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HFEPX · Eval paper review

How Much Heavy Lifting Can an Agent Harness Do?: Measuring the LLM's Residual Role in a Planning Agent

Sungwoo Jung, Seonil Son

Published

Apr 8, 2026

Citations

0

Trust level

Moderate

Usefulness score

65/100 (Medium)

Extraction confidence

70% (Moderate)

Derived from extracted protocol signals and abstract evidence.

Rater population

Not reported

Signals refreshed

Apr 26, 2026

Should you rely on this paper?

This paper has useful evaluation signal, but protocol completeness is partial; pair it with related papers before deciding implementation strategy.

Use this for comparison and orientation, not as your only source.

Best use

Secondary protocol comparison source

Use if you need

A secondary eval reference to pair with stronger protocol papers.

What to verify

Validate the evaluation procedure and quality controls in the full paper before operational use.

Main weakness

No major weakness surfaced.

Human feedback signal
Detected
From extracted signals
Evaluation signal
Detected
Eval setup described
Usefulness for eval research
65/100
Moderate-confidence candidate

Useful as a secondary reference; validate protocol details against neighboring papers.

Abstract

Agent harnesses -- the stateful programs that wrap a language model and decide what it sees at each step -- are now known to change end-to-end performance on a fixed model by as much as six times. That observation raises a question asked less often than it should be: once the harness is serious, how much of an agent's competence does the harness itself already carry, and how much genuinely still needs the LLM? We study this in noisy Collaborative Battleship, a partially observable planning setting with belief update, information-gathering questions, and uncertainty-aware action selection. We externalize a planning harness into four progressively richer layers -- posterior belief tracking, declarative planning, symbolic reflection, and an LLM-backed revision gate -- and report per-layer contribution under a common runtime. We report \emph{win rate} as the primary, game-level metric and \emph{F1} as a secondary, local-targeting indicator, and pre-specify \emph{heavy lifting} as the single largest positive marginal to the primary metric. Across 54 games, the declarative planning layer does most of the heavy lifting under this criterion, raising win rate from 50.0\% (Wilson 95\% CI $[37.1,62.9]$) to 74.1\% ($[61.1,83.9]$) over a belief-only harness (+24.1pp, +0.017 F1). Symbolic reflection is mechanistically real but calibration-sensitive, shifting board-level outcomes by up to $\pm0.140$ F1 without being net-positive on aggregate. LLM-backed revision activates on only 4.3\% of turns at the strictest confidence threshold and yields a small, non-monotonic change (+0.005 F1, -3.7pp win rate). The contribution is methodological: once harness layers are made externally measurable, one can ask not only how far the harness already carries the agent, but also where the LLM's role is actually residual rather than central.

What we could verify

These are the protocol signals we could actually recover from the available paper metadata. Use them to decide whether this paper is worth deeper reading.

Human Feedback Types

strong

Critique Edit

Directly usable for protocol triage.

"Agent harnesses -- the stateful programs that wrap a language model and decide what it sees at each step -- are now known to change end-to-end performance on a fixed model by as much as six times."

Evaluation Modes

strong

Automatic Metrics

Includes extracted eval setup.

"Agent harnesses -- the stateful programs that wrap a language model and decide what it sees at each step -- are now known to change end-to-end performance on a fixed model by as much as six times."

Quality Controls

missing

Not reported

No explicit QC controls found.

"Agent harnesses -- the stateful programs that wrap a language model and decide what it sees at each step -- are now known to change end-to-end performance on a fixed model by as much as six times."

Benchmarks / Datasets

missing

Not extracted

No benchmark anchors detected.

"Agent harnesses -- the stateful programs that wrap a language model and decide what it sees at each step -- are now known to change end-to-end performance on a fixed model by as much as six times."

Reported Metrics

strong

F1, Win rate

Useful for evaluation criteria comparison.

"We report \emph{win rate} as the primary, game-level metric and \emph{F1} as a secondary, local-targeting indicator, and pre-specify \emph{heavy lifting} as the single largest positive marginal to the primary metric."

Benchmarks and datasets

No benchmark or dataset names were extracted from the available abstract.

Reported metrics

f1win rate
Human feedback details
Uses human feedback
Yes
Feedback types
Critique Edit
Rater population
Not reported
Unit of annotation
Trajectory
Expertise required
General
Evaluation details
Evaluation modes
Automatic Metrics
Agentic eval
None
Quality controls
Not reported
Evidence quality
Moderate
Use this page as
Secondary protocol comparison source

Research brief

Metadata summary

Agent harnesses -- the stateful programs that wrap a language model and decide what it sees at each step -- are now known to change end-to-end performance on a fixed model by as much as six times.

Based on abstract + metadata only. Check the source paper before making high-confidence protocol decisions.

Key takeaways

  • Agent harnesses -- the stateful programs that wrap a language model and decide what it sees at each step -- are now known to change end-to-end performance on a fixed model by as much as six times.
  • That observation raises a question asked less often than it should be: once the harness is serious, how much of an agent's competence does the harness itself already carry, and how much genuinely still needs the LLM?
  • We study this in noisy Collaborative Battleship, a partially observable planning setting with belief update, information-gathering questions, and uncertainty-aware action selection.

Researcher actions

  • Compare this paper against nearby papers in the same arXiv category before using it for protocol decisions.
  • Validate inferred eval signals (Automatic metrics) against the full paper.
  • Use related-paper links to find stronger protocol-specific references.

Caveats

  • Generated from abstract + metadata only; no PDF parsing.
  • Signals below are heuristic and may miss details reported outside the abstract.

Recommended queries

Contribution summary

  • Recent LLM-based agents often place world modeling, planning, and reflection inside a single language model loop.
  • This can produce capable behavior, but it makes a basic scientific question difficult to answer: which part of the agent's competence actually comes from the LLM, and which part comes from explicit structure around it?
  • We introduce a declared reflective runtime protocol that externalizes agent state, confidence signals, guarded actions, and hypothetical transitions into inspectable runtime structure.

Why it matters for eval

  • Recent LLM-based agents often place world modeling, planning, and reflection inside a single language model loop.
  • We introduce a declared reflective runtime protocol that externalizes agent state, confidence signals, guarded actions, and hypothetical transitions into inspectable runtime structure.

Researcher checklist

  • Human feedback protocol is explicit

    Detected: Critique Edit

  • Evaluation mode is explicit

    Detected: Automatic Metrics

  • Quality control reporting appears

    No calibration/adjudication/IAA control explicitly detected.

  • Benchmark or dataset anchors are present

    No benchmark/dataset anchor extracted from abstract.

  • Metric reporting is present

    Detected: f1, win rate