Claude.ai system prompt has ballooned to 138k tokens, up from 24k
frubberism · reddit · 2026-09-03
A user discovered and published Fable 5.1's full Claude.ai system prompt: it now weighs in at 138k tokens, versus just 24k back in May 2025 under Claude 3.7 Sonnet — nearly a 6x increase in about a year. The full prompt is on a GitHub system-prompt-leaks repo, offering a rare look at how Anthropic constrains model behavior via prompting.
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