I’m assuming Opus 4 targets Trainium 2 Ultra, necessary for both efficient serving and RL training. The buildout of this system was happening over 2025, so it wasn’t yet available in the times of Opus 4.0-4.1, which is why they were slow and expensive, and not properly RLVR-trained. By the time of Opus 4.5, Trainium 2 Ultra racks were probably sufficiently available to start serving it, after it was RLVRed either on Trainium 2 Ultra or on TPU v6e pods.
I’m assuming Opus 4 targets Trainium 2 Ultra, necessary for both efficient serving and RL training. The buildout of this system was happening over 2025, so it wasn’t yet available in the times of Opus 4.0-4.1, which is why they were slow and expensive, and not properly RLVR-trained. By the time of Opus 4.5, Trainium 2 Ultra racks were probably sufficiently available to start serving it, after it was RLVRed either on Trainium 2 Ultra or on TPU v6e pods.