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Retriever, a framework for robot agents that run in physical time

Linfeng Zhao, a postdoctoral researcher at Stanford, built Retriever with collaborators at Northeastern. Its time-aware 'Flow' blocks wire perception, memory, reasoning and manipulation into asynchronous feedback loops. The Retriever-0 agent demonstrates long-horizon, partially observable tasks.

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Postdoctoral researcher, Stanford
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Linfeng Zhao@LinfengZhaoZLF

How should we build long-horizon manipulation systems? As coding agents become more capable, what interface should connect models to the physical world? We’ve been thinking about this since 2024.

Introducing Retriever, a programming framework for asynchronous, closed-loop robot systems, built over the past year at Stanford and Northeastern.

- Robot agents run in physical time with various feedback loops, currently lacking a good programming abstraction.
- Retriever introduces a time-aware building block, “Flow”, analogous to a PyTorch layer or a Ray Actor.
- Users connect Flows and specify when each runs and what inputs it reads. Retriever handles asynchronous execution.
- Agents are represented as directed graphs with temporal feedback loops for closed-loop, hierarchical systems, decoupling algorithm logic from execution.

We built Retriever-0 agent to demonstrate long-horizon, partially observable tasks combining perception, memory, reasoning, and manipulation.

Here's the system in action. Paper, code, and demos below.

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