agrepl enables deterministic replay of AI agents
The new agrepl framework provides a solution for the deterministic replay of AI agent executions, addressing the non-deterministic nature of systems using large language models and external APIs.

What happened?
Researchers from arXiv have introduced agrepl, a command-line framework designed for developers. The tool enables deterministic replay of AI agent executions. This solves the problem where AI systems, combining large language models (LLMs) with external tools and APIs, are non-deterministic. agrepl works by intercepting all external interactions at the transport layer via a 'man-in-the-middle' (MITM) proxy, serialising them as structured execution traces, and then replaying them in an isolated environment without external network access.
Key facts
| Publikationsdatum | 24 juli 2026 |
|---|---|
| Verktyg | agrepl (CLI-ramverk) |
| Teknik | Man-in-the-middle (MITM) proxy |
| Huvudproblem som löses | Icke-determinism i AI-agent system |
”AI agent systems that couple large language models (LLMs) with external tools and APIs are inherently non-deterministic: LLM sampling variance, external API state, CDN infrastructure headers, and execution-environment noise collectively prevent any prior agent run from being fait”
”We present agrepl, a developer-first CLI framework for deterministic replay of agent executions.”
Why it matters
The lack of determinism has previously prevented reliable rewriting and testing of AI agent behaviour, complicating debugging and development. agrepl's method, which formally defines the agent's execution model and uses a noise-aware diff algorithm, enables developers to faithfully recreate previous runs. This means developers can isolate and analyse problems in a controlled and predictable manner.
Who is affected?
Primarily developers working with AI agent systems and large language models are affected. Companies developing and deploying AI solutions will also benefit from the tool to improve quality assurance and troubleshooting of their systems. Indirectly, users of AI systems benefit from more stable and reliable applications.
What else you should know
The framework includes a formal definition of the agent's execution model and a noise-aware diff algorithm that classifies HTTP header deviations into meaningful signals.
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