The Disaggregated KV Cache — Four Techniques to Cut Your Token Bill This Sprint
Why Now
Per-token prices fell 80% since 2023 (GPT-4 class: $30/M → $0.40/M). The thing that number doesn't tell you is that agentic workloads burn 5-30x more tokens per task, so the discount gets eaten before it reaches your bill. Stanford's measurement: ~62% of every agent call is repeated context — system prompts, tool definitions, documents. Uber exhausted its entire 2026 AI budget in 4 months after a Claude Code rollout. Gartner forecasts 40% of agent projects cancelled by 2027 on cost overruns. The fix isn't a cheaper model. It's not recomputing KV cache you already have.
The Technique Stack
| Technique | What It Does | Reported Gain | Deploy Complexity |
|---|---|---|---|
| LMCache (disaggregated) | Separate process + shared GPU memory, multi-tier GPU/CPU/SSD/remote checked in parallel | 14x TTFT, 4x decode (H200 + Qwen3-235B, 50 concurrent) | Config-level; integrates vLLM/SGLang/TensorRT-LLM |
| CacheBlend (EuroSys Best Paper) | Selective recomputation of cross-document attention tokens only | 2-4x multi-document RAG, zero quality loss claimed | Inference-time bolt-on |
| Context Pruning Filter | Small LLM gates relevance between retriever and generator | 68% chunk reduction, 96% recall | Days; cross-encoder or small model |
| Judge-Actor Split | Critic verifier in agent loop catches failures early | Up to 1.72x fewer tokens | Days; architectural pattern |
The architectural insight behind LMCache: standard prefix caching requires exact byte-for-byte match and breaks on multi-document RAG, changing doc order, and growing history. Those are the exact patterns production agents run, which is why the lab win rarely survives contact with real traffic. Alibaba's data shows 10% of KV blocks serve 77% of hits, so effective reuse is heavily skewed and a small hot set does most of the work. LMCache pulls cache into a separate process with graceful failure: cache survives engine crash; engine downgrades to no-cache if LMCache dies.
Cheaper tokens didn't save you — agent volume ate the discount; the win is in the cache you're throwing away 15 TB of per GPU per day.
Cross-Source Validation
Tencent independently shipped fused FP8 MoE kernels into vLLM main alongside Hy3, reporting up to 2.95x on mixed-length decode and ~24% TTFT / ~17% TPOT vs default backends. DSpark added confidence-driven speculative decoding to SGLang. The sources converge on one thesis: this quarter's lever isn't a smarter model, it's cheaper orchestration around the model you have.
Caveat: LMCache's 14x/4x numbers come from a single config (H200, Qwen3-235B, 50 concurrent) with no ablations. The pruning filter reports no eval set size, baseline, or filter model. Reproduce on your own traffic.
What to do
Instrument your current inference stack to measure actual prefix cache hit rate and redundant-token ratio per request
Deploy LMCache alongside existing vLLM/SGLang on staging this sprint, replaying production traffic; measure TTFT and decode throughput delta
Insert a small model or cross-encoder as a relevance filter between retriever and generator; measure chunk-reduction vs. recall on your gold eval set
Prototype a judge-actor critic stage in your highest-volume agentic pipeline and A/B token usage against current baseline