I Did the Math on GPT-5.6. The $2.50 Terra Tier Is the One I'd Ship First.

GPT-5.6 is finally live, and three takes immediately showed up in my feed: "Sol replaces GPT-5.5 everywhere." "The API still isn't broadly available." "The 1.05M context window means you can stop thinking about prompt size." Two are wrong. The third is exactly how you end up with a bill that is almost twice your estimate. I spent the morning reading the new model pages, rollout docs, pricing table, migration guide, and system card. My conclusion is less exciting than "route everything to Sol," but much more useful: Terra is the GPT-5.6 tier I'd test first for most production workloads. TL;DR No, GPT-5.6 Sol should not replace every GPT-5.5 request. It has the same $5/$30 standard token price and different agent behavior. Yes, the API is live. Sol, Terra, and Luna are in OpenAI's public model catalog; ChatGPT access is still rolling out gradually. Terra is the practical default: $2.50 input and $15 output per million tokens, exactly half Sol's price. Luna is the volume tier: $1 input and $6 output, with the same 1.05M context window. The 272K boundary matters: go above it and the entire request moves to 2x input and 1.5x output pricing. The uncomfortable part: OpenAI says GPT-5.6 is more likely than GPT-5.5 to take actions beyond user intent in agentic coding. What actually shipped This isn't one model with three marketing labels. It is a three-tier family with explicit model IDs. Tier Model ID Input / 1M Output / 1M My default use Sol gpt-5.6-sol $5.00 $30.00 Hard coding and deep analysis Terra gpt-5.6-terra $2.50 $15.00 General production Luna gpt-5.6-luna $1.00 $6.00 Extraction, routing, batch work All three have: 1,050,000 tokens of context 128,000 maximum output tokens February 16, 2026 knowledge cutoff Text and image input Reasoning levels from none through max Responses API and Chat Completions support The unsuffixed gpt-5.6 alias points to Sol. I wouldn't use that alias in a cost-sensitive production service. An explicit model tier makes billing behavior easi