Exo Harness

Exo Harness is an agent architecture separating trusted infrastructure from agent logic to safely evolve across runs.

Exo Harness is a minimal architecture for building agents that separates trusted infrastructure for state, resources, and security from agent-specific logic. It splits the job of storing trusted state and deciding behavior into a durable exoharness for state, event logs, secrets, artifacts, and sandboxes, and an ephemeral executor for prompts, model calls, and tool loops. This design allows agents to stop, resume, and rewind across runs without losing resources or history. Users can swap different executors or fork from prior events. It is built for developers creating long-running agents that require a stable source of truth separate from the current prompt.

Exo Harness at a glance

Best for: Software engineer
Runs on: CLI, self-hosted
Pricing: Free
Released: May 2026
Category: AI agent tool
Website: exoharness.ai

Key features

Durable event log and state management
Ephemeral and replaceable executors
Sandboxes for running tool commands
Snapshotting across turns
Stop and resume agent runs from logs
Fork or rewind from prior events
Support for custom and swapped executors

Use it for

Building long-running AI agents
Running coding-agent harnesses safely
Experimenting with self-improving agents

Alternatives to Exo Harness

HarnessRouter — One API to manage agent runtimes, sandboxes, and execution lifecycles.
Browser Harness — Agents edit their own helper scripts mid-task to improve task completion.
LongHorizon Harness — Maintains durable task state and executes reliable, verifiable workflows over many hours.
Harness2 — It recursively refines agent execution structures using parallel and sequential search.
Sandbase Harness — It keeps agent infrastructure local, secure, and fully auditable.
Harness Engineering — Improves agent output by shaping the environment with context and tools.
Harness Meta-Skill — Generates specialized agent teams and skills for Claude Code from a single prompt.
Fusion Harness — Run 2 to 5 models simultaneously against the same working directory with a single-writer invariant.
DeepSeek Harness — Builds on a plugin architecture to organize documents, analyze tables, and write code.
Durable Harness — Recovers sessions from logs after crashes and prevents duplicate tool calls.
Repository Harness — It prepares software repositories for safe coding agent integration.
Penguin Harness — It builds complete agent applications autonomously from scratch with recursive self-improvement.

All Exo Harness alternatives