← All notes

Short answer

Periodically condense history into a summary and continue from it. ReSum does this without retraining and gained 4.5% over ReAct. ACON tunes the compression instructions from failure cases and cut peak tokens 26-54%. [S1][S2]

Practice

Review what your summaries drop by looking at failed runs, and refine the summary prompt. [S2]

Claims

• id: C1 claim: ReSum periodically condenses interaction histories. source: S1 evidence: "periodically invoking an external tool to condense interaction histories into compact summaries"
• id: C2 claim: ReSum improved 4.5% over ReAct without training. source: S1 evidence: "ReSum achieves a 4.5% improvement over ReAct in training-free settings"
• id: C3 claim: ACON refines guidelines from failure analysis. source: S2 evidence: "iteratively refines compression guidelines based on failure analysis of the agent"
• id: C4 claim: ACON reduces peak tokens 26-54%. source: S2 evidence: "reduces peak token usage by 26-54%"

Sources

• [S1] [2509.13313] ReSum: Unlocking Long-Horizon Search Intelligence via Context Summarization. arXiv. https://arxiv.org/abs/2509.13313 . License: CC0 1.0. Accessed 2026-11-04.
• [S2] [2510.00615] ACON: Optimizing Context Compression for Long-horizon LLM Agents. arXiv. https://arxiv.org/abs/2510.00615 . License: CC BY 4.0. Accessed 2026-11-04.

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

@misc{iil_note_vfsagfpy,
  author = {{iinventedlight}},
  title = {{Summarize and resume: long-horizon agents without bigger windows}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/ao-compaction-summarize-and-resume/},
  note = {Permanent ID iil:note:vfsagfpy. License: CC-BY-4.0.},
}

Markdown

Spotted a mistake? Use the MCP feedback tool or email hello@iinventedlight.com.

For language models and agents: start at /llms.txt. This page in Markdown: /library/notes/ao-compaction-summarize-and-resume.md.