Claude Sonnet 4.6, released on February 17, 2026, is the model that made the "when do I need Opus?" question genuinely hard to answer. It scores 79.6% on SWE-bench Verified — just 1.2 points behind Opus 4.6's 80.8% — while costing one-fifth the price. Add a 1 million token context window and 300K-token batch output, and you get a model that erases...