I've heard they actually cache the full Claude Code system prompt on their servers and this saves them a lot of money. Maybe they cache the MCP tools you use and other things. If another harness like Opencode changes that prompt or adds significantly to it, that could increase costs for them.

What I don't understand is why start this game of cat and mouse? Just look at Youtube and YT-DLP. YT-DLP, and the dozens of apps that use it, basically use Youtube's unofficial web API and it still works even after Youtube constantly patches their end. Though now, YT-DLP has to use a makeshift JS interpreter and maybe even spawn Chromium down the line.