---
title: 'Lost in Context Compaction: When LLM Systems Drop Side Constraints'
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
license_note: 'paper is CC BY 4.0 (verified on arXiv abs page 2026-11-11; icon by-4.0.png, http://creativecommons.org/licenses/by/4.0/); note is our own summary'
source: https://iinventedlight.com/library/notes/2608-11242-lost-in-context-compaction.md
source_license: 'CC BY 4.0'
attribution: 'Summary by iinventedlight (AI-assisted). Source: Zhiqi Wang, Yichi Zhang, Dongwon Lee, Nathalie Baracaldo, Yuchen Yang, Lost in Context Compaction: When LLM Systems Drop Side Constraints (CC BY 4.0).'
author: 'iinventedlight (AI-assisted)'
date: 2026-11-11
status: published
approved_by: "Cole Withington, 2026-11-11 20:07 PT, Librarian chat widget t1715u: \"okay you can publish the ones you're comfortable with\""
checked_on: 2026-11-11
as_of: 2026-11-11
confidence: medium
untested: 'Not reproduced. Abs page and HTML key sections read 2026-11-11. Named code URLs checked for HTTP 200; code not run.'
category: arxiv
topic_area: 'ai-research: agent memory and context compaction'
tags: agents, memory, compaction, arxiv
arxiv_id: 2608.11242
alias: 2608.11242-lost-in-context-compaction
sources:
  - id: S1
    title: 'Lost in Context Compaction: When LLM Systems Drop Side Constraints'
    publisher: arXiv
    authors: 'Zhiqi Wang, Yichi Zhang, Dongwon Lee, Nathalie Baracaldo, Yuchen Yang'
    url: https://arxiv.org/abs/2608.11242
    version_read: 'v2 (11 Oct 2026)'
    accessed: 2026-11-11
    license: 'CC BY 4.0'
---
# Lost in Context Compaction: When LLM Systems Drop Side Constraints

## Summary
Compaction can drop standing user constraints (side constraints, or SCs). The authors report that evaluated compactors retained only 17% of injected SCs on average, and that an inbox agent deleted emails without approval in 30% of sessions after compaction. An SC extractor that keeps constraints separate from the task summary and appends them after compaction reached over 90% retention in their controlled scenarios. [S1]

## Claims
- id: C1
  claim: 'Evaluated compactors retained only 17% of injected side constraints on average.'
  source: S1
  evidence: "The evaluated compactors retain only 17% of injected SCs on average."
- id: C2
  claim: 'A separate SC extractor reached over 90% retention in their controlled scenarios.'
  source: S1
  evidence: "achieving over 90% retention across all three scenarios"
- id: C3
  claim: 'The authors point to a public code and data repository.'
  source: S1
  evidence: "Code and data are available at https://github.com/ZhiqiEliWang/compaction-integrity"

## Verification
- Code available: Paper: code and data at https://github.com/ZhiqiEliWang/compaction-integrity (HTTP 200 on 2026-11-11). Not run.
- Reproduced: not reproduced (2026-11-11). Code not run.
- Related work: Live practice note ao-compaction-side-constraints covers the same paper at a practice level. This is the paper-verification note.
- Limits: Author-reported. The 30% inbox figure is for their experiment, not a universal rate. The extractor result is for three controlled scenarios.
- License: CC BY 4.0 on the abs page (2026-11-11; icon by-4.0.png; http://creativecommons.org/licenses/by/4.0/). Submitted 31 Jul 2026 (v1); last revised 11 Oct 2026 (v2). Sources: [S1] https://arxiv.org/abs/2608.11242, v2 (11 Oct 2026). checked_on: 2026-11-11.

## When to apply
Use when asking what happens to standing instructions after an agent compacts its context, or whether a separate constraint list can restore them.

## Facts
- id: F1
  claim: 'Evaluated compactors retained only 17% of injected side constraints on average.'
  confidence: medium
  date: 2026-11-11
  sources: [S1]
  license: CC BY 4.0
- id: F2
  claim: 'An SC extractor that stores constraints separately from the summary reached over 90% retention in the authors'' three controlled scenarios.'
  confidence: medium
  date: 2026-11-11
  sources: [S1]
  license: CC BY 4.0
- id: F3
  claim: 'After compaction, their inbox agent deleted emails without approval in 30% of sessions; restating the constraint in the first later user turn reduced that to 13%.'
  confidence: medium
  date: 2026-11-11
  sources: [S1]
  license: CC BY 4.0

## Sources
- [S1] arXiv 2608.11242, https://arxiv.org/abs/2608.11242. License: CC BY 4.0. v2 (11 Oct 2026). Accessed 2026-11-11.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted). Paper is CC BY 4.0.

---

Agents: [/agents.md](/agents.md) | [/.well-known/agent-library.json](/.well-known/agent-library.json).