MEMORILLAMemory beyond the context window
An LLM’s knowledge is fixed when training ends, yet the world it serves keeps changing. Users reveal their preferences over months, new findings overturn old ones, and agents make mistakes they should not repeat. Retraining for every change is impractical, and a frozen model forgets whatever it learns as soon as the text leaves its context window.
What a question needs is rarely known in advance. A request for energy-boosting foods may hinge on an iron deficiency mentioned months earlier in unrelated words. Placing everything in context is costly and often buries what matters, while retrieval misses information that resembles the question only weakly.
MEMORILLA instead learns to read the entire collection and distill what each question needs into a few memory tokens. Four requirements guide its design.
Collection-wide access
Each query reads the whole collection, not a few passages chosen in advance.
Query-dependent recall
What memory returns depends on the question, so one collection serves many requests.
A fixed token budget
The model receives the same few memory tokens however large the collection grows.
Reusable document embeddings
Each document is encoded once, and the store grows without re-encoding the past.
How MEMORILLA works
MEMORILLA separates remembering from recalling. A frozen encoder stores each incoming document, such as a conversation or a book chapter, as an embedding. For each question, learned memory slots read the question and the entire store, and become memory tokens that the frozen LLM reads alongside it.
- 1Converse
- 2Store
- 3Ask
- 4Read memory
- 5Answer
Session 1
March 3
My doctor says I have iron-deficiency anemia.
Memory store
0 documents
The user shares a recent diagnosis.
An illustrative example. The encoders and the LLM stay frozen, and only the memory module is trained. Attention weights are illustrative, not measured.
Growing the memory is cheap. Adding a document costs one encoder pass, as with a retrieval index, and the model always receives a fixed number of memory tokens, sixteen in our supervised experiments. Only the memory module is trained, in stages that move from paraphrasing Wikipedia to general question answering and summarization to the benchmarks’ training splits.
Results
We test MEMORILLA on eight benchmarks spanning personalization, knowledge-intensive QA and long-document QA, with every method answering through the same frozen Qwen3-8B. MEMORILLA has the highest mean score (49.68) and leads on five benchmarks, while giving the model 394 times fewer document tokens than full context on average.
Results on all eight benchmarks View scores ↗
| Benchmark / metric | Full context | Best baseline | MEMORILLA |
|---|---|---|---|
| PersonaMem-v2Accuracy (SA) | 27.92 | 30.90xRAG | 44.60Best |
| PersonalizationV4Accuracy (SA) | 59.12 | 67.88MemoRAG | 66.65 |
| PubMedQAAccuracy | 67.00 | 69.00LLMLingua-2 | 59.00 |
| FactKGAccuracy | 80.43 | 80.43Full context | 84.33Best |
| NarrativeQAROUGE-L | 17.99 | 20.51MemoRAG | 19.31 |
| TriviaQAExact match | 52.60 | 56.60MemoRAG | 57.00Best |
| LaMP-4ROUGE-L | 14.21 | 16.10xRAG | 18.15Best |
| LaMP-7ROUGE-L | 43.71 | 46.84xRAG | 48.37Best |
Scores use each benchmark’s primary metric on a 0–100 scale. Higher is better. SA denotes short-answer evaluation. The reported mean combines different metrics. PersonaMem-v2 and PersonalizationV4 receive additional benchmark-specific fine-tuning.
Personalization
A good assistant knows its user without being told twice. In PersonaMem-v2 and our synthetic PersonalizationV4, preferences are rarely stated outright and lie scattered across more than a hundred past conversations. LaMP-4 and LaMP-7 ask the model to write a headline or rewrite a tweet in the user’s own style.
User
What are some suitable foods for me to boost my energy during the day?
No memory
Whole grains, bananas, and nuts provide steady energy for …
Retrieval
Complex carbohydrates like brown rice, quinoa, and oats along with …
MEMORILLA
Given your history of iron-deficiency anemia, include iron-rich foods …
The largest margin appears on PersonaMem-v2, where MEMORILLA reaches 44.60% short-answer accuracy against 30.90% for the strongest baseline, xRAG. Full context reaches only 27.92% while using 1,974 times more document tokens. On LaMP-7, MEMORILLA lifts ROUGE-L from 43.13 without memory to 48.37.
Knowledge-intensive question answering
Some claims hold only when facts connect. Verifying the FactKG claim “AIDAstella was built by a company in Papenburg” requires linking the ship to its builder and the builder to the town.
MEMORILLA verifies 84.3% of claims, ahead of the 80.4% reached with every fact in context, while using 108 times fewer document tokens. Since full context sees every fact, the gap does not come from missing facts. As claims compose more facts, RAG-50 falls from 78.7% to 51.8%, while MEMORILLA stays above 80%.
Entities in the claim
Facts composed in the claim
Long-document question answering
Long documents bury answers in thousands of tokens, often phrased unlike the question. NarrativeQA asks about entire books and screenplays, and TriviaQA pairs trivia questions with Wikipedia and web documents.
MEMORILLA reaches the best TriviaQA exact match (57.0) with 743 times fewer document tokens than full context. On NarrativeQA, it gains most over RAG-50 on “why” and “how” questions, while RAG-50 wins on “who” and “which” questions, whose answers appear verbatim in the text.
Memory for agents
Memory becomes essential when a model must learn from its own experience. In TextWorld, a frozen Qwen3-4B agent explores up to 65 rooms to complete a quest within 50 turns, while MEMORILLA condenses its growing history into eight memory tokens. Only the memory module is trained, using reinforcement learning on the reward the game provides.
Full-history prompting
Full history in context
Move 0
MEMORILLA
Full history plus 8 memory tokens
Move 0
Schematic replay of the held-out game in Figure 7. Routes are simplified and observations are paraphrased. Move numbers refer to this illustration, not measured completion times.
Without memory, the agent shuttles between the start, laundromat, studio, salon and vault and runs out of turns. With MEMORILLA, it backtracks briefly between the salon, vault, study and canteen, then reaches the playroom goal through the restroom.
Both agents read the same full history, so the comparison isolates what eight memory tokens add. On held-out games, average success rises from 18.6% to 24.2% and games completed within three attempts from 25.0% to 37.5%. Untrained memory falls below the baseline, so the gain comes from learning, not extra tokens.
- Games completed within three attempts
- Full-history prompting: 25.0%MEMORILLA: 37.5%
- Average success rate
- Full-history prompting: 18.6%MEMORILLA: 24.2%
- Episodes that end before the turn limit
- Full-history prompting: 29%MEMORILLA: 42%
Held-out games with a frozen Qwen3-4B agent. Bars share a scale from 0 to 100%.
Memory and retrieval
Learned memory complements retrieval rather than replacing it. MEMORILLA tends to win when an answer depends on how a collection fits together, while retrieval tends to win when the answer is a name it can find verbatim. On short sources such as PubMedQA, reading the text directly remains the better choice.
PV4 is PersonalizationV4 and PMv2 is PersonaMem-v2. † Counted as answered at a ROUGE-L of at least 0.20, or MEMORILLA’s median if higher.
Each method answers questions the other misses. On FactKG, 15.9% are solved by MEMORILLA alone and 10.0% by retrieval alone. The union is an oracle bound rather than a measured hybrid, but it makes combining the two a promising next step.
Future directions
We see memory as a path toward language models that keep improving after deployment, carrying what they learn across conversations, tasks and successive models. MEMORILLA is an early step in that direction.
Toward continually learning systems
- Assistants with continuity
- An assistant could grow with a person over years, keeping each user’s memory in a separate store that can stay on their device and be deleted on request.
- Experience that improves action
- Agents could carry lessons across tasks and avoid repeating mistakes. In TextWorld, learned memory already helps an agent escape loops within a game.
- Memory beyond one model
- Because the store holds only embeddings, it could extend to images, audio and video, and portable memory modules could let one store serve many models.
- Cumulative scientific reasoning
- Research systems could connect findings across papers, code and experiments, pairing learned memory for synthesis with retrieval for verifying exact claims.
Getting there requires memory that keeps fine details and improves with use. The nearest steps are pairing memory with retrieval, training encoders for compression, and testing transfer across model families.
Current limits. MEMORILLA can lose fine-grained details such as exact names. Because it writes memory directly into the LLM’s input embeddings, it requires open model weights and a memory module trained for each LLM. All experiments pair a Qwen encoder with a Qwen decoder on text alone, so transfer to other model families and modalities is untested, as are domains such as code and science beyond biomedicine. The TextWorld agent is trained and evaluated on a single game suite with episodes of at most 50 turns, so learning across environments and over long deployments remains to be shown.
Citation
@inproceedings{fallahpour2026memorilla, title = {Memorilla: Latent Semantic Memory for {LLM}s}, author = {Adibvafa Fallahpour and Parsa Idehpour and Vignesh Kothapalli and Nikita Mounier and Shirley Wu and Shayan Pardis and Jure Leskovec}, booktitle = {COLM Workshop on Context Beyond the Window: Persistent Knowledge in Language Models}, year = {2026}, url = {https://openreview.net/forum?id=VV0vvzL783}}References
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