Prompt Caching at Scale: How SpiderGate Reduces Redundant LLM Calls by 40%
Every LLM call costs money and time. And in production agent systems, a staggering number of those calls are redundant — identical or near-identical prompts sent minutes apart by different agents or the same agent in different sessions.
The Redundancy Problem
In a typical multi-agent deployment:
System prompts are identical across every request for a given agent type
Common queries like "summarize this document" hit the same model with similar inputs
Retry storms resend the exact same prompt after transient failures
Parallel agents independently generate the same analysis
Our telemetry shows that 30-50% of LLM calls in production are semantically redundant.
How Prompt Caching Works
Exact Match Cache
For identical prompts (same system prompt + user message + parameters), SpiderGate maintains a hash-based cache with configurable TTL.
Semantic Cache
For near-identical prompts, SpiderGate computes embedding similarity. If a cached response exists with > 0.95 similarity score, it's served directly.
Cache Layers
| Layer | Latency | Hit Rate | Use Case | |-------|---------|----------|----------| | L1: In-Memory | < 1ms | ~15% | Hot prompts within single node | | L2: Distributed | < 5ms | ~25% | Shared across gateway cluster | | L3: Persistent | < 20ms | ~10% | Long-term semantic matches |
Cache Invalidation
The hardest problem in computer science, handled pragmatically:
TTL-based — cached responses expire after configurable duration
Model-versioned — cache invalidates when provider updates model weights
Manual purge — API endpoint to clear cache for specific agents or prompts
Confidence-gated — only cache responses above a quality threshold
Cost Impact
For a team running 50 agents with ~100K daily LLM calls:
Before caching: $850/day average spend
After caching: $510/day average spend
Savings: ~40% reduction, ~$10K/month
Latency Impact
Cached responses are served in < 5ms vs. 500-2000ms for live LLM calls:
P50 latency drops from 800ms to 200ms
P99 latency drops from 3s to 900ms
Prompt caching requires SpiderGate V2.1+. Enable per-agent via the routing configuration.