Prompt caching cut this generation pipeline’s cost more than switching to a cheaper model
Illustrious-Bug2105 · reddit · 2026-07-26
Prompt caching cut this user's generation pipeline bill more than switching to a cheaper model.
The post explains why a large immutable prefix plus a small variable suffix is ideal for provider-side caching, and details the main failure modes:
- Cache hits are order-sensitive and require byte-identical text at the start of the prompt.
- Volatile fields like timestamps can silently break cache reuse.
- Cache entries expire quickly, so bursty workloads may see little benefit.
- Designing prompts for caching changes the whole prompt-writing workflow.
The author asks when caching beats simply using a smaller model, especially for high-volume generation or agent loops.
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