GPT-6 vs Claude Opus 5.5 vs Grok 4.7: which AI model should you actually pick?

September's biggest model week ended with the leaders nearly tied, so price per task — not benchmarks — is now the smart way to choose which AI model to use.

September packed a year's worth of AI model launches into a few weeks: Grok 4.7 on September 21, GPT-6 Sol and Luna plus Claude Opus 5.5 on September 22, Claude Sonnet 5.5 on September 28, and GPT-6.1 Sol at DevDay on September 29. Here is the insight most coverage skips: benchmark gaps between the leaders are now within noise, so ‘which is best?’ is the wrong question. The real difference is price per task.

OpenAI's GPT-6 Luna costs about $0.10 per million input tokens and $0.50 for output; Claude Opus 5.5 runs $4 and $20; Astra-class models run roughly $10 and $50. Use a simple rule: the cheap, efficient tier for bulk or focused tasks, and the frontier model only for genuinely hard work that actually needs it. Before committing your whole workflow, shadow-test the cheaper model on your own real task — one benchmark point can easily be noise, not superiority.