Yep, sounds like the Opus I despise and the reason I dropped Claude Code. It reads like it doesn't want to be understood.

I compared the Claude Opus 4.8 and 5 system prompts, as well as the Claude Code Opus 4.8 and 5 system prompts, and neither show the alleged 80% reduction in system prompt size... Is the Claude Code system prompt leak incorrect? Do I not know what 80% looks like? Why such a large lie (so it seems)?

Claude Code prompt leaks: https://github.com/asgeirtj/system_prompts_leaks/tree/main/A...

Best source I can find about the 80% reduction: https://x.com/trq212/status/2080710971228918066

afaiu the 80% reduction is about the Claude Code system prompt

maybe someone has a diff of this (would be interesting!)

unfortunately Anthropic only publishes the system prompts of Claude app/web

Right, but there are (allegedly) leaks of the Claude Code system prompts (which I linked to), and the 80% reduction is not seen there either.

It's in Claude Code, not the website.