Last month's Anthropic bill hit $312. Sixty percent of it traced back to a single 6-hour window when I was doing an in-place Vectorize index rebuild.
Here's the part I didn't expect: the rebuild didn't throw errors. Queries returned results, scores just quietly dropped from 0.78 to 0.61. My agent interpreted that as "no relevant docs found" and fell back to Claude directly — 2,880 times over six hours. At ~5K input tokens per query on Sonnet, that's $43 in LLM fallback costs from what I thought was a routine maintenance task.
The fix was a Blue/Green swap. I spun up ads-insights-v2 alongside the existing index, rebuilt all 180K vectors into it using 256-token chunks (down from 512), validated against a 20-query golden set, then flipped one environment variable:
wrangler deploy --var VECTORIZE_INDEX_NAME:ads-insights-v2
Enter fullscreen mode
