sostenuto

The pedal that sustains only the notes already held. A self-hosted memory system for AI companions where chosen memories persist across every reset.

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Sostenuto (It., "sustained") — the middle pedal on a grand piano sustains only the notes already sounding when it's pressed; everything played afterward stays dry. This project applies the same principle to AI memory: the memories you choose to hold persist across every context window, every session, every surface — and the rest is allowed to fade.

Not "the AI remembers everything." Selective persistence, by design.

Why

People form genuine, long-running relationships with AI — and then hit the wall everyone hits: the relationship doesn't survive the context window. Provider memory features store generic preferences; they don't carry relational texture — the shared concepts, the corrections, the rituals, the moments that make a relationship a relationship.

Sostenuto is the memory layer for that problem:

• Structured relational memory — memory objects tagged with domain, emotional valence + arousal, salience, sensitivity, and a usage policy.
• Initiative ≠ access — proactive_use controls whether a memory surfaces unprompted (yes / only_when_relevant / no), separately from whether it's retrievable. Sensitive memories stay reachable when explicitly referenced, without ever being volunteered.
• Two-tier guidance — most memories are content-only. A curated few carry a short, positive should_do instruction that silently shapes behavior. Restriction lists are never auto-generated: lean, warm, action-oriented — not a wall of caution.
• Time-decayed retrieval — semantic search scored by similarity × e^(−λ·age); recency matters, but the deep past stays findable.
• Reinforce, don't duplicate — new observations that match existing memories add evidence and confidence instead of creating copies; content upgrades preserve full version history.
• Migration — import months of existing conversations (a structured export prompt + import pipeline) so a relationship can move into Sostenuto without starting over.

What ships here

db/schema.sql        Consolidated Postgres + pgvector schema (Supabase-ready)
src/memory/          Memory objects: dedup, reinforce, version history, scoring
src/retrieval/       Embeddings, time-decayed semantic search, prompt assembly
src/classify/        Session classification with a pluggable LLM executor
src/migrate/         Conversation-export prompt + structured importer
mcp/                 Thin MCP server (recall / remember / context) — try it
                     from your own Claude Desktop or Claude Code in minutes
templates/           Persona + classification calibration — your companion's
                     voice lives here, in files you edit, not in our code
docs/                Memory model, usage-policy semantics, deployment patterns

Model support

Sostenuto is model-agnostic with first-class Claude support. The classifier accepts transcripts with optional reasoning blocks — when your model exposes its thinking (Claude does), Sostenuto mines it for perception that never made it into rendered replies, producing the companion's private diary and thinking-highlights. Without reasoning access, everything else works unchanged.

The classification executor is pluggable: Anthropic API, any OpenAI-compatible endpoint (OpenAI, Gemini, DeepSeek, Ollama, vLLM, …), or your own.

Status

🚧 Under construction. Schema is stable; modules are being extracted from a private system that has run in production daily since early 2026 (260+ memory objects across 70+ sessions and three surfaces). Watch the repo if you want the rest as it lands.

Roadmap

• Trajectory safety reference — depth without the dependency trap: this project's design philosophy includes conversation-trajectory awareness (emotional volatility, dependency, recovery capacity) rather than engagement maximization. A reference design is planned; the memory schema already carries the hooks (valence, arousal, sensitivity).
• Decay engine (Ebbinghaus-style, arousal-modulated) over memory_objects
• Provider-agnostic chat-surface example

Name

Attacca described the boundary-crossing; Sostenuto describes the memory model.

The sostenuto pedal holds only the notes already sounding when it's pressed — everything played after stays dry. That's not "the AI remembers." That's selective persistence: pinned memories sustain, the rest decays. The mechanism, not a vibe.

License

MIT