OpenAI is rolling out its answer to Anthropic's Mythos — the GPT-5.6 series. Sol is the flagship, Terra and Luna are smaller and faster.
What the models do
Terra is promised at roughly GPT-5.5 level, but at half the price. Sol was trained with a focus on agentic coding, biology/genomics, and cybersecurity — specialized profiles that previous GPT models didn't have.
New modes
Two new modes are coming: max reasoning effort for deeper reasoning, and ultra mode, where the model uses subagents(!) for complex tasks. Effectively, one model becomes an orchestrator for a fleet of agents.
Safety and access
The model is significantly more capable, so OpenAI is doing a staged rollout with stricter safeguards. By their own assessment, Sol doesn't cross the Cyber Critical threshold — their internal risk classification for cybersecurity capabilities.
Access is currently a limited preview in API and Codex for select trusted partners.
Pricing per 1M tokens
- **Sol**: $5 input / $30 output
- **Terra**: $2.5 / $15
- **Luna**: $1 / $6
Sol on Cerebras (maker of wafer-scale AI inference chips) is planned for July at up to 750 tokens/sec — limited access there too at first.