Opus 4.8: What Actually Changed Under the Hood

Logosofia no Dia a Dia · May 31, 2026 · 29m

Anthropic quietly released Opus 4.8 on May 27, 2026 — a substantial checkpoint update that reworks the training data mix, post-training pipeline, and inference strategy without changing the underlying architecture. We break down the 40% more code training data from GitHub Copilot traces, the new speculative decoding with dynamic tree depth that cuts code generation time by more than half, and the improved refusal calibration that dropped over-refusals from 8.2% to 3.1%. Plus: where benchmark gains actually translate to real-world performance (and where they don't), the reception split between…