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Agents / Benchmarks & Evals

Improving Long Horizon AI Agent Reliability

Original: StateM: Reaching 95.3% Raw Accuracy, or a \$15 Frontier Run, on Terminal-Bench 2.1 via Harness Scaling

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Key Takeaways

  • StateM organizes execution around durable states and recoverable runbooks to prevent common agent failure modes like losing track of state or skipping procedures.
  • The approach improves DeepSeek-V4 Flash accuracy from 82.7 percent to 88.1 percent.
  • Implementation of StateM adaptation for DeepSeek-V4 Flash costs less than 38 dollars.
  • Harness scaling allows for performance improvements without the need to retrain or modify model weights.

Summary & Methodology Analysis

StateM acts as a runtime wrapper that shifts the focus from purely model-centric execution to a managed, stateful environment. By implementing harness scaling, the system improves the execution system surrounding an agent. This involves enforcing learned controls through stateful management and organizing runtime around phase-local context, checked transitions, and versioned procedural practices. This methodology transforms postmortem findings into persistent, executable preconditions that prevent the agent from repeatedly failing due to procedural errors or premature task termination.

Interactive System Flowchart

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Cross-Examination & FAQs

A deeper dive clarifying mechanics, constraints, and baseline evaluations.

Q1. What is the primary goal of StateM?

The primary goal is to improve the reliability of long-horizon AI agents by addressing failure modes like losing track of mutable state or skipping required procedures.

Q2. Does StateM require modifying model weights?

No, StateM utilizes harness scaling to improve the execution environment surrounding an agent without modifying its model weights.

Q3. What kind of tasks does this improve?

It improves complex, long-horizon tasks where agents often fail due to procedural errors or state management issues.

Q4. What benchmarks were used to test this approach?

The paper utilizes Terminal-Bench 2.1 and BusinessBench.

Q5. Which models were evaluated in the paper?

The paper includes evaluations on DeepSeek-V4 Flash, GPT-5.5 xhigh, GPT-5.6 Sol Ultra, GPT-5.6 Sol xhigh, and GPT-5.6 Luna.

Q6. What are the specific cost implications of using StateM?

The paper reports that StateM adaptation for DeepSeek-V4 Flash costs less than 38 dollars.

Q7. Are there any limitations to this method?

Yes, the effectiveness of the approach is dependent on tasks sharing a consistent execution structure.

Q8. How much did accuracy improve for the DeepSeek-V4 Flash model?

Accuracy improved from 82.7 percent to 88.1 percent.

Q9. Does the paper mention the specific latency impact of StateM?

The paper does not specify the latency impact.

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