From Lossy to Verified: A Provenance-Aware Tiered Memory for Agents
Organizations: School of Data Science, The Chinese University of Hong Kong, Shenzhen.
Abstract
Long-horizon agents often compress interaction histories into write-time summaries. This creates a fundamental write-before-query barrier: compression decisions are made before the system knows what a future query will hinge on. As a result, summaries can cause unverifiable omissions -- decisive constraints (e.g., allergies) may be dropped, leaving the agent unable to justify an answer with traceable evidence. Retaining raw logs restores an authoritative source of truth, but grounding on raw logs by default is expensive: many queries are answerable from summaries, yet raw grounding still requires processing far longer contexts, inflating token consumption and latency. We propose TierMem, a provenance-linked framework that casts retrieval as an inference-time evidence allocation problem. TierMem uses a two-tier memory hierarchy to answer with the cheapest sufficient evidence: it queries a fast summary index by default, and a runtime sufficiency router Escalates to an immutable raw-log store only when summary evidence is insufficient. TierMem then writes back verified findings as new summary units linked to their raw sources. On LoCoMo, TierMem achieves 0.851 accuracy (vs.0.873 raw-only) while reducing input tokens by 54.1% and latency by 60.7%.
Figures & tables
| Accuracy (LLM-Judge) | UOR % | F1 | Efficiency | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| System | Multi | Temp. | Open | Single | Overall | Rate | Overall | Tok | Tok | Lat.(s) |
| Mem0 ( Chhikara et al., 2025 ) | 0.628 | 0.707 | 0.531 | 0.712 | 0.684 | 23.3 | 0.426 | 1085.9 | 8.0 | 20.32 |
| LightMem ( Fang et al., 2025 ) | 0.709 | 0.807 | 0.542 | 0.810 | 0.773 | 14.7 | 0.495 | 1159.5 | 6.9 | 27.69 |
| O-mem ( Wang et al., 2025a ) | 0.706 | 0.776 | 0.604 | 0.797 | 0.764 | 16.3 | 0.512 | 2178.1 | 544.2 | 1.16 |
| MemOS ( Li et al., 2025 ) | 0.773 | 0.639 | 0.625 | 0.804 | 0.753 | 17.1 | 0.400 | 2692.3 | 13.3 | 10.80 |
| MemR3 ( Du et al., 2025 ) | 0.812 | 0.829 | 0.729 | 0.902 | 0.860 | - | 0.586 | 4585.7 | 384.1 | 12.30 |
| Method | SS-User | SS-Asst | SS-Pref | Multi-S | Know. Upd | Temp. Reas | Overall | UOR % | Tok /Q | Tok /Q | Lat./Q |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Mem0 | 0.800 | 0.589 | 0.533 | 0.571 | 0.667 | 0.489 | 0.596 | 29.6 | 1268 | 9 | 15.2 |
| LightMem | 0.871 | 0.339 | 0.767 | 0.790 | 0.885 | 0.700 | 0.716 | 16.8 | 1160 | 7 | 7.87 |
| O-mem | 0.957 | 0.446 | 0.773 | 0.632 | 0.551 | 0.542 | 0.620 | 25.7 | 2680 | 670 | 12.3 |
| MemOS | 0.872 | 0.617 | 0.963 | 0.514 | 0.840 | 0.557 | 0.652 | 27.4 | 1682 | 206 | 2.3 |
| MemR3 | 0.929 | 0.929 | 0.600 | 0.684 | 0.769 | 0.639 | 0.742 | - | 6347 | 437 | 18.9 |
| GAM | 0.957 | 0.964 | 0.600 | 0.752 | 0.756 | 0.629 | 0.764 | - | 37850 | 1448 | 42.3 |
| Routing Classification (Mechanism) | End-to-End QA Performance (Outcome) | ||||||
| System | R-rate | Recall (Hard) | F1-Score(%) | Overall Acc. | Router Cost | Router Lat.(s) | Lat.(s) |
| Ours (Summary-only) | 0 % | - | - | 0.755 | - | - | 1.24 |
| Ours (Raw-only) | 100% | 100.0% | - | 0.873 | - | - | 17.18 |
| Ours (Zero-shot) | 20.6% | 44.7% | 38.1 | 0.806 | 901 | 1.541 | 5.41 |
| Ours (SFT) | 38.2% | 65.8% | 37.5 | 0.831 | 680 | 0.494 | 6.28 |
| Ours (SFT+GRPO) | 39.0% | 71.7% | 40.6 | 0.851 | 678 | 0.551 | 6.76 |
| Method | Acc. | R-rate | Acc.@R | Tok /Q | Lat.(s) |
|---|---|---|---|---|---|
| Raw-only | 87.3 | 100% | 87.3 | 7398 | 17.18 |
| No-Linked | 83.6 | 38.0% | 77.5 | 3832 | 6.33 |
| Linked (ours) | 85.1 | 39.0% | 81.7 | 3980 | 6.76 |
| Epoch | Overall Acc. | S-Traffic | S-Acc. | S-Correct | Tok | Lat.(s) | ADD | UPDATE |
| No-Recall write-back (no recall; only ADD or SKIP) | ||||||||
| E1 | 0.851 | 932 | 87.9% | 819 | 3,958 | 5.14 | 720 | – |
| E2 | 0.847 | 1,125 | 87.6% | 985 (+166) | 3,035 | 4.16 | 486 | – |
| E3 | 0.845 | 1,245 | 87.0% | 1,083 (+98) | 2,419 | 3.39 | 317 | – |
| Retrieve-and-Edit write-back (recall related Tier-1, then ADD/UPDATE/SKIP) | ||||||||
| E1U | 0.851 | 932 | 87.9% | 819 | 3,958 | 5.14 | 1,186 | 209 |
| User Query | Tier-1 Summary (Compressed) | Router Decision & Reasoning |
| Case 1: Mitigating Entity Loss (The “Hero” Case) | ||
| Q: “What book recommendations has Joanna given to Nate?” | Context: “…Joanna recommended Nate to find a fantasy book series … Joanna approved the specific book series Nate showed her…” ✗ Defect: The specific entity (Book Title) is lost during summarization. | Decision: Escalate (Raw Search) Router Thought: “Summaries mention Joanna recommended a series… but do not explicitly state the book titles . They are contextually related but lack specific answers.” Outcome: Retrieved raw log containing “ Little Women ”, avoiding a vague or hallucinated answer. |
| Case 2: Semantic Sufficiency (The “Saver” Case) | ||
| Q: “What important values does John want to teach his kids through adopting a rescue dog?” | Context: “…John said adopting a rescue dog… teaches John’s kids responsibility and compassion …” ✓ Sufficient: Key semantic concepts are present. | Decision: Answer (Summary Only) Router Thought: “Summaries do not explicitly state ‘values: X’, but they hint at key points… Since summaries contain the answer (responsibility and compassion), use Summary.” Outcome: Answered correctly (Accuracy preserved) while skipping 4k tokens of raw retrieval. |
| Root cause | # | % | Description |
|---|---|---|---|
| Information missing | 156 | 41.3 | Retrieved summaries contain no explicit answer evidence (compression/coverage loss). |
| Over-generalization | 109 | 28.8 | Specific answer-critical details are abstracted away (e.g., entity/value generic descriptor). |
| Reasoning failure | 43 | 11.4 | Requires multi-step reasoning but summaries do not support it. |
| Routing decision error | 20 | 5.3 | Router selects S when summaries are insufficient (false cache hit). |
| Time confusion | 11 | 2.9 | Multiple similar events/timestamps induce ambiguity. |
| Entity confusion | 6 | 1.6 | Entity references collapse to pronouns or ambiguous mentions. |
| Router outcome on the error set | Count | Rate |
|---|---|---|
| Escalate but still wrong | 240 | 55.7% |
| False cache hit | 148 | 34.3% |
| Answer with summaries and sufficient | 43 | 10.0% |
Appendix figures & tables16 assets
Supplementary material from the paper’s appendix.
Appendix
| Parameter | Value |
|---|---|
| Train type | LoRA |
| Precision | bfloat16 |
| Epochs | 5 |
| Learning rate | |
| Max sequence length | 4096 |
| Per-device train batch size | 8 |
| Parameter | Value |
|---|---|
| RLHF type | GRPO |
| Initialization | SFT adapter checkpoint |
| Precision | bfloat16 |
| Epochs | 6 |
| Context length | 2048 |
| Learning rate | 5e-6 |
| Name | Value |
|---|---|
| Correct reward ( CORRECT_REWARD ) | 1.0 |
| Wrong penalty ( WRONG_PENALTY ) | -1.5 |
| Cost of S ( COST_S ) | 0.0 |
| Cost of R ( COST_R ) | 0.1 |
| Waste penalty for unnecessary R ( WASTE_R ) | 0.4 |
| Format error penalty ( FORMAT_ERROR_PENALTY ) | -1.0 |
| Method | Route | Tok | Tok |
|---|---|---|---|
| Linked | S | 847.5 | 97.8 |
| Linked | R | 8875.1 | 724.0 |
| No-Linked | S | 847.2 | 96.8 |
| No-Linked | R | 8705.0 | 709.9 |
| Category | Count | Decomposition (actual) |
|---|---|---|
| S_correct_R_correct | 240 | 225 correct / 15 wrong |
| S_correct_R_wrong | 33 | 13 correct / 20 wrong |
| S_wrong_R_correct | 181 | 169 correct / 12 wrong |
| S_wrong_R_wrong | 86 | 14 correct / 72 wrong |
| Total matched (R set) | 540 | 421 correct / 119 wrong |
| Category | Count | Decomposition (actual) |
|---|---|---|
| S_correct_R_correct | 313 | 305 correct / 8 wrong |
| S_correct_R_wrong | 26 | 13 correct / 13 wrong |
| S_wrong_R_correct | 170 | 153 correct / 17 wrong |
| S_wrong_R_wrong | 92 | 20 correct / 72 wrong |
| Total matched (R set) | 601 | 491 correct / 110 wrong |
| Error Category | Count |
|---|---|
| S R Errors (Summary insufficient, escalation needed) | |
| Information completeness error | 26 |
| Disambiguation failure | 17 |
| Precision requirement ignored | 16 |
| Context and focus confusion | 1 |
| Other | 1 |
Agent Memory
Agent memory lets AI systems retain, update, and use facts, experiences, and skills across sessions and long-horizon tasks.
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