🚀 AI agents can now handle even longer, harder coding and science work with less babysitting. Title: Introducing Claude Fable 5.1 and Claude Mythos 5.1 URL: 📊 Overview Anthropic released two new models built on the same underlying model with different safety configurations: Claude Fable 5.1 (general availability) and Claude Mythos 5.1 (restricted, vetted access). 🎯 Problem Solved The release targets three challenges: maintaining reasoning quality during long unattended runs, stronger self-verification in complex workflows, and reducing safety false positives that hurt legitimate users. 🔬 Methodology and Approach Mythos 5.1 is limited to vetted professionals through the Cyber Verification Program and Life Sciences Verification Program, while Fable 5.1 ships broadly as the standard model. New Enterprise Frontier Safeguards add zero data retention, and new anti-distillation protections block illicit capability extraction. 📈 Results Agentic scientific research benchmark scores jumped from 24.7% to 52.6%, and agentic coding scores from 42.0% to 55.8%. The model designed protein binders with 10x the affinity of competition winners and produced a new high-resolution Venus elevation map. Cache read pricing dropped 75%. #ClaudeFable# #AIAgents#

Claude Opus 5.5 is now available as the Standard effort level in Perplexity Computer. On our WANDR benchmark, it scored 0.610 at $4.13 per task, slightly outperforming Claude Fable 5.1 while costing 67.6% less per task.

Claude Opus 5.5 (max) is a top performer in agentic knowledge work. It leads AA-Briefcase v1.1 at 1,822 Elo (+143 over Fable 5.1) and GDPval-AA v2.1 at 1,846 Elo (+111 over Claude Fable 5.1, +138 over Claude Opus 5). On AA-Briefcase it leads across analytical quality and presentation sub-scores, and sits just behind Fable 5.1 for rubric-based scoring

Claude Fable 5.2 @claudeai @ClaudeDevs you guys seriously cooked with this model no assets , no mcp , no inspiration , fully coded in JS nothing else see my cute claude mascot and this world everyone is drawn in code

Claude Fable 5.1 is now live on LobeHub, with a massive jump in agentic performance. 🔥 → 52.6% on Terminal Bench Science, more than 2× Fable 5 → 55.8% on Terminal Bench 4.0, up from 42.0% → Stronger across coding, research, computer use, and business workflows → Up to 45% lower cost on highly agentic workloads Built for long running tasks, deep research, and complex agent workflows. Try Claude Fable 5.1 on LobeHub today.

Claude Fable 5.1 is now available in our model picker! We're starting off with the same use cases as Fable 5 - extremely long, multi-step tasks that require deep reasoning - and we're increasingly pushing the model to complete tasks that can run unattended. Try it today in Cosmos:

Claude Fable 5.1 is now available in Glean, alongside 40+ open and frontier models. Our judges preferred Fable 5.1's answers roughly 2:1 over Fable 5 across everyday knowledge questions, high-intent research, and drafting and artifact work, with improved response grounding.  Watch @claudeai Fable 5.1 plan an architecture redesign of a complex software project.