PulseAugur
EN
LIVE 13:56:30

Anthropic's Fable 5.1 model expands system prompt to 138k tokens

By PulseAugur Editorial · [1 sources] ·

The system prompt for Anthropic's Fable 5.1 model has been expanded to 138,000 tokens. This represents a significant increase from the 24,000 tokens available in May 2025 with the Claude 3.7 Sonnet model. The full system prompt has been made available through a GitHub repository. AI

IMPACT Increased system prompt size may allow for more complex instructions and context handling in AI interactions.

RANK_REASON The item details a technical specification change (system prompt size) for an AI model, which falls under research. [lever_c_demoted from research: ic=1 ai=1.0]

Read on r/ClaudeAI →

AI-generated summary · Google Gemini · from 1 sources. How we write summaries →

Anthropic's Fable 5.1 model expands system prompt to 138k tokens

How we ranked this

Signal score
3 / 100
Composite score across the factors below. Higher = stronger signal that this story matters right now.
Newsworthiness bucket
Tool
The item details a technical specification change (system prompt size) for an AI model, which falls under research. [lever_c_demoted from research: ic=1 ai=1.0]
Source corroboration
Single-source cluster
Only one publisher covered this so far. Single-source stories can still rank when the publisher is high-authority, but they lack cross-source corroboration.
Topics
model release
Editorial topic classification. Feeds into how the story surfaces on /topic/<slug> hub pages and into the per-entity coverage mix.
AI-industry relevance
High
Clearly on-topic for AI-industry coverage.
Story freshness
Breaking (< 6h)
Fresh story with cross-source coverage still developing. Ranking may shift as more sources report.

Full methodology in our editorial standards.

COVERAGE [1]

  1. r/ClaudeAI TIER_2 English(EN) · /u/frubberism ·

    Fable 5.1's Claude.ai System Prompt is now 138k tokens (up from 24k in May 2025 when we had Claude 3.7 Sonnet)

    <table> <tr><td> <a href="https://www.reddit.com/r/ClaudeAI/comments/1w61jq4/fable_51s_claudeai_system_prompt_is_now_138k/"> <img alt="Fable 5.1's Claude.ai System Prompt is now 138k tokens (up from 24k in May 2025 when we had Claude 3.7 Sonnet)" src="https://preview.redd.it/8u36…

RELATED ENTITIES

RELATED TOPICS