Claude Code marks its messages with caching points. As a result, almost every request consists of a long cached prefix and a new, truncated final part. Based on practical experience with Opus 5.5, reading from the cache appears to cost $0.20 per million tokens, accounting for about 92–95% of the tokens charged for prompts. Meanwhile, a five-minute cache entry costs $5, which is 25 times more expensive than reading from the cache. When an agent needs to run a build or a longer training cycle, they face the problem of the cache expiring. The next request then has to write the prefix to the cache again. We saw this 33 times in a cycle of 89-task runs without compression. As a result, 927,000 tokens were rewritten, which is approximately one-third of the volume billed in full.