fademem

Deterministic, fully local memory-decay scoring and pruning for AI-agent long-term-memory stores.

fademem gives you two composable decay models, a fixed-width C ABI for cross-language use, a Python package with native acceleration and a pure-Python fallback, and a standalone JSONL sweep CLI with safe mutation modes and structured audit logs. No hosted service, no LLM, no embeddings, no database. Everything runs in-process on your machine.

What it does

AI agents accumulate long-term memories. Not all of them stay relevant. fademem applies deterministic scoring to decide which memories to retain and which to prune, based on how recently they were accessed and how important they are. You supply the current time, the model parameters, and a threshold. The library returns a score in [0.0, 1.0] for each memory. Scores below your threshold are candidates for pruning.

Scoring models

Exponential

score = exp2(-age_ms / half_life_ms)

Time since last access decays exponentially. half_life_ms controls how fast memories fade. At one half-life, the score is 0.5. At two, 0.25. And so on.

Importance-weighted power-law

score = importance * exp(-exponent * log1p(age_ms / scale_ms))

importance (in [0, 1]) sets the initial eligibility of a memory. scale_ms controls the time horizon. exponent controls how aggressively age reduces the score. The power-law decay is slower than exponential for old memories, which better matches how agents access historical context.

Semantics

• Time values are signed Unix UTC epoch milliseconds (int64 / int64_t / Python int).
• Future timestamps clamp age_ms to zero (score stays at full importance or 1.0).
• Pruning is strict: score < threshold prunes. Equality retains. This makes behavior stable at the boundary.
• All scoring is deterministic and stateless. No clock, filesystem, environment, or network reads.

Install (Python)

The package is published on PyPI:

pip install fademem

Or build from source with uv:

cd python
uv build --wheel
pip install dist/*.whl

Quickstart

from fademem import exponential_score, power_law_score
from fademem.jsonl import scan_exponential_jsonl, archive_exponential_jsonl, delete_exponential_jsonl

# Score a single memory
score = exponential_score(
    last_accessed=1_000_000,
    now=87_400_000,
    half_life_millis=86_400_000,
)
# score == 0.5

score = power_law_score(
    last_accessed=1_000_000,
    now=87_400_000,
    scale_millis=86_400_000,
    exponent=1.0,
    importance=0.5,
)
# score == 0.25

# Scan a JSONL store (no mutation)
decisions = scan_exponential_jsonl(
    "memories.jsonl",
    now=87_400_000,
    half_life_millis=86_400_000,
    threshold=0.5,
)
for d in decisions:
    print(f"{d.id}: score={d.score:.4f} prune={d.prune}")

# Archive pruned records to a separate file
archive_exponential_jsonl(
    "memories.jsonl",
    "archive.jsonl",
    now=87_400_000,
    half_life_millis=86_400_000,
    threshold=0.5,
)

# Delete pruned records in place
delete_exponential_jsonl(
    "memories.jsonl",
    now=87_400_000,
    half_life_millis=86_400_000,
    threshold=0.5,
)

Power-law variants (scan_power_law_jsonl, archive_power_law_jsonl, delete_power_law_jsonl) accept scale_millis, exponent, and threshold instead of half_life_millis.

In-memory scoring API

For use with existing memory systems (no file I/O required):

from fademem import MemoryRecord, score_memories, prune_memories

# Score memories directly from your application
memories = [
    MemoryRecord(id="msg-1", last_accessed_ms=87_400_000, importance=0.8),
    MemoryRecord(id="msg-2", last_accessed_ms=-85_400_000, importance=0.5),
]

decisions = score_memories(
    memories,
    model="power-law",
    now=87_400_000,
    scale_millis=86_400_000,
    exponent=1.0,
    threshold=0.25,
)

for d in decisions:
    print(f"{d.id}: score={d.score:.4f} prune={d.prune}")

Store adapter protocol

Implement the MemoryStore protocol to connect fademem to your existing memory system:

from fademem import MemoryStore, prune_memories

class MyMemoryStore(MemoryStore):
    def get_memories(self):
        # Return memories from LangChain, Mem0, your database, etc.
        ...
    def archive_memories(self, memory_ids):
        # Move to archive or mark as archived
        ...
    def delete_memories(self, memory_ids):
        # Permanently remove
        ...

# Score and prune in one call
decisions = prune_memories(
    MyMemoryStore(),
    model="power-law",
    now=87_400_000,
    scale_millis=86_400_000,
    exponent=1.0,
    threshold=0.25,
    action="archive",  # or "delete"
)

Native acceleration

The Python package bundles a platform-native shared library (Go c-shared build) and calls it through ctypes. If the native library is unavailable, it transparently falls back to a pure-Python reference implementation with identical results.

Install (Go CLI)

go build -o decay-sweep ./cmd/decay-sweep

Or install directly:

go install github.com/iamfaham/fademem/cmd/decay-sweep@latest

CLI usage

# Dry-run: scan and report, no file changes
decay-sweep \
  --input memories.jsonl \
  --mode dry-run \
  --model exponential \
  --now-ms 87400000 \
  --half-life-ms 86400000 \
  --threshold 0.5 \
  --workers 4

# Archive: move pruned records to a separate file
decay-sweep \
  --input memories.jsonl \
  --archive archive.jsonl \
  --audit audit.jsonl \
  --mode archive \
  --model power-law \
  --now-ms 87400000 \
  --scale-ms 86400000 \
  --exponent 1.0 \
  --threshold 0.25 \
  --workers 4

# Delete: remove pruned records in place (requires --confirm-delete)
decay-sweep \
  --input memories.jsonl \
  --audit audit.jsonl \
  --mode delete \
  --confirm-delete \
  --model exponential \
  --now-ms 87400000 \
  --half-life-ms 86400000 \
  --threshold 0.5 \
  --workers 4

CLI flags

Flag	Default	Description
--input	(required)	JSONL memory-store file
--mode	dry-run	dry-run, archive, or delete
--model	exponential	exponential or power-law
--archive	(empty)	Archive output file (required for archive mode)
--audit	(empty)	Structured JSONL audit output
--confirm-delete	false	Required for delete mode
--now-ms	0	Evaluation time in Unix epoch milliseconds
--half-life-ms	0	Exponential half-life in milliseconds
--scale-ms	0	Power-law scale in milliseconds
--exponent	0	Power-law exponent
--threshold	0	Prune scores strictly below this value
--workers	1	Bounded concurrent score calculations (max 1024)
--version	false	Print version and exit

JSONL record format

Each line is a JSON object with three fields:

{"id": "unique-memory-id", "last_accessed_ms": 87400000, "importance": 0.8}

• id: non-blank string
• last_accessed_ms: signed integer, Unix UTC epoch milliseconds
• importance: float in [0, 1] (used by power-law model; ignored by exponential)

Native C ABI

The Go engine exports two functions through a c-shared library:

int32_t DecayScoreExponential(int64_t last_accessed, int64_t now, int64_t half_life_ms, double* out_score);
int32_t DecayScorePowerLaw(int64_t last_accessed, int64_t now, int64_t scale_ms, double exponent, double importance, double* out_score);

• Only fixed-width scalars cross the boundary: int64_t, double, int32_t.
• No Go pointers, strings, structs, callbacks, or caller-visible allocations.
• Status codes: 0 = OK, 1 = invalid argument, 2 = null output.
• The caller owns the double* output pointer.

Platform support

Platform	Native library	Wheel	CI verified
Windows x86_64	fademem.dll	py3-none-win_amd64	Yes
Linux x86_64	libfademem.so	py3-none-manylinux_2_28_x86_64	Yes
macOS ARM64	libfademem.dylib	py3-none-macosx_14_0_arm64	Yes
macOS Intel x86_64	Not supported in v0.1.0 (GitHub-hosted runner unavailable)	—	—

Native libraries are built on GitHub-hosted runners. No cross-compilation is claimed.

Mutation safety

• Dry-run: no file changes.
• Archive: writes retained and pruned records to sibling temporary files, syncs, then atomically replaces the archive file first, then the input file.
• Delete: writes retained records to a sibling temporary file, syncs, then atomically replaces the input file.
• Audit: streamed to a sibling temporary file, synced, and atomically replaced.
• Path collisions between input, archive, and audit are rejected before any mutation.
• The CLI processes records in source order with bounded concurrent scoring (one batch of max(1, workers) * 4 records in memory at a time).

Development

# Go tests
go test ./cmd/decay-sweep ./internal/ffi ./internal/sweep ./pkg/decay

# Python tests
cd python
uv run --with pytest --with hatchling pytest

# Build native library
go build -buildmode=c-shared -o dist/libfademem.so ./native

# Stage and build wheel
python scripts/stage_native.py --source dist/libfademem.so --target-directory python/src/fademem/_native
cd python && uv build --wheel

License

MIT