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The new GPT-5.6 family: Luna, Terra, Sol

L4 · DeveloperModels & ReleasesSimon Willison's Blog· 7/9/2026

Provides critical analysis of pricing, benchmarks, and new API features for developers integrating the next major OpenAI model.

AI Summary

OpenAI has released the GPT-5.6 model family in three sizes—Luna, Terra, and Sol—with pricing and performance benchmarks positioning them against Claude's Fable 5, particularly in long-running agentic workflows. The post analyzes the new models' efficiency claims, provides developer notes on pricing and context windows, and discusses new API features like programmatic tool calling and multi-agent capabilities.

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