GPT-6 Astra vs GPT-6.1 Sol vs Gemini 4 Argon vs Claude Fable 5.1: Which Frontier Model Fits Which Job
MarkTechPost Asif Razzaq
Four frontier models landed in 30 days, and the cheapest one isn’t always the best deal. Sol is the default pick; Astra still wins the hardest jobs.
Based on reporting by MarkTechPost, Asif Razzaq — read the original for the full story.
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Anthropic, OpenAI and Google DeepMind all pushed out frontier-class models within a single month, but the launch race hides a quieter truth: the best model depends heavily on the job. Claude Fable 5.1 came first on September 1, GPT-6 Astra followed on September 3, and GPT-6.1 Sol plus Gemini 4 Argon arrived at the end of September. OpenAI also pulled GPT-6.1 Astra on September 28 after internal scope and authorization tests went sideways, leaving GPT-6 Astra as its top model for now.
On paper, the pricing spread is wide. Astra and Fable 5.1 both list at $10 input and $50 output per million tokens. Sol and Argon sit at one-fifth of that, though Argon’s $2 and $10 intro price later doubles. Cached input is where agents start caring, because they resend the same context again and again. Astra reads cache at $1.00 per million tokens; Fable 5.1 is $0.25; Sol and Argon are $0.10, at least for now.
The benchmarks don’t crown a single winner. Google’s comparison table has Argon ahead on long-horizon software work, with 77.9% on DeepSWE v1.1, while Astra leads FrontierSWE v2 at 65.5% and OSWorld-2.0 at 72.6%. OpenAI says Sol lands close to Astra on its own tests, including DeepSWE v1.1 and an offline OSWorld 2.0 set, while costing much less. And on Artificial Analysis’ numbers, Fable 5.1 and Argon can look stronger than Astra on raw intelligence measures, even if the margins move around depending on the benchmark.
That leaves a messy but practical split. Sol looks like the default for teams that want volume without burning cash. Astra is the safer bet when the work is harder: computer use, frontier engineering, hard research. Argon is the odd one out, with a 1M output cap and access locked to Fairwind cyber defenders. Fable 5.1 starts to make sense when cache reuse matters, because its cached input is a quarter of Astra’s. The headline lesson is boring in the best way: the cheapest sticker price does not mean the cheapest agent.
My take — AI-written commentary, not fact-checked reporting
This is the part model vendors hate: the best model is usually the one that survives the bill. Frontier benchmarks are useful, but they’re also a nice way to sell a very expensive spreadsheet. Open models keep getting boxed out while closed vendors quietly turn access rules, cache pricing and safety gates into the real product.
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