14 — Retrieval, memory, and state offloading

TL;DR

• The only vendor-published token numbers in this space: Anthropic's context editing cut token consumption 84% in a 100-turn web-search eval and improved task performance 29% alone, 39% combined with the memory tool (claude.com/blog/context-management; re-). T1, but a search-heavy self-eval — not coding — and the docs themselves warn each clear invalidates cached prefixes.
• Compaction is rented, not free: the API bills the summarization pass as a separate iteration at full price (docs example: 180k input + 3.5k output ≈ $1.98 per pass at Fable 5 list, ESTIMATE), and top-level usage fields exclude compaction iterations — naive cost dashboards undercount compacting sessions.
• Local measurement (this repo): pointer-architecture instructions keep 41,751 of 44,495 instruction tokens (93.8%) lazy; loading them eagerly instead would add ESTIMATE ~$7.64/day (+35%) on the modeled heavy-day profile. @imports do NOT defer — docs confirm they load at launch.
• Local measurement: a pointer to a decision log is 53 tokens vs 233 for restating it (77.3% cut/item, not the ~95% folklore implies); a realistic handoff/progress file is 387 tokens and replaces transcript replay — the vendor endorses this pattern with zero published measurements.
• Third-party memory products are QUALITY-TRADE: Mem0's >90% token cut is real arithmetic but loses accuracy to do-nothing baselines (Letta files-only 74.0% vs Mem0 68.5% on LoCoMo; ConvoMem: full-context 70–82% vs Mem0 30–45%). Semantic response caching (61.6–68.8% hit rates) is FAQ-workload evidence only — nothing for coding agents.

Where this layer sits in the spend

On the modeled session profile (local phase-0 measurement: ~6 sessions/day, 19 API calls/session, 5.5k uncached input, 85k cache-write, 1.17M cache-read, 27k output, ~$22/day), retrieval/memory/state techniques act on the input side: cache reads 32% + cache writes 29% + uncached input 2% = 63% of dollars. The mechanism is always the same: replace re-replay (transcript) and re-derivation (re-exploring the codebase) with recall from a cheap external store — disk files, a memory directory, or a billed summary. Output-side techniques are in 15-output-discipline.md; cache mechanics in 13-caching-exploitation.md; the measurement harness in 31-validation-harness.md.

Local measurements (jackin repo, method: python3 /tmp/ct.py claude-fable-5 < file → count_tokens API)

Techniques

1. Pointer-architecture instruction files — slim always-on index, on-demand topic files

One-line pitch: keep a small index loaded every session; defer detail to files the model reads only when relevant. The single highest-confidence win in this file.

• Layer: input (prompt architecture / repo file layout)
• Mechanism: Claude Code loads root CLAUDE.md in full every session; nested CLAUDE.md and paths:-scoped rules load only when matching files are read; plain-link topic files load only when the model chooses to read them. Docs: "Splitting into @path imports helps organization but does not reduce context, since imported files load at launch" and "target under 200 lines per CLAUDE.md... Longer files consume more context and reduce adherence" (code.claude.com/docs/en/memory). Bonus: block-level HTML comments are stripped before injection — token-free maintainer notes (same page).
• Expected savings: local measurement above: 41,751 tokens kept lazy vs 2,744 eager. Counterfactual all-eager on the modeled profile (ESTIMATE, arithmetic): +41,751 tok cache-write/session ($12.5/MTok = $0.52) + 18 subsequent calls × 41,751 cache-read ($1/MTok = $0.75) ≈ $1.27/session, $7.64/day (+35%). Upper bound — each topic file actually read mid-session claws back its share (typical session reads 1–2 of 12, late-positioned).
• Evidence tier: T1 (documented harness behavior, code.claude.com/docs/en/memory + /context-window) + local measurement (table above; lazy injection of docs/CLAUDE.md observed live this session).
• Quality risk: NEGATIVE-COST — docs assert shorter files improve adherence (their claim, unmeasured). Failure mode: model skips a pointer it should follow; mitigate by making each index line state that a rule exists and where detail lives (this repo's pattern). Degradation manifests as violations of deferred rules.
• Availability: CLAUDE-CODE-TODAY
• Effort to adopt: hours (split CLAUDE.md into index + topic files / paths: rules; convert @imports to plain references)
• Composability: multiplies with prompt caching (smaller stable prefix, see 13-caching-exploitation.md); survives /compact (root index re-injected from disk); topic files compress further with caveman-compress (local phase-0: 58.5% token cut on prose). Anti-synergy: none known.
• Validation protocol: A/B 10 matched tasks: branch A = current index+topic layout, branch B = everything inlined in root CLAUDE.md. Compare per-session input tokens (OTLP/ccusage), task pass rate, and count violations of rules whose detail lives in deferred files. Success = B costs more with no adherence gain for A.

2. Compaction-resistant state placement — engineer what survives /compact

One-line pitch: Claude Code documents an exact survival table; put durable state in surviving locations so aggressive compaction stops losing instructions.

• Layer: turn-structure (harness behavior) + repo file layout
• Mechanism: (code.claude.com/docs/en/context-window#what-survives-compaction): system prompt/output style unchanged; project-root CLAUDE.md, unscoped rules, and auto memory re-injected from disk; paths: rules and nested CLAUDE.md lost until a matching file is read again; invoked skill bodies re-injected but "capped at 5,000 tokens per skill and 25,000 tokens total; oldest dropped first", truncation keeps the start of SKILL.md; hooks unaffected. Bonus detail from the same page's simulation: the startup skill listing is NOT re-injected after /compact — only skills actually invoked are preserved.
• Expected savings: loss-prevention, not direct: avoids re-explaining lost instructions (fresh input + output at ~5x input price). Enables compacting earlier/harder. Docs add the cost rationale for /clear: "Old conversation crowds out the files you need next and costs tokens on every message"; /compact focus on X steers the summary.
• Evidence tier: T1 (shipped behavior, precisely documented; table re-)
• Quality risk: NEGATIVE-COST — pure correctness improvement. Residual: skills >5k tokens silently truncate after compaction (put critical instructions at the top of SKILL.md); nested-file rules vanish until the subtree is touched.
• Availability: CLAUDE-CODE-TODAY
• Effort to adopt: minutes-to-hours (move must-survive rules to project root / unscoped rules; keep task state in files, not chat)
• Composability: foundation for techniques 3, 4, 5; orthogonal to API-side compaction (technique 8).
• Validation protocol: scripted session establishes 10 instructions across locations (conversation-only, nested CLAUDE.md, paths: rule, root CLAUDE.md, auto memory), force /compact, probe each instruction with a question; score retention per location, 5 repetitions. Expect retention to match the docs table exactly.

3. Claude Code auto memory (MEMORY.md) — model-written notes with a hard load cap

One-line pitch: Claude writes its own per-repo memory and reloads it every session — recall replaces re-derivation at a bounded, documented cost.

• Layer: input (harness product feature)
• Mechanism: default-on since v2.1.59. ~/.claude/projects/<project>/memory/ holds MEMORY.md ("The first 200 lines of MEMORY.md, or the first 25KB, whichever comes first" load at session start) plus topic files "not loaded at startup — Claude reads them on demand". Re-injected from disk after compaction. Toggles: /memory, autoMemoryEnabled, CLAUDE_CODE_DISABLE_AUTO_MEMORY=1. Notably: "CLAUDE.md files are loaded in full regardless of length" — the model's memory is budgeted; yours is not. (All quotes code.claude.com/docs/en/memory.)
• Expected savings: none published anywhere. Cost side bounded (ESTIMATE): worst case 25KB ≈ 25,600 chars ÷ 3.35 chars/tok (local phase-0 Fable-5 prose ratio) ≈ 7,642 tok/session start → write $0.10 + 18 reads $0.14 ≈ $0.23/session, $1.40/day (6.4% of the modeled $22 day). At the docs' representative 680-token MEMORY.md: ~$0.02/session, $0.12/day. Savings side (avoided re-exploration of build/test/architecture) is real but unmeasured — top local-experiment candidate.
• Evidence tier: T1 for mechanism and caps (live docs); savings claim T4 until measured.
• Quality risk: NEUTRAL→NEGATIVE-COST. Risks: silent context spend whether useful or not; stale/wrong self-written notes steering the model. Everything is auditable plain markdown via /memory.
• Availability: CLAUDE-CODE-TODAY
• Effort to adopt: zero (default-on); curation minutes/week (prune MEMORY.md; keep under the 200-line window)
• Composability: survives /compact (technique 2); handoff files (4) can live in the memory dir to auto-load; caveman-compress on MEMORY.md pulls more content under the load cap. Open question: whether the MEMORY.md block sits in the cached prefix (it loads at startup so it should; per-session writes churn the next session's prefix — cache-write at 1.25x, see gaps).
• Validation protocol: matched task pairs in fresh sessions with autoMemoryEnabled on vs CLAUDE_CODE_DISABLE_AUTO_MEMORY=1; measure tokens-to-completion and count re-exploration tool calls (re-running discovery greps/reads); diff /context. Success = on-condition saves more than its startup tax with equal pass rate.

4. File-based handoff/progress state — resume from a small state file, not a transcript

One-line pitch: end sessions by writing progress/decisions to files; boot the next session from them — Anthropic's published long-running-agent pattern, locally costed at 387 tokens per handoff.

• Layer: turn-structure (workflow / orchestrator pattern)
• Mechanism: Anthropic engineering : initializer session creates init script + claude-progress file + feature checklist; each session boots from those, works one feature, verifies end-to-end, updates the log ("recovers the full state of the project in seconds"; "This approach saves Claude some tokens in every session"). The memory-tool docs codify the same as the "multi-session software development pattern" . Manus generalizes: "the file system as the ultimate context: unlimited in size, persistent by nature" with todo.md recitation across ~50-tool-call tasks (manus.im blog). Production sibling: jackin' uses a shared COORDINATION.md claimed via stable agent codenames for parallel-agent state.
• Expected savings: vendor: qualitative only — no published numbers (T1 as practice, quantitatively T4/local). Local proxies (/tmp/ct.py): realistic 21-line handoff file = 387 tokens; booting from it replaces transcript resumption or re-exploration that costs tens of thousands of input tokens (ESTIMATE: re-reading 5 source files ≈ 10–40k tok; a /resume replays the full prior conversation). Per-item recall is technique 5's 77.3%.
• Evidence tier: T1 as shipped practice (Anthropic harness, Manus, memory-tool docs); no published token measurements anywhere — flagged as the field's most fillable gap.
• Quality risk: NEGATIVE-COST direction per Anthropic (their motivation is reliability; one-feature-at-a-time "keeps the progress log trustworthy"). Failure mode: stale state files mislead the next session — mitigated by verify-before-marking-complete.
• Availability: CLAUDE-CODE-TODAY (plain markdown + git; SessionEnd hooks or an orchestrator automate it)
• Effort to adopt: minutes (manual) / hours (hook-automated)
• Composability: composes with /clear (clear cheaply because state is externalized), auto memory (3), compaction (files survive by definition, technique 2), and subagent fan-out (each agent reads the same state file).
• Validation protocol: same multi-session feature three ways: (a) handoff file + /clear, (b) /resume transcript replay, (c) ride auto-compact. Sum billed tokens per arm (OTLP per-session), grade task completion. No one — including Anthropic — has published this comparison; see 31-validation-harness.md.

5. Restorable compression — drop the bytes, keep the handle

One-line pitch: evict bulky content from context but keep the pointer that re-fetches it (URL, path, decision-ID); eviction never destroys information.

• Layer: input / turn-structure (prompt discipline; embodied server-side in context-editing placeholders)
• Mechanism: Manus production rule: "the content of a web page can be dropped from the context as long as the URL is preserved, and a document's contents can be omitted if its path remains available in the sandbox" (manus.im). Anthropic's context editing ships the same shape server-side: cleared tool results become placeholders while tool-call inputs are kept by default (clear_tool_inputs: false) — the "how to re-fetch" survives. Applied to decisions: keep a numbered DECISIONS.md; in-context references shrink to "Decision #14 (path)".
• Expected savings: local measurement : restatement 233 tok vs pointer 53 tok = 77.3% per recalled item (sweep's independent sample: 79.3%). Kills the "a pointer is ~10 tokens" folklore — useful pointers carry path + gist. Scales with restatement frequency (unmeasured; needs transcript mining). Cache side-benefit: pointers are often byte-identical across turns, restatements never are — preserves prefix stability (13-caching-exploitation.md). Manus frames the payoff via cache economics: cached input 10x cheaper (their $0.30 vs $3.00/MTok matches Anthropic's 0.1x cache-read ratio, cross-checked against reference pricing); "KV-cache hit rate is the single most important metric for a production-stage AI agent"; Manus input:output ≈ 100:1 (vendor figure, no methodology).
• Evidence tier: T1 as production practice (Manus; Anthropic context-editing design), local quantification for the per-item cut; no end-to-end published number.
• Quality risk: NEGATIVE-COST when targets are stable (git paths, numbered log); RISKY when targets drift (renamed files, mutable URLs) — the model recalls a pointer to nothing. Degradation manifests as failed re-fetches; falsify by sampling references and checking resolution.
• Availability: CLAUDE-CODE-TODAY
• Effort to adopt: minutes (DECISIONS.md + a CLAUDE.md line: cite, don't restate)
• Composability: core enabler of context editing (7), handoff files (4), and subagent result summarization; anti-synergy: none, but over-pointering forces re-fetch tool calls (each ~ a tool round-trip).
• Validation protocol: instruct via CLAUDE.md to cite the decision log rather than restate; sample 20 in-transcript references; measure tokens/reference and the re-fetch success rate when the model needs detail. Success = ≥95% resolution with per-item cut near 77%.

6. Anthropic API memory tool (memory_20250818, beta) — cross-session file memory

One-line pitch: the model stores/recalls learnings in a client-side /memories directory persisting across conversations — recall instead of re-derive, vendor-evaluated only in combination with context editing.

• Layer: infra (API/SDK tool + client-side handler)
• Mechanism: tool type memory_20250818 with view/create/str_replace/insert/delete/rename against a directory you host. Enabling it auto-injects a protocol prompt ("ALWAYS VIEW YOUR MEMORY DIRECTORY BEFORE DOING ANYTHING ELSE... ASSUME INTERRUPTION: Your context window might be reset at any moment") — locally measured at 189 tokens (Fable 5, /tmp/ct.py) of standing cost once enabled. Docs prescribe the multi-session pattern (initializer session → progress log → end-of-session update) and position memory as what "persists important information across compaction boundaries so that nothing critical is lost in the summary". ZDR-eligible. (platform.claude.com/docs/en/agents-and-tools/tool-use/memory-tool.)
• Expected savings: vendor: memory + context editing = +39% task performance over baseline on an internal agentic-search eval (claude.com/blog/context-management, re-); token savings never isolated for memory alone — the 84% belongs to context editing. Recall-vs-rederive savings unquantified by anyone. Memory writes bill as output (~5x input).
• Evidence tier: T1 (shipped beta; vendor self-eval; no third-party replication found)
• Quality risk: NEGATIVE-COST per vendor eval (performance up AND enables otherwise-failing long workflows). Risks: stale/cluttered memory degrades behavior (docs ship an anti-clutter prompt); path-traversal security is your handler's burden.
• Availability: SDK (Developer Platform, Bedrock, Vertex; public beta). NOT-USER-ACCESSIBLE inside Claude Code — auto memory (technique 3) is the product analogue.
• Effort to adopt: days (client-side handler via BetaAbstractMemoryTool / betaMemoryTool helpers; storage + security)
• Composability: designed to stack with context editing (7) and compaction (8); memory reads are ordinary tool results, cacheable as prefix.
• Validation protocol: 3-session SDK project run with vs without the memory tool: measure tokens/session, completion rate, and audit the memory directory for clutter after session 3. Vendor numbers are combined-stack only, so isolate memory's contribution.

7. Context editing (clear_tool_uses_20250919 / clear_thinking_20251015, beta)

One-line pitch: server-side eviction of stale tool results/thinking instead of carrying them forever — the 84% headline lives here, with a cache-invalidation tax the docs admit and nobody has priced.

• Layer: input + cache (API request parameter, beta header context-management-2025-06-27)
• Mechanism: API strips old tool results (default trigger 100,000 input tokens; default keep: 3 most recent tool uses; optional clear_at_least) and/or old thinking blocks before the model sees the prompt, replacing them with placeholders; tool-call inputs kept by default. Client retains full history; response reports context_management.applied_edits[].cleared_input_tokens. (platform.claude.com/docs/en/build-with-claude/context-editing, re-.)
• Expected savings: vendor: 84% token reduction + workflow completion in a 100-turn web-search eval; +29% performance from editing alone (claude.com/blog/context-management). Cache trap, quoted: clearing "Invalidates cached prompt prefixes... clear enough tokens to make the cache invalidation worthwhile." Break-even (ESTIMATE, derivation): clearing C tokens ahead of a suffix of S still-kept tokens forces re-writing S at $12.5/MTok instead of reading at $1 → extra S×$11.5/M; each later call then reads C fewer tokens (C×$1/M). Break-even calls N* ≈ 11.5 × S / C. Examples: C=40k, S=15k → 4.3 calls (pays off mid-session); C=5k, S=60k → 138 calls (never pays). With the local cache-hot mix (92.83% of heavy-session input = cache reads, phase-0), small frequent clears are plausibly net-negative — contradicting "context editing is pure savings".
• Evidence tier: T1 (shipped beta, vendor-published measurements); break-even arithmetic is local ESTIMATE; the 84% is search-workload, unreplicated externally.
• Quality risk: NEGATIVE-COST per vendor on search workloads; RISKY for coding sessions where old tool results get re-referenced (cleared content must be re-fetched: extra tool round-trips). exclude_tools protects critical tools' results.
• Availability: SDK / GATEWAY-OR-SELF-HOST. Not a Claude Code knob (Claude Code ships its own compaction/microcompaction instead).
• Effort to adopt: minutes on SDK (one request field)
• Composability: pairs with memory tool (6: persist before clearing) and compaction (8); follows technique 5's evict-bytes-keep-handle shape. Anti-synergy: prompt caching — every clear churns the prefix.
• Validation protocol: replay a recorded coding session via SDK with clearing off vs on at several clear_at_least values; sum billed input + cache-write tokens (including re-writes) and count re-fetches of cleared content; diff final-answer quality. Derives the empirical break-even to compare with N* above.

8. Server-side compaction (compact_20260112, beta) — transcript replaced by a billed summary — QUALITY-TRADE

One-line pitch: the API summarizes the conversation and drops everything before the compaction block — sessions extend indefinitely, but you pay full price for the summarization pass and the summary is lossy by construction.

• Layer: turn-structure + cache (API, beta header compact-2026-01-12)
• Mechanism: default trigger 150,000 input tokens (minimum 50,000); API emits a compaction block and "automatically drops all message blocks prior to the compaction block" on later requests; pause_after_compaction keeps recent messages verbatim. Billing: usage.iterations shows the compaction pass separately — docs example: compaction iteration 180,000 in / 3,500 out beside the message iteration's 23,000/1,000 — and "top-level input_tokens and output_tokens do not include compaction iteration usage". Supported: Fable 5, Mythos 5/preview, Opus 4.8/4.7/4.6, Sonnet 4.6.
• Expected savings: no vendor savings number. ESTIMATE on the docs example at Fable 5 list: 180k×$10/M + 3.5k×$50/M = $1.98/pass; afterwards each turn re-sends a ~3.5k summary instead of ~180k history (~98% smaller prefix going forward, before cache effects). Break-even fast for continuing sessions, negative for sessions that end right after. Open 5.6x question: if the summarized history were billed at cache-read rates the pass would cost ~$0.355 — docs are silent (verified absent).
• Evidence tier: T1 for mechanism/billing semantics (live docs); no vendor quality or savings percentages exist for this feature.
• Quality risk: QUALITY-TRADE — the summary is lossy; docs' own mitigation is the memory tool ("nothing critical is lost in the summary"). Cache best practice from docs: cache_control on the compaction block + a separate breakpoint at end of system prompt so the system-prompt cache survives compaction.
• Availability: SDK (beta). Claude Code equivalent: /compact and auto-compact (CLAUDE-CODE-TODAY) — likewise a full billed model call, not free.
• Effort to adopt: minutes on SDK (one edit type + append response blocks)
• Composability: explicitly choreographed with memory tool (6) and context editing (7) as a three-primitive stack; compose with prompt caching per docs.
• Validation protocol: long synthetic session: compare summed usage.iterations cost for (a) compaction, (b) no compaction with client-side history pruning, (c) plain truncation; probe recall of early-session facts after each. Also tests the cache-read billing question empirically.

9. Semantic/RAG index over the repo vs agentic search (grep + file reads)

One-line pitch: Cursor's index gives +12.5% accuracy on codebase questions — but the claim that indexing saves tokens has zero published measurements on either side, and Claude Code/Cline/Letta ship the no-index architecture on purpose.

• Layer: infra (retrieval architecture / harness tooling)
• Mechanism: pro-index: custom embedding model over the codebase; agent gets semantic search + grep (cursor.com/blog/semsearch). Anti-index: Cline — chunking "tears apart" code logic, indexes drift during editing, embedded code copies are a security surface (cline.bot blog, 2025-05); Claude Code ships agentic search only; Letta: plain files + standard tools hit 74.0% on a memory benchmark. Middle path: aider's repo map, graph-ranked, "--map-tokens defaults to 1k" (aider.chat/docs/repomap.html) — structural recall at a fixed ~1k-token standing budget.
• Expected savings: unknown — this is the area's largest evidence gap. Cursor's post measures accuracy only: "on average 12.5% higher accuracy (6.5%–23.5% depending on the model)", code retention +0.3% (+2.6% on 1,000+-file codebases), 2.2% more dissatisfied follow-ups without it; full-page fetch confirms no token or cost comparison anywhere in it. The hypothesis "index → fewer failed greps → fewer tokens" remains unmeasured; so does its converse. Known token costs of adding RAG via MCP: schema overhead (local phase-0: 11 MCP schemas = 1,420 tok loaded vs ~60 deferred via tool search) + retrieved-chunk injection churning the cache prefix.
• Evidence tier: T1 for Cursor's accuracy delta (self-published A/B + private offline eval, no replication); T4 for any token claim in either direction.
• Quality risk: adding RAG is QUALITY-motivated (largest gains on very large repos per Cursor); token impact unknown; index staleness during active editing is Cline's core objection. Staying grep-only is NEUTRAL and free.
• Availability: semantic index: GATEWAY-OR-SELF-HOST via MCP (product feature in Cursor, not Claude Code). Agentic search: CLAUDE-CODE-TODAY. Repo map: shipped in aider.
• Effort to adopt: project (self-hosted embedding MCP server); zero to stay default.
• Composability: a repo-map-style digest can live in CLAUDE.md/auto memory as a bounded standing cost; RAG results injected early compose badly with prompt caching.
• Validation protocol: the would-be first number in existence: 20 fixed codebase questions, grep-only vs MCP embedding server, same model; sum usage tokens per answered question and grade answers. Cheap to run locally; see gaps.

10. Dedicated memory layers (Mem0 / Zep / MemGPT-Letta) — QUALITY-TRADE

One-line pitch: extraction pipelines compress history into a retrieved store — Mem0 claims >90% token savings, but three independent sources show trivial baselines beating these systems on accuracy on the same benchmarks.

• Layer: infra (external memory service)
• Mechanism: MemGPT (arXiv 2310.08560, preprint Oct 2023): OS-style paging between in-context core memory and archival storage. Mem0 (arXiv 2504.19413, vendor preprint): extract salient facts from dialogue into a store (optional graph), retrieve selectively instead of replaying history.
• Expected savings: Mem0 paper (abstract re-): "26% relative improvements... over OpenAI" (66.9% vs 52.9% LLM-as-Judge on LOCOMO, paper body), "91% lower p95 latency" (1.44s vs 17.12s), "saves more than 90% token cost" (~1.8K vs 26K tokens/conversation = 93.1%). Counter-evidence: Letta — filesystem agent on gpt-4o-mini scores 74.0% on LoCoMo vs "Mem0's reported 68.5%... top-performing graph variant"; Letta could not reproduce the MemGPT numbers and "Mem0 did not respond to requests for clarification" (letta.com, re-). ConvoMem (arXiv 2511.10523, 75,336 QA pairs): "simple full-context approaches achieve 70-82%" while "Mem0 achieve only 30-45%... under 150 interactions"; long context "excels for the first 30 conversations, remains viable... up to 150".
• Evidence tier: T3 contested — vendor preprints with multiple independent numbered rebuttals (Letta, ConvoMem, Zep's critique "Lies, Damn Lies, Statistics"). No coding-agent benchmark exists; all numbers are conversational-assistant workloads.
• Quality risk: QUALITY-TRADE today: the token cut is arithmetically real but buys replicated accuracy regressions vs full-context and vs plain files. Treat all vendor memory-layer numbers as adversarial marketing until third-party.
• Availability: GATEWAY-OR-SELF-HOST (Mem0/Zep/Letta services; MemGPT open source). No native Claude Code hook; auto memory (3) covers the core use case file-first.
• Effort to adopt: days (service + MCP integration)
• Composability: competes with, rather than composes with, auto memory and handoff files. Below ~150-conversation histories, ConvoMem's data says you don't need it at all.
• Validation protocol: before adopting: replicate on your own workload — repo-Q&A recall task, candidate memory layer vs files-only baseline (Letta's setup), measuring both accuracy and total tokens. Adopt only if it beats files on BOTH.

11. Semantic response caching (GPTCache / GPT Semantic Cache) — wrong tool for coding agents — QUALITY-TRADE

One-line pitch: serve repeated queries from an embedding-keyed response cache — real on FAQ traffic, evidence-free for coding agents, and a correctness bug when it false-positive hits.

• Layer: infra (gateway/proxy)
• Mechanism: embed incoming query, vector-search prior queries, serve the stored response on similarity hit. Two distinct papers, routinely conflated: GPTCache (ACL Anthology 2023.nlposs-1.24) claims "2-10x" on-hit speedup; GPT Semantic Cache (arXiv 2411.05276, Nov 2024) reports "reduces API calls by up to 68.8% (hit rates 61.6%–68.8%)" with ">97%" positive-hit accuracy — on 8,000 customer-service QA pairs + 2,000 simulated queries.
• Expected savings: up to 68.8% of calls on FAQ-shaped traffic only. For Claude Code-like traffic: ~zero expected — prompts embed file contents, diffs, session state; superficially similar queries ("fix the test") demand different answers. The local phase-0 mix (92.83% of heavy-session input = prefix cache reads) shows coding-agent repetition lives in the PREFIX, which Anthropic prompt caching already prices at 0.1x — the whole-response repetition this technique needs does not exist in the workload.
• Evidence tier: T2 for the FAQ numbers (workshop paper + arXiv preprint with experiments); T4 for any coding-agent application — no study exists.
• Quality risk: RISKY→QUALITY-TRADE: false-positive hits silently return stale/foreign answers; threshold tuning trades hit rate against wrongness. NEUTRAL only for genuinely identical sub-tasks behind a gateway (e.g., repeated lint-fix prompts across CI), scoped per repo+commit.
• Availability: GATEWAY-OR-SELF-HOST
• Effort to adopt: days (proxy + embedding store)
• Composability: orthogonal layer to prompt caching; composes badly with per-session state. Anti-synergy with everything cache-prefix-based.
• Validation protocol: shadow mode: replay a week of real prompts through the cache without serving hits; measure would-be hit rate and manually audit 50 would-be hits for correctness. Predicted outcome for coding traffic: hit rate near zero, making the audit moot.

Claims to kill

Open gaps (ranked by local fillability)

1. RAG vs agentic-search token cost — no number exists anywhere; 20-question local A/B would be the first (technique 9 protocol).
2. Auto memory net effect — startup tax bounded ($0.12–$1.40/day ESTIMATE), savings unmeasured (technique 3 protocol).
3. Handoff file vs /resume vs auto-compact — three competing continuation mechanisms, zero comparative data, including from Anthropic (technique 4 protocol).
4. Context-editing cache-invalidation tax — acknowledged qualitatively in docs, priced nowhere; local break-even formula needs empirical check (technique 7 protocol).
5. Whether the API compaction pass bills previously-cached history at cache-read rates — a 5.6x cost question, docs silent (technique 8 protocol).
6. MEMORY.md cache placement — if the auto-memory block churns the prefix per session it costs 1.25–2x writes, changing technique 3's arithmetic.
7. All memory-layer benchmarks are conversational; no coding-agent memory benchmark exists — every technique-10 number is an out-of-domain transfer.

Verification ledger