GPT-5.6
OpenAI current flagship — Sol/Terra/Luna tiers, 1.05M context
Verdict
GA since July 2026 and now the OpenAI default. Sol is the flagship tier (88.8%, 91.9% on Sol Ultra), Terra a balanced mid-tier at roughly half the cost, Luna the cheap high-volume option — same 1.05M-token context and 128K output across all three. Ahead of GPT-5.5 and Claude Opus 4.8 on OpenAI's own benchmark, still behind the gated Claude Mythos 5. Terra is the sane default for most agentic and coding work; reach for Sol only when you are actually bottlenecked on quality.
Other Text Generation & Reasoning
- GPT-5Superseded
OpenAI's previous flagship — superseded by GPT-5.6
- GPT-5 miniProduction
OpenAI's cost-efficient GPT-5-tier model — most of the quality at a fraction of the cost
- GPT-4oProduction
OpenAI previous-gen multimodal model — text, vision, audio
- GPT-4o miniStable
OpenAI's previous-gen cost-efficient model — superseded by GPT-5 mini
- GPT-OSS 120BStable
OpenAI's first open-weight model — 120B params, fully downloadable
- Claude Fable 5Production
Anthropic's most intelligent generally available model — Mythos-class reasoning