OpenAI's Prompt Cache Diagnostics tool is now GA in the Responses API. It adds comparison_response_id and a reason field that explain cache misses—and breaks silently if your AI gateway strips prompt_cache_options.
Anthropic's September 1 API release added three beta controls — per-message effort, turn-scoped system messages, and mid-conversation tool changes — that let operators adjust compute intensity and tool sets in long agentic sessions without invalidating the cache prefix.
Claude Code 2.1.237 silently fixed a bug that invalidated prompt caching for every session routed through a custom base URL. If you've been routing Claude Code through a gateway, you've been paying full context-window cost on every turn since at least 2.1.229.
Anthropic's mid-conversation system messages dropped their beta header on July 15 across the API, Bedrock, and Vertex AI. If your gateway proxies Claude without forwarding role:system turns in the messages array, your agentic sessions are already silently broken.
Claude Code 2.1.211 fixes a prompt-caching billing regression that silently billed the trailing system context block as fresh input tokens on every request across Bedrock, Vertex AI, Mantle, and Foundry. Gateway operators have overcharges to investigate.
OpenAI now defaults eligible GPT-5 prompt cache retention to 24h for non-ZDR organizations. Learn how GPT-5.5, prompt_cache_key, and gateway routing choices affect API cost and data policy.
