Claude 5 changed the rules of context engineering: over 80% of Claude Code’s system prompt is gone

🚀 Claude 5 changed the rules of context engineering

The old golden rule of context engineering

Until a few months ago the golden rule was clear:

“Put ALL the rules in the context, always. Otherwise the model won’t see them.”

Endless system prompts, CLAUDE.md files packed with instructions, examples on top of examples, repetitions...

Over 80% of Claude Code’s system prompt removed

We literally had to “rein in” the model to avoid disasters. With the new generation of Claude models (Opus 5, Fable 5…) Anthropic did something wild:

they removed over 80% of Claude Code’s system prompt → zero performance loss on coding evaluations.

The figure comes from the post “The new rules of context engineering for Claude 5 generation models”, published by Anthropic on July 24, 2026 and written by Thariq Shihipar.

The new paradigm: judgment, progressive disclosure, expressive tools

The new paradigm is completely different:

Before → Give rigid rules
Now → Let it use its judgment

Before → Put everything upfront
Now → Progressive disclosure (load only what’s needed, when it’s needed)

Before → Give detailed examples
Now → Design clear interfaces and expressive tools

In practice: you no longer need to force every piece of information into the context.

You need to give the model easy, smart ways to find what it needs on its own (on-demand skills, deferred tools, file trees, auto-memory, rich references…).

The model has become good enough that it no longer needs to be “controlled” obsessively.

It needs room and good entry points.

The /doctor command in Claude Code

💡 Practical tip: if you use Claude Code, just type /doctor.
It automatically analyzes and “trims” skills and CLAUDE.md, applying exactly these new best practices.

The lesson for anyone building agents

This is an important lesson not just for Claude Code users, but for anyone building agents or systems on the 5 line of Anthropic’s models.

Fewer rules. More trust. Better context design.

Are you already applying this approach?