OpenAI Ships GPT-5.6 Family to the Public and Claims the Top Coding Benchmark

OpenAI released GPT-5.6 as a three-model family: Sol at the top, Terra in the middle, and Luna as the low-cost tier. The central claim is about agentic coding. OpenAI and early testers report that a new Sol Ultra mode, which spawns subagents to run parts of a complex task in parallel, reached 91.9 percent on Terminal-Bench 2.1, with base Sol at 88.8 percent. Both figures sit above Anthropic's Mythos 5 at 88.0 percent and Fable 5 at 84.3 percent.

The skeptical reading matters here. Terminal-Bench is an agentic, terminal-driven evaluation whose scores shift with random seeds, harness configuration, tool timeouts, and retry policy. A 0.8-point gap between base Sol and Mythos 5 falls within the range where two runs of the same model routinely disagree, so the practical claim is parity at the top, not a decisive lead. Ultra mode's larger margin comes from using more inference compute, not from a cheaper capability.

Pricing is where the release is more concrete. Sol lists at $5 per million input tokens and $30 output, Terra at $2.50 and $15, and Luna at $1 and $6, positioning the family below Anthropic's Fable 5 on cost for comparable coding work. OpenAI also confirmed that GPT-5.6 is now the preferred model in Microsoft 365 Copilot, placing the model directly inside Word, Excel, and PowerPoint for enterprise users. The Russian-language developer channel AI ML Big Data separately flagged Sol's record Terminal-Bench number and strong first-tester coding reports.