtime can manage several harness instances. In the workload framing the chapter uses, the harness is the execution layer of an agent workload and the runtime is its management layer; Song describes the two as complementary, and their separation as what lets each evolve independently at its own scale.
Related Terms
- Agent Framework — the abstraction layer a runtime can power
- Agent Harness — the batteries-included layer above a framework in LangChain’s layering, and the single-agent layer beneath a runtime in Song’s
- Human-in-the-loop — one of the capabilities the post assigns to a runtime