LLM cost per request tripled because retries and prompt bloat, not traffic

Lance_Saul_85 · reddit · 2026-07-21

A production team found its cost per request tripled even though traffic stayed flat — and the culprit was retries plus prompt bloat, not demand.

• After instrumentation, they discovered a timeout retry path that could fire three full-price calls for one request in some failure modes.
• They also found their shared system prompt had silently grown to nearly 4k tokens over months as people kept appending guardrails without removing older ones.
• The retry bug is fixed; the remaining problem is organizational: nobody wants to delete another person’s prompt line, so the team is asking for a more boring, automatic process to keep the prompt under control.
• The post is a practical reminder that LLM spend often comes from hidden engineering debt, not just usage growth.

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