OpenAI Gave Cache Misses Nine Reason Codes. Its Own Coding Agent Still Trips One of Them.
OpenAI's Prompt Cache Diagnostics, GA since 8 September, label every Responses API cache miss with one of nine reasons. One of them, reasoning_effort_changed, already has a fix in GPT-6 Astra's configuration_update, and the Codex CLI still changes effort the old way. On Astra a cache write costs $12.50 per million tokens against $1 for a read, so a miss caused by your harness is now a surcharge, not a lost discount.
Sonar Instrumented Its Own Coding Agent. One Unnecessary File Read Got Billed 470 Times.
Sonar instrumented 18 pull requests written by a coding agent on its own codebase and published the traces on 1 September. One 800-line PR was billed 156 million tokens for 289,000 tokens of output. 152.8 million of those were cache reads, which means the cost of a file read is set by how early in the session the agent made it.
US Models Fell From 70 to 30 Percent of OpenRouter Traffic in a Year
American models fell from 70 percent of OpenRouter token traffic to about 30 percent in a year, while Chinese open-weight models took the rest. It is a cost story, not a quality story, and real companies are already routing production workloads across the 60 to 90 percent price gap.