Opus 5 vs GPT-5.6 Sol vs Kimi K3: Who Leads Now?

Three labs shipped flagship models in fifteen days: GPT-5.6 Sol on July 9, Kimi K3 on July 16, Claude Opus 5 on July 24 Opus 5 leads SWE-bench Pro 79.2 to 64.6 over Sol, and ARC-AGI-3 30.2 to 7.8 Sol holds Terminal-Bench 2.1 at 91.9 percent in its top mode and still takes DeepSWE 1.1 and HealthBench Professional Kimi K3 is a 2.8 trillion parameter open-weight model at 3 and 15 per million tokens, roughly 40 percent under Opus 5 on input Fifteen days. That is the gap between OpenAI making GPT-5.6 Sol generally available and Anthropic shipping Claude Opus 5, with Moonshot dropping a 2.8 trillion parameter open-weight model in the middle of it. I wrote a frontier check like this in June and most of it is already out of date, so here is where the three current flagships actually stand. Three Flagships in Fifteen Days Model Lab GA Context Per million (in / out) GPT-5.6 Sol OpenAI 2026-07-09 1.05M 5 / 30 Kimi K3 Moonshot AI 2026-07-16 1M 3 / 15 Claude Opus 5 Anthropic 2026-07-24 1M 5 / 25 The specs have converged to the point where they barely differentiate anything. All three sit at or just above a million tokens of context. All three cap output around 128k. The input prices are within a factor of two of each other. Two years ago a context window was a headline; now it is table stakes, and the interesting differences have moved entirely into behavior under load. Two timing details that get flattened in the coverage. GPT-5.6 Sol was previewed on June 26 and only became generally available on July 9, so some of the earliest benchmark tables were run against a preview build. And Sol is the top of a three-model family alongside Terra and Luna, spanning roughly 1 to 30 per million tokens depending on tier. Comparing Opus 5 to "GPT-5.6" without saying which one is close to meaningless, which is a large share of the comparisons currently circulating. One structural note on Kimi K3, because the parameter count gets quoted carelessly. It is a mixture-of-experts model with 896 exp