REVIEW 1 major objections 5 minor 25 references
Delegation Drives Multi-Agent Search, Not Execution
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
T0 review · glm-5.2
2026-07-09 07:10 UTC pith:VDMWPXFA
load-bearing objection Controlled capacity sweep shows delegation matters more than execution in hierarchical search agents; the asymmetry ratio is real but the sweep design inflates it somewhat. the 1 major comments →
Think Big, Search Small: Where Capacity Matters in Hierarchical Search Agents?
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The paper's central discovery is the capacity sensitivity asymmetry between delegation and execution in hierarchical search agents. Scaling the backbone (the model that decomposes questions and plans sub-queries) yields roughly four times the accuracy gain of scaling the executor (the model that retrieves and reads documents), across the same range of model scales. This asymmetry means the Pareto frontier of accuracy-versus-cost favors concentrating capacity in the backbone while keeping the executor compact. A 1.7B-parameter executor trained with targeted trajectory distillation—preserving single-search competence while injecting multi-search correction behavior—matches a frontier sub-agent
What carries the argument
The experimental design holds the answer-generation model fixed (Qwen3-32B, chosen for low parametric contamination) and varies only one of the two studied roles at a time. The delegation-capacity sweep fixes the executor at 1.7B and scales the backbone; the execution-capacity sweep fixes the backbone at a frontier model and scales the executor. The contrast between these two sweeps localizes the bottleneck. The compact executor training pipeline uses quality-filtered trajectory distillation from a stronger teacher, with a counterfactual filter that retains multi-search demonstrations only when a single-search variant of the same query fails—ensuring the student learns genuine iterative-retr
Load-bearing premise
The claim that decomposition is the bottleneck depends on the experimental design holding the answer-generation model fixed and restricting its input to only the question and sub-query reports. If the answerer were weaker, or if it had access to raw retrieved passages or reasoning traces, execution quality might become a larger bottleneck because the answerer would need to do more synthesis work from noisier evidence.
What would settle it
If a weaker answerer or one with access to raw passages were substituted, execution capacity might become the dominant factor in end-task accuracy.
If this is right
- Practitioners building multi-agent search systems should allocate their largest, most capable model to the delegation role and use a compact specialized executor, rather than instantiating all roles from one shared model.
- A 1.7B executor trained with in-framework trajectory distillation can match a frontier sub-agent at a fraction of the token cost, making hierarchical search substantially cheaper to deploy.
- The finding that off-the-shelf end-to-end search agents (like SearchR1) underperform when placed in the executor role suggests that execution-role training data must match the input distribution of atomic sub-queries, not full multi-hop questions.
- The asymmetry implies that improving a search agent's capability is more efficiently achieved by improving decomposition quality—better relational reasoning, better sub-query scoping—than by improving retrieval or reading comprehension.
Where Pith is reading between the lines
- The bottleneck attribution depends on the answerer being strong enough to synthesize correct answers from sub-query reports alone. If the answerer were weaker or had access to noisier evidence, execution quality might become a larger bottleneck, since the system would rely more on the executor to pre-filter and organize evidence.
- The asymmetry might shift on open-web search tasks (as opposed to the fixed Wikipedia corpus used here): if retrieval is noisier and documents less structured, execution quality—particularly multi-search correction and evidence extraction—could become more capacity-sensitive.
- The same factorization logic may apply to other hierarchical agent systems beyond search (e.g., coding agents, tool-use agents): if decomposition is the bottleneck there too, compact specialized executors trained via in-framework distillation could replace frontier models in those executors.
- The counterfactual filtering technique—retaining multi-step demonstrations only when the single-step variant fails—could be a general principle for distilling iterative-correction behavior without teaching spurious retries.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This paper studies how model capacity should be distributed across roles in hierarchical (multi-agent) search agents. The authors factorize the search task into three roles—delegation (task decomposition by a main agent), execution (retrieval and evidence extraction by sub-agents), and answer generation (held fixed as a confound control). Through controlled capacity sweeps on five multi-hop QA benchmarks, they find that (1) role factorization consistently outperforms a single-agent baseline, (2) scaling the delegation backbone improves EM by ~11 points whereas scaling the execution sub-agent moves EM by only ~2.6 points, identifying decomposition as the capability bottleneck, and (3) a 1.7B-parameter executor trained via quality-filtered trajectory distillation matches a frontier sub-agent in accuracy while consuming 37% fewer tokens. The experimental design is well-controlled: the answerer is held fixed, the retrieval corpus and retriever are constant, and the exclusion of instances answerable without search is a reasonable confound control.
Significance. The paper addresses a practically important question for multi-agent search system design—where to concentrate model capacity in a delegation–execution hierarchy. The role-factorized experimental instrument is clean, and the finding that execution can be aggressively downsized while delegation remains the bottleneck is actionable. The SFT pipeline for the compact executor is well-motivated by the behavioral gap analysis (Table 4: 1.7B does single-search 99.83% of the time vs. 40.31% multi-search for the teacher), and the quality-filtering design (preserving single-search competence, injecting multi-search correction with a counterfactual filter) is a concrete, falsifiable contribution. The cross-backbone generalization check (Table 5, GLM-5.1) and the Pareto frontier analysis (Figure 3) add credibility. Code is publicly available.
major comments (1)
- §3.3, Interventions 2 and 3; §4.5, Fig. 2: The central claim—that decomposition is the capability bottleneck—rests on comparing Δ_D ≈ 11 EM (Table 2, backbone varied, executor fixed at Qwen3-1.7B) against Δ_E ≈ 2.6 EM (Table 3, executor varied, backbone fixed at DeepSeek-V4-Flash). These two sweeps are measured at different operating points of the held-fixed variable: the delegation sweep holds the executor at its weakest (1.7B), while the execution sweep holds the backbone at its strongest (DeepSeek-V4-Flash). This design choice maximizes Δ_D while minimizing Δ_E, which is a classic interaction-effect problem. The two slopes are measured on different cross-sections of the (c_D, c_E) surface, and the asymmetry could be an artifact of where each cross-section is taken rather than a property of the surface itself. The paper does not acknowledge this confound or test its robustness. At a 2×
minor comments (5)
- §4.1: The LLM-as-judge uses DeepSeek-V4-Flash, which is also used as the frontier backbone and sub-agent in several experiments. This creates a potential self-preference bias in the judge scores. Consider noting this as a limitation.
- Table 1: The EM gains from single-agent to main–sub are described as '4.5 to 8.6 points' in the abstract, but the table shows gains ranging from +4.52 to +8.63. Minor rounding inconsistency.
- Figure 9 caption: The caption reads 'Delegation prompt (part 3): worked example of a multi-hop question with sequential sub-queries,' but the figure is labeled as the execution prompt (search sub-agent) in §C.2. Caption appears mismatched.
- §4.4: The text states 'Scaling from Qwen3-1.7B to Qwen3-32B moves Avg. EM by only 1.27 points (from 39.18 to 40.45),' but Table 3 shows Qwen3-32B at 40.45 EM and Qwen3-1.7B at 39.18 EM, so the difference is 1.27. However, the abstract and §4.5 cite Δ_E ≈ 2.6, which appears to include the DeepSeek-V4-Flash sub-agent (41.77 EM). Clarify which comparison defines Δ_E.
- App. D: The SFT corpus contains 2,168 records from 1,591 unique source questions. Consider reporting the single-search vs. multi-search split in the filtered corpus to verify that the multi-search correction behavior was adequately represented.
Simulated Author's Rebuttal
We thank the referee for a careful and constructive reading of our manuscript. The referee correctly identifies a genuine confound in our experimental design: the delegation and execution sweeps are measured at different operating points of the held-fixed variable, which could inflate the apparent asymmetry. We agree this is a real concern and will address it through additional experiments and revised framing in the revision.
read point-by-point responses
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Referee: §3.3, Interventions 2 and 3; §4.5, Fig. 2: The central claim—that decomposition is the capability bottleneck—rests on comparing Δ_D ≈ 11 EM (Table 2, backbone varied, executor fixed at Qwen3-1.7B) against Δ_E ≈ 2.6 EM (Table 3, executor varied, backbone fixed at DeepSeek-V4-Flash). These two sweeps are measured at different operating points of the held-fixed variable: the delegation sweep holds the executor at its weakest (1.7B), while the execution sweep holds the backbone at its strongest (DeepSeek-V4-Flash). This design choice maximizes Δ_D while minimizing Δ_E, which is a classic interaction-effect problem. The two slopes are measured on different cross-sections of the (c_D, c_E) surface, and the asymmetry could be an artifact of where each cross-section is taken rather than a property of the surface itself. The paper does not acknowledge this confound or test its robustness.
Authors: The referee raises a valid and important concern. We acknowledge that the two capacity sweeps are measured at different operating points of the held-fixed variable, and that this design could in principle amplify the apparent asymmetry between delegation and execution sensitivity. This is a genuine confound in our current experimental design, and we appreciate the referee identifying it so precisely. In the revision, we will address it in two ways. First, we will add additional cross-sections of the (c_D, c_E) surface: specifically, we will run the delegation sweep with the executor fixed at a stronger operating point (e.g., Qwen3-32B or DeepSeek-V4-Flash) and the execution sweep with the backbone fixed at a weaker operating point (e.g., Qwen3-8B or Qwen3-14B). This will test whether the asymmetry is robust to the choice of cross-section or whether it diminishes when the held-fixed variable is set at a more comparable level. Second, we will revise the manuscript to explicitly acknowledge the interaction-effect concern in §3.3 and §4.5, and we will qualify the central claim accordingly: rather than stating that decomposition is the bottleneck as an absolute property, we will frame it as holding across the operating points we test, pending the additional cross-sections. We expect the asymmetry to persist—because the case study in §4.7 provides a mechanistic explanation for why decomposition quality governs the performance ceiling regardless of executor strength—but we agree this must be demonstrated empirically rather than assumed. If the additional experiments show that the asymmetry narrows substantially at different operating points, we will revise the strength of the claim accordingly. revision: yes
Circularity Check
No circularity found; all central claims are empirical measurements on external benchmarks with disjoint train/test splits
full rationale
The paper's three principal findings are all empirical measurements on external, independently developed benchmarks (2WikiMultihopQA, HotpotQA, MuSiQue, PopQA, Bamboogle) using independently developed models (Qwen3 series, DeepSeek-V4-Flash/Pro, GLM-5.1). (1) The role-factorization gain (Table 1) is a direct A/B comparison with the same model in both conditions. (2) The capacity-sensitivity asymmetry (Δ_D ≈ 11, Δ_E ≈ 2.6) is measured from Tables 2–3; these are observed EM differences, not quantities derived from definitions or fitted parameters. The skeptic's concern about asymmetric operating points is a valid methodology critique (correctness risk), but the measurements themselves are not circular. (3) The SFT executor result (Table 5) uses quality-filtered training trajectories (EM=1 + LLM-judge acceptance) on 3,000 training queries, evaluated on a disjoint 3,869-instance test set (Appendices D, E). Filtering training data by correctness and evaluating on held-out data is standard practice, not circularity. The one self-citation (Zhao et al., 2026) provides evaluation infrastructure (benchmarks, corpus), not a load-bearing theoretical premise. No step in the derivation chain reduces to its inputs by construction.
Axiom & Free-Parameter Ledger
free parameters (3)
- T (delegation round budget) =
4
- K (execution loop budget) =
3
- SFT corpus size =
2,168 records from 1,591 unique questions
axioms (4)
- domain assumption The answer-generation module π_A (Qwen3-32B) faithfully synthesizes answers from reports without relying on parametric memory.
- domain assumption Sub-queries are self-contained atomic questions interpretable without access to the delegation context H_D.
- domain assumption The LLM-as-judge (DeepSeek-V4-Flash) provides reliable semantic correctness assessment.
- domain assumption The Wiki-fixed corpus is a complete retrieval environment for the five benchmarks.
read the original abstract
Large language model based search agents increasingly adopt multi-agent architectures in which a main agent decomposes a complex question into sub-queries and dispatches them to parallel sub-agents. However, existing systems instantiate all roles from a single model of identical scale, leaving open how model capacity should be distributed across roles. We factorize hierarchical search into three roles: a delegation role responsible for task decomposition, an execution role responsible for retrieval and evidence extraction, and an answer generation role held fixed as a confound control. We then conduct controlled capacity sweeps along the delegation and execution axes on five multi-hop QA benchmarks. The experiments yield three findings. First, role factorization consistently outperforms a single-agent baseline, improving exact match from 4.5 to 8.6 points across six model scales. Second, capacity sensitivity is asymmetric: scaling the delegation backbone improves EM by ~11 points, whereas scaling the execution sub-agent moves EM by only ~2.6 points, identifying decomposition as the capability bottleneck. Third, a 1.7B-parameter executor trained via quality-filtered trajectory distillation matches a frontier sub-agent in accuracy while consuming 37% fewer sub-agent tokens, advancing the Pareto frontier. These results suggest a concrete recipe for building hierarchical search agents: concentrate capacity at delegation and downsize execution without sacrificing accuracy. Our code is available at https://github.com/QinnanCai0115/role-factorized-search.
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