Claude 5 system prompts reportedly reach 135K characters as context engineering shifts
Roger_M_Taylor · x · 2026-07-26
A post highlights just how large Claude 5 system prompts have become: Opus 4.8 is said to use a 130K-character prompt, and Opus 5 around 135K.
The linked article argues that, for Claude 5 models, prompt design has shifted toward context engineering: the author says they removed about 80% of the Claude Code system prompt and learned better ways to write system prompts, skills, and Claude.MD files.
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