A comparative analysis of gpt-6 astra, GPT-6.1 sol, gemini 4 argon, and claude fable 5.1 in the frontier AI landscape

In late September 2026, Anthropic, OpenAI, and Google DeepMind launched four frontier-class AI models within a month. GPT-6 Astra was released on September 3, followed by GPT-6.1 Sol and Gemini 4 Argon in late September. Claude Fable 5.1 debuted on September 1. OpenAI later canceled GPT-6.1 Astra on September 28 due to internal issues, leaving GPT-6 Astra as its top model. Pricing and performance vary across models. GPT-6 Astra and Fable 5.1 share a $10 input and $50 output list price, while Sol and Argon are priced at one-fifth. Argon’s introductory pricing doubles later. Astra’s cached-input rate is four times Fable 5.1’s and ten times Sol’s. Argon’s 1M output cap stands out, while others limit responses to 128K tokens. Performance metrics show no clear winner. Argon leads in knowledge work and coding, while Astra excels in software engineering. Artificial Analysis reports Astra scores 61 on the Intelligence Index, with Fable 5.1 slightly higher. Cost per task varies, with Fable 5.1 at $9.18 versus Astra’s $4.72, driven by token usage. Access restrictions further define use cases, with Argon limited to Fairwind cyber defenders and Astra’s advanced capabilities behind OpenAI’s Daybreak program.