In early September 2026, Anthropic launched Claude Fable 5.1 and Mythos 5.1 models. Fable 5.1 is designed for general programming, knowledge-based tasks, and agent-based applications. Its benchmark scores for scientific agents doubled, the cost of agents was reduced by up to 45%, and cache prices were significantly lowered. Mythos 5.1 focuses on advanced professional scenarios such as network security and life sciences. This upgrade aims to lower the barriers to use and improve research efficiency through technical optimization. In terms of performance, Fable 5.1 demonstrated strong autonomous operation capabilities, achieving 38 hours of continuous operation without human intervention. It can dynamically identify experimental anomalies, start multiple tasks concurrently, and adjust strategies based on environmental changes. Meanwhile, Google’s Gemini 3.8 Flash series, released during the same period, improved software engineering and agent workflow performance without increasing prices. The competition among global AI manufacturers in programming capabilities has become even more intense.
Claude Fable 5.1 and Mythos 5.1 were released in early September 2026. Research scores doubled, and the Agent…
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2026-09-01
Anthropic released Claude Fable 5.1 and Mythos…
On September 1st, Anthropic launched Claude Fable 5.1 for programming and knowledge work, and Mythos 5.1 for professional scenarios.
2026-09-03
Details of the release: 38 hours of development and model customization
According to Leifeng Network, Anthropic released Fable 5.1 and Mythos 5.1 after 38 hours of intensive development. Both are different branches of the same underlying model.
2026-09-04
72-hour AI competition: Programming remains the focus
According to Titan Media, global manufacturers released flagship models intensively within three days in early September. The release of Claude Fable 5.1 and Mythos 5.1 sparked unprecedented competition.
2026-09-08
Performance tests: Research scores doubled, costs significantly reduced
According to稀土掘金, the benchmark scores of Fable 5.1’s research agents doubled, with the Agent cost reduced by up to 45% and cache price by 75%.
# Disassembly of Claude 5.1: Behind the 38-hour non-sleep period, Anthropic is ending “Model Theory”
## Key Event
Anthropic recently updated Claude 5.1, introducing Fable 5.1 and Mythos 5.1 in one go. These two names may seem different, but they actually represent different branches of the same underlying model: Fable focuses on general coding, knowledge-based work, and agent tasks, while Mythos is designed for verified scenarios in network security and life sciences research, allowing for deeper tool invocation and specialized tasks.
## Key Breakthrough: 38 Hours of Unattended Operation
In a test conducted by Ramp, Fable 5.1 ran unattended for 38 hours, identifying label artifacts during the experiment, reprocessing data, starting 6 sets of experiments in parallel, and continuing to modify subsequent plans based on the results. This process did not follow the initial plan mechanically but adjusted according to environmental changes…
# 72-hour AI competition: Programming remains the crown jewel
## 72-hour AI model competition: Programming skills remain the focus of competition
Within three days at the beginning of September, global AI companies released their flagship models, sparking an unprecedented “arms race”.
**On September 1st**, Anthropic launched Claude Fable 5.1 and Claude Mythos 5.1, targeting “the strongest models for programming and knowledge-based tasks”, with programming performance doubling directly. Claude Fable 5.1 is available to ordinary users, while Claude Mythos 5.1 is available to enterprises through Trusted Access Programs.
**On September 2nd**, Google released Gemini 3.8 Flash and Gemini 3.8 Flash Cyber, improving software engineering and Agent workflow performance without increasing prices. The Gemini Flash series is now closer to version 3.7…