Posts in the AI Agent 記憶工程 series
Agent memory is not one feature — it is at least four distinct engineering problems: working, episodic, semantic, and procedural. This ten-part series walks through the full design space, from taxonomy to coding agent implementations, platform APIs, open-source frameworks, security attack surfaces, and 2026 trend analysis.
CoALA splits agent memory into working, episodic, semantic, and procedural — but the four-cell taxonomy alone doesn't explain why Claude Code uses Markdown files while Mem0 uses vectors. This post adds six independent design axes (read mode, write timing, fidelity, write authority, forgetting, scope) and a file-to-graph spectrum to map the full design space of agent memory systems in 2026.
Chroma's controlled study shows that even when it fits, a full context degrades performance. Coding agent vendors have landed on seven different responses: compact, hand off, prune, defer loading, isolate, train it into the model, or change the unit of work. Amp removed /compact outright, Atlassian argues summarization should be a last resort, and Cursor's A/B test measured a 46.9% token reduction. The three real disagreements come down to what each team is measuring.
Nine coding agents have taken at least four different paths for long-term memory: Claude Code and Codex use Markdown files (agent-written, human-readable), Antigravity CLI inherits Gemini CLI's approval inbox (agent proposes, human decides), and Copilot uses citations with JIT verification (auto-deleted after 28 days unverified). Cursor removed its Memories feature and fell back to human-written Rules. Hermes Agent, OpenClaw, and Letta Code treat memory as a core harness component, not a plugin. Their choices on write timing, forgetting, and cross-team sharing are completely different — and none has published a controlled experiment on whether their memory system actually helps.
All five major cloud platforms shipped agent memory APIs in 2025–2026, but their design philosophies diverge sharply: OpenAI writes memory as files, Anthropic mounts memory as a directory, Google uses vectors with topic classification, AWS combines events with pluggable strategy pipelines, and Microsoft abstracts memory behind context providers. Pricing ranges from free to $0.75/1K records/month; tenant isolation spans from 'your app handles it' to IAM as a first-class citizen.
Seven open-source memory frameworks span the spectrum from auto-extracted vectors to human-readable files: Mem0's one-line add(), Graphiti's bi-temporal knowledge graph, Letta's agent-edited system-prompt blocks, LangGraph's namespaced Store, LlamaIndex's priority-based block truncation, Cognee's triple-store pipeline, and Supermemory's temporal vector-graph engine. This post compares their storage, write/forget mechanics, tenant isolation, and benchmark numbers, then offers selection guidance for four common scenarios.
Mem0 sits between an agent and storage: it extracts durable facts from interactions, scopes them by user, agent, or run, and searches them before a later generation. Its appeal is a small API; its risks are extraction errors, stale memories, and authorization boundaries.
Volcano Engine's open-source OpenViking stores agent memory, knowledge, and skills as a viking:// virtual filesystem — browsable with ls, tree, and find. Three-tier loading (L0/L1/L2) averages just 550 tokens per retrieval, boosting LoCoMo memory accuracy from 24–57% to 80–83%.
Memory turns prompt injection from a one-shot nuisance into a persistent backdoor: MINJA shows conversation-only injection succeeds >95% of the time, and SpAIware demonstrated continuous data exfiltration via planted memories. The industry's two defensive lines — citation-based verification (Copilot) and human approval inboxes (Gemini CLI / Devin) — each have blind spots.
In H1 2026, OpenAI, Anthropic, Letta, and LangChain independently chose Markdown files + indexes over vector databases; write permissions shifted back to humans; forgetting mechanisms appeared but nobody implemented Ebbinghaus; Penfield Labs caught 6.4% wrong answers in LoCoMo; three vendors simultaneously adopted 'Dreaming' for offline memory consolidation. Five trends, one conclusion: memory is not a feature — it is an architecture decision.