zeromem

Rust implementation of Zero-Mem (Xiao et al., arXiv:2607.29377): agent memory where every operation outside final question answering makes zero LLM calls and consumes zero tokens. Raw conversation turns are the source of record; retrieval is structured search over them, not generated summaries.

Ships as a Rust crate, a zm CLI, a Python module (PyO3), and a memory provider plugin for Hermes Agent.

How it works

Ingest indexes each turn three ways: an entity-context graph (heuristic NER, co-occurrence edges weighted per eq 4), a temporal hierarchy (turns, windows, episodes split on session change, time gap, or topic drift), and BM25 plus dense embeddings. A query builds a deterministic profile (subject, keywords, answer type, temporal cues, session boundary), routes to a primary view, runs both retrievals, fuses with min-max normalization, closes over graph bridges and local neighbors, and calibrates the evidence set. Optionally the host can calibrate the reader's answer against typed evidence candidates.

Defaults follow the paper: gamma 0.6, rho 0.6, top-5 evidence.

Persistence is a single SQLite file (turns plus embedding cache). Graph, hierarchy, and BM25 rebuild from turns on open, so the store cannot drift from the indexes.

Deviations from the paper: spaCy NER is replaced with a heuristic extractor behind a trait, BGE-M3 with bge-small-en-v1.5 through fastembed (a deterministic hash embedder is the offline fallback and what tests use). Both are swappable. multilingual-e5-small is the other built-in dense model, for non-English conversations. Only the dense view changes with it: BM25 stopwords, relative time words, and entity extraction are still English-oriented.

Build

Rust core:

just test        # offline, hash embedder
just demo        # ingest examples/dungeon-books.jsonl, run queries
cargo build --release

The fastembed feature (default) pulls onnxruntime and downloads bge-small-en-v1.5 (~130MB) on first use. --no-default-features drops both. Pick the other model with zm --model multilingual-e5-small or zeromem.ZeroMem(path, model="multilingual-e5-small"). A store opened with a different model than it was written with re-embeds every turn on open, so switching needs no migration.

CLI:

zm --db mem.db ingest turns.jsonl     # {"session_id","speaker","text","ts"}
zm --db mem.db query "What is Carrie handling at the store?"
zm --db mem.db stats

Python:

just dev         # maturin develop into .venv

import zeromem
m = zeromem.ZeroMem("mem.db")
m.ingest_turn("s1", "user", "I moved to Jersey City on February 14, 2022.", 1644796800)
m.query("When did I move?")
m.calibrate_answer("When did I move?", "June 2021", ["I moved to Jersey City on February 14, 2022."])

Hermes Agent

ln -s $(pwd)/hermes/zeromem ~/.hermes/plugins/zeromem
uv pip install --python <hermes-python> zeromem

The first run downloads the embedding model from Hugging Face into ~/.hermes/memory/zeromem-models.

Set in ~/.hermes/config.yaml:

memory:
  provider: zeromem

Options go in ~/.hermes/memory/zeromem.json, e.g. {"model": "multilingual-e5-small"} for Spanish or other non-English conversations.

The provider syncs turns in a background thread, prefetches evidence before each turn, and exposes zeromem_recall and zeromem_stats tools. Prefetch and recall skip the active session, which is already in context, so "last session" means the one before it. Verify with just pysmoke.

Claude Code

One shared store across every project, default ~/.zeromem (override with ZEROMEM_HOME). A Stop/SessionEnd hook (zm hook) parses each session's transcript incrementally and spools clean turns without ever opening the DB; a stdio MCP server (zm mcp) holds the index open for the session, drains the spool before each call, and serves zeromem_recall, zeromem_stats, and zeromem_forget_session.

cargo install --path crates/zeromem     # zm on PATH
claude plugin marketplace add ptaranat/zeromem
claude plugin install zeromem@zeromem

Without the plugin: add the two hooks to ~/.claude/settings.json (command zm hook on Stop and SessionEnd) and register the server with claude mcp add --scope user zeromem -- zm mcp. Verify with just ccsmoke.

Caveats: Claude Code gives MCP servers no session identity, so recall can echo turns from the current session (the exclude_session argument exists for hosts that know theirs). Forgetting a session that is still open in another window partially resurrects it as that session keeps talking. There is no prompt-time prefetch; recall is tool-driven.

Credits

Method from the Zero-Mem paper by Yilin Xiao, Zhehan Zhu, Yujing Zhang, Jin Chen, Zijin Hong, Luyao Zhuang, Qinggang Zhang, Shengyuan Chen, Xiaocao Ouyang, Lingfei Ren, and Xiao Huang. This is an independent clean-room implementation from the paper text; the authors' reference code was not published at the time of writing. Integration shape follows mnemosyne.

MIT licensed.