OPENAI CONFIRMS GPT-5.6 DETAILS: TERRA CUTS GPT-5.5 COSTS IN HALF AND A PRICE WAR WITH CLAUDE SONNET 5 IS ON OpenAI has confirmed the full technical details of its GPT-5.6 preview, and the most significant number is not a benchmark score. It is a price. GPT-5.6 Terra, the mid-tier model in the new family, delivers performance competitive with GPT-5.5 at approximately half the cost. That puts Terra in direct competition with Claude Sonnet 5, which Anthropic launched at introductory pricing of two dollars per million input tokens through August 31. When GPT-5.6 hits general availability, expected within the next two weeks, the frontier AI market will have two highly capable models fighting for the same enterprise customers at virtually the same price point. GPT-5.6 Sol, the flagship, scored 96.7 percent on Terminal-Bench 2.1 for command-line and agentic workflows, a new state-of-the-art result that also happens to be the cybersecurity benchmark threshold that triggered the government review process. Sol remains in restricted preview for approximately 20 approved government and enterprise partners. Luna, the third model, is the fastest and cheapest option in the family. The competitive implication is straightforward. September 1 is when Claude Sonnet 5 introductory pricing expires and steps up to three dollars per million tokens. If Terra launches before September at a lower price point, enterprise customers evaluating annual contracts will face a genuine choice where the outcome is not obvious. That is a situation OpenAI has not been in for the better part of a year. The next two weeks will determine which lab enters the second half of 2026 with pricing momentum. Keywords: GPT-5.6 Sol Terra Luna, OpenAI price war, Claude Sonnet 5 vs GPT-5.6, AI model pricing 2026