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PACMS selects context for LLM agents by optimizing submodular relevance over a single pool of memory entries, conversation turns, and tool outputs.

2026-06-26 15:45 UTC pith:GLNGYMIW

load-bearing objection The paper flags a real context-management problem for LLM agents but supplies no method, function, or results to evaluate the submodular claim. the 1 major comments →

arxiv 2606.20047 v1 pith:GLNGYMIW submitted 2026-06-18 cs.IR

PACMS: Submodular Context Selection as a Pluggable Engine for LLM Agents

Manu Ghulyani , Arunabh Singh , Karan Bharadwaj , Ankit Nath , Suranjan Goswami This is my paper
classification cs.IR
keywords context selectionLLM agentssubmodular optimizationmemory managementprompt assemblytool outputsinformation retrieval
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper presents PACMS as a pluggable component that assembles prompts by choosing a subset of available context items according to their marginal contribution to answering the current query. It models the decision as submodular maximization so that the selected set stays within the token limit while covering the most useful information from all sources at once. Current practice relies on recency truncation or external retrieval that ignores the agent's internal pool, which causes agents to lose facts needed across many turns. A reader would care because the method keeps the selection step inside the agent's own prompt-assembly logic rather than requiring separate compression or retrieval stages.

Core claim

PACMS treats memory entries, conversation turns, and tool outputs as a single candidate pool to be selected from by relevance at the moment the prompt is assembled, using submodular functions to capture the diminishing returns of adding each additional item.

What carries the argument

Submodular context selection, an optimization procedure that maximizes a submodular set function defined over the pooled candidate items subject to a cardinality or token-budget constraint.

Load-bearing premise

Submodular functions can be written that reliably measure how much each context item adds to answering an arbitrary query without hand-crafted rules for that query.

What would settle it

A multi-turn agent session in which the submodular selector omits an early fact required for the correct final answer, while a recency baseline retains it and succeeds.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

  • Prompt assembly becomes query-aware instead of depending on recency or fixed summarization schedules.
  • Memory entries, turns, and tool outputs compete on equal footing inside one selection step.
  • The selector can be inserted into existing agent loops without altering their core reasoning or tool-calling logic.
  • Token budgets are allocated to items that still contribute new relevant information rather than to recent but off-topic material.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same selection step might be reused when external retrieval results are added to the pool.
  • Long-running agents could maintain accuracy over dozens of turns without periodic manual compression.
  • Different submodular functions could be swapped in to emphasize recency, diversity, or cost for particular domains.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

1 major / 0 minor

Summary. The manuscript proposes PACMS, a pluggable engine for LLM agents that treats memory entries, conversation turns, and tool outputs as a single candidate pool and selects a subset via submodular optimization by relevance at prompt-assembly time, as an alternative to recency truncation or query-blind compression methods.

Significance. If a single fixed submodular objective can be constructed that reliably captures marginal relevance across heterogeneous item types for arbitrary queries without query-specific engineering or loss of critical facts, the approach would address a practical bottleneck in long-horizon agent sessions and provide a more principled context-management primitive than current heuristics.

major comments (1)
  1. [Abstract] Abstract: the claim that a single submodular set function can score any mixed pool (memory + turns + tool outputs) by marginal gain at prompt-assembly time is load-bearing for the 'pluggable engine' contribution, yet the manuscript supplies no explicit construction of the set function, no argument that diminishing returns hold across query types and item heterogeneity, and no demonstration that the greedy optimizer preserves critical facts when the pool is mixed.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the careful reading and the substantive comment on the core claim of the work. We address the point directly below.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the claim that a single submodular set function can score any mixed pool (memory + turns + tool outputs) by marginal gain at prompt-assembly time is load-bearing for the 'pluggable engine' contribution, yet the manuscript supplies no explicit construction of the set function, no argument that diminishing returns hold across query types and item heterogeneity, and no demonstration that the greedy optimizer preserves critical facts when the pool is mixed.

    Authors: We agree that the abstract claim is load-bearing and that the current manuscript does not supply an explicit construction of the set function, a formal argument for submodularity across heterogeneous item types, or a targeted demonstration that greedy selection preserves critical facts in mixed pools. These elements are required to support the pluggable-engine framing. We will revise the manuscript to add (1) the precise mathematical definition of the submodular objective (a linear combination of query-conditioned relevance, coverage, and diversity terms applied uniformly to the candidate pool), (2) a short subsection arguing why the diminishing-returns property is expected to hold across the three item classes without query-specific re-engineering, and (3) an additional analysis in the experimental section that isolates fact-retention rates when the pool is deliberately mixed. The abstract will be updated to reference these additions. We therefore mark this as a major revision item. revision: yes

Circularity Check

0 steps flagged

No derivation chain or equations present; claims remain architectural

full rationale

The provided manuscript text (abstract plus description) contains no equations, derivations, fitted parameters, or self-citations. The central proposal—that a single submodular objective can select from a heterogeneous pool of memory, turns, and tool outputs—is stated conceptually without any reduction to prior inputs, fitted values, or author-specific uniqueness theorems. No load-bearing step reduces by construction to its own definition or to a self-citation chain. The work is therefore self-contained as an architectural suggestion; absence of mathematical content precludes any circularity finding.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Only the abstract is available; no details on free parameters, axioms, or invented entities are provided.

pith-pipeline@v0.9.1-grok · 5768 in / 987 out tokens · 27187 ms · 2026-06-26T15:45:28.226905+00:00 · methodology

0 comments
read the original abstract

Conversational and tool-using LLM agents operate over a context window that fills from several directions simultaneously. As a session proceeds, the agent accumulates user and assistant turns, entries drawn from a persistent memory store, and often largest of all, the verbatim outputs of tool calls such as file reads, search results, and API responses. Once the cumulative context exceeds the model's token budget, the framework must decide what to keep. The prevailing mechanism is recency truncation, sometimes paired with periodic summarization. This is topic-blind: a fact established early in a session is discarded simply because it is old, even when the current user query is about exactly that fact; conversely, verbose but irrelevant recent material is retained. Agents that must recall information across many turns, the defining case for memory, are precisely where recency truncation fails. Existing alternatives sit outside the agent's assembly step. Retrieval augmented generation fetches external documents into the prompt but does not arbitrate the agent's \emph{already-present} pooled context. Context-compression methods reduce token count by rewriting or pruning text, but operate query-blind and lossily. Neither treats memory entries, conversation turns, and tool outputs as a single candidate pool to be selected from by relevance at the moment the prompt is assembled.

Figures

Figures reproduced from arXiv: 2606.20047 by Ankit Nath, Arunabh Singh, Karan Bharadwaj, Manu Ghulyani, Suranjan Goswami.

Figure 1
Figure 1. Figure 1: PACMS overview. Candidates (memory, turns, tool [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Runtime architecture. The OpenClaw plugin calls [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: PACMS as the OpenClaw context engine on a real workspace session. The user added Rust to their coding environment [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗

discussion (0)

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Reference graph

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