How GPT-5.6 fuses frontier intelligence with frontier efficiency

OpenAI's GPT-5.6 model family, including Sol, Terra, and Luna, balances capability and cost. GPT-5.6 Sol outperforms Claude Fable 5 on the Artificial Analysis Coding Agent Index at less than half the cost, while Terra matches GPT-5.5 intelligence at half the price, and Luna is 80% cheaper than Sol. These efficiencies stem from significant optimizations across models, inference, and the agentic harness. GPT-5.6 Sol also optimized its own forward pass and autonomously rewrote production kernels in Triton and Gluon, reducing serving costs by 20%.