Anthropic Cuts 80% of Claude Code's System Prompt — Fable 5 Models 'Want Smaller System Prompts'
Anthropic has cut 80% of Claude Code's system prompt because Fable 5 (Mythos class) models perform better with fewer instructions — a shift that redefines prompt engineering.
Anthropic Cuts 80% of Claude Code's System Prompt — Fable 5 Models 'Want Smaller Prompts'
Anthropic has cut 80 percent of the system prompt for Claude Code. Tariq Shihipar, a member of technical staff at Anthropic, describes a fundamental shift in how AI models are steered, tied to the new Fable 5 models, also known as the Mythos class. More instructions and more examples no longer automatically lead to better results.
'Most recently we found this new class of models want a smaller system prompt,' Shihipar says, and examples 'tend to constrain it because it's actually more imaginative than the examples we give it.' Instead of hard rules like 'do not do this,' Anthropic now tries to steer Fable models through context.
What Does This Mean?
This shift has major implications for how developers interact with AI coding tools. For Georgian developers using Claude Code, this means less time crafting perfect prompts and more freedom to let the model interpret tasks creatively. This development fundamentally changes prompt engineering as a discipline.