`decay` is a per-project boolean that turns on [Memory Decay](/platform/features/memory-decay) — a search-time ranking bias that reinforces recently-accessed memories and gently dampens stale ones. The flag is `false` by default; set it via the same project-update endpoint:
The current state is returned on every project read (and supports `?fields=decay` for a minimal response). Toggling has no effect on stored memories, only on how v3 search ranks them.
@@ -4,6 +4,13 @@ description: "Release notes for the Mem0 hosted platform — backend, dashboard,
mode: "wide"
---
<Update label="2026-05-04" description="">
**New Features:**
- **Memory Decay:** Per-project search-time ranking bias that boosts recently-used memories and gently dampens stale ones. Opt-in via `decay` on the project endpoint; off by default. The scaling factor stays in `0.3×–1.5×`, the public `score` remains clamped to `[0, 1]`, and the bias never filters a candidate out. See [Memory Decay docs](/platform/features/memory-decay).
@@ -187,6 +187,7 @@ If the user is on a pre-current major (Python < 2, TS < 3, or Platform `output_f
- [Criteria-Based Retrieval](https://docs.mem0.ai/platform/features/criteria-retrieval) [Platform]: Use when targeting memories by custom criteria, not just semantic similarity.
- [Contextual Add](https://docs.mem0.ai/platform/features/contextual-add) [Platform]: Use when `add()` should consider the surrounding conversation, not just the latest turn.
- [Custom Instructions](https://docs.mem0.ai/platform/features/custom-instructions) [Platform]: Use when tailoring what Mem0 extracts and stores on Platform.
- [Memory Decay](https://docs.mem0.ai/platform/features/memory-decay) [Platform]: Use when search results should boost recently-reinforced memories and dampen stale ones — opt-in per project, search-time only, never filters candidates out.
- [Advanced Memory Operations](https://docs.mem0.ai/platform/advanced-memory-operations) [Platform]: Use when basic CRUD is not enough - batch ops, complex filters, workflows.
description: "Boost recently-used memories and gently dampen stale ones at search time, without filtering anything out."
---
# Memory Decay
Older memories drift in relevance at different speeds. A user's coffee order matters every morning; a one-off project name from last quarter rarely matters again. Memory Decay makes that intuition explicit at search time: every time a memory is returned in a search it gets a small reinforcement, and memories that haven't been touched in a while have their ranking score gently dampened.
It is **a soft ranking bias, never a filter.** Decay never zeroes a candidate out — at worst it scales its score by `0.3×`. Anything that would have surfaced without decay can still surface with decay on, just with a different ranking among similarly-scored results.
<Info>
**Use Memory Decay when…**
- Search results are crowded with old facts the user no longer cares about.
- You want recently-used memories to drift to the top automatically — without writing custom scoring logic.
- You want this preference applied per project so cohorts can be compared side-by-side.
</Info>
<Warning>
Memory Decay is **opt-in per project** and **off by default**. Search behavior is bit-identical to today until you turn it on. The toggle applies to v3 search only.
</Warning>
## How it works
Every memory carries a small piece of bookkeeping: when was it last retrieved, and how often. Memory Decay turns that history into a *scaling factor* in the range `0.3×` to `1.5×` and multiplies it into the ranking score at search time.
| Memory state | Scaling factor | Ranking effect |
|---|---|---|
| Just accessed | ≈ **1.5×** | Strong boost |
| Touched today | 1.2 – 1.4× | Mild boost |
| Idle for a few days | 0.6 – 1.0× | Mild dampening |
| Idle for many months / years | ≈ **0.3×** | Floor — never lower |
The bounds matter: `0.3` is the floor and `1.5` is the ceiling, so decay can meaningfully reorder candidates without ever dominating the underlying relevance score.
At search time the pipeline:
1. Widens the candidate pool (`top_k × 3`, with a floor of 50) so reordering has room.
2. Multiplies each candidate's score by its scaling factor.
3. Sorts on the unclamped product so the full `0.3×–1.5×` range can rearrange candidates.
4. Returns the public `score` clamped to `[0, 1]` so the API contract is preserved.
5. Truncates to the `top_k` you requested.
6. Records a fire-and-forget reinforcement against each returned memory — its access history grows by one, capped at the most recent 20 touches.
Memories created before decay was enabled don't yet have an access history. They use a sensible fallback: their `updated_at` is treated as a single past touch, so the same scale above applies based on how stale that update is — a recently-updated legacy memory enters near the neutral band, a long-stale one sits closer to the floor. Once surfaced in a search after decay is on, they accumulate access history naturally and behave like any other memory.
## Configure access
- Set `MEM0_API_KEY` in your environment, or pass it to the SDK constructor.
- Initialize the client with the organization and project you want to scope to.
The toggle lives on the project. You enable decay by patching the project's `decay` field; everything else — your `add` calls, your `search` calls, your application code — stays exactly the same.
## Enable decay for a project
### 1. Turn the flag on
The toggle is exposed on the standard project-update endpoint, the same place where `multilingual` and `custom_categories` live.
The toggle is fully reversible. Setting it to `false` immediately restores the pre-decay ranking; nothing about your stored memories is modified or lost.
The toggle is idempotent. Re-applying the same value is a no-op, and access history accumulated while decay was on is preserved if you flip it back on later.
</Note>
## What changes when decay is on
- **Search ranking reorders.** A relevant memory you reinforced an hour ago will tend to outrank an equally-relevant memory that was last touched a month ago.
- **The candidate pool over-fetches** to give the scaling factor room to reorder. You still get exactly the `top_k` you requested, but the items returned can come from a deeper slice of the pre-decay ranking than before.
- **The public `score` field stays in `[0, 1]`.** Even when the internal product exceeds 1, the field returned to the client is clamped, so existing assertions and downstream UI logic continue to work.
## What stays the same
- **Public API shape** — every endpoint accepts the same parameters and returns the same fields. You don't touch your client code.
- **Threshold semantics on the request side** — your `threshold` is still applied during candidate selection.
- **Memory creation and storage** — every new memory still lands the same way. Decay is a search-time concern.
Because the scaling factor is applied *after* the threshold filter has already run, an item that passed the request `threshold` can come back with a public `score` slightly below it (a stale candidate dampened by `0.3×`). This is intentional — decay is a soft bias, not a filter. If you require a hard `score >= threshold` invariant on the response, filter client-side after the call.
| Reinforced on a recent search | 1.2 – 1.5× | Sustains its boost for the next several searches. |
| Idle for a few days | 0.6 – 1.0× | Falls back into the neutral band. |
| Idle for weeks | 0.4 – 0.6× | Mild dampening — can still surface for strong matches. |
| Pre-decay legacy memory (no access history) | 0.3 – 1.0× | Falls back to `updated_at`: recently-updated entries land near 1.0×, long-stale entries approach the 0.3× floor. |
The reinforcement is bounded: each memory tracks at most the last 20 access timestamps, so the boost stays well-behaved no matter how many times a memory is retrieved.
## FAQ
**Will decay ever drop a result that would otherwise surface?**
No. The floor is `0.3×` — the scaling factor can dampen a score, never zero it. Threshold filtering happens *before* decay, so any candidate that cleared the threshold is in the pool decay reorders.
**Why is the public score sometimes below my requested threshold?**
The threshold is applied to the candidate pool pre-decay; the scaling factor then reshapes scores in the `0.3×–1.5×` band. A stale-but-relevant candidate can come back with a final score slightly under your threshold by design — the candidate stays visible but visibly dampened. Filter client-side if you need a hard floor on the response.
**Does decay change how I add memories?**
No. The `client.add(...)` path is unchanged. Decay is a search-time ranking adjustment.
**What if I had memories before turning decay on?**
They use a fallback: the memory's `updated_at` is treated as a single historical touch, so the same scaling applies based on how stale that update is — a recently-updated legacy memory enters near the neutral band (~1.0×), a long-stale one closer to the floor (~0.3×). Once retrieved they accumulate access history and behave like any other memory.
**Can I tune how aggressively decay scales scores?**
Not in this version. The current scaling is calibrated to be conservative — wide enough to meaningfully reorder candidates, narrow enough to never dominate the underlying relevance score. Per-project tuning is on the roadmap.
**Can I see the scaling factor per result?**
Internal scoring details are persisted on the search Event for support and debugging. They aren't exposed in the public response by design — the response surface stays a single `score` field.
**Does decay interact with reranking?**
Yes — they layer cleanly. The reranker produces a richer relevance score; decay then biases that score by reinforcement history before final truncation to `top_k`.
## What's next
This release is deliberately the simplest version of decay we could ship — every memory contributes to ranking through its access history alone, so the signal can be evaluated in isolation. On the roadmap:
- **Category-aware weighting.** A fact tagged `health` will be able to carry more weight than a passing observation tagged `misc`, so important categories don't get dampened the same way as noise.
- **Auto-tuning per project.** Project-scoped automatic adjustment of how aggressively decay scales scores, based on observed access patterns — replacing the fixed scaling band with one that fits your workload.
Both extensions are forward-compatible — no migration on your side will be needed when they ship.
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