I don't know whether there was an opus that ran into trouble or if they just looked at the model they had and decided that they could charge more than originally intended. sonet 4.6 presumably is either a version of sonet 4.5 with optimizations for cost instead of perf (or a haiku that also got upscaled). Anthropic is preparing for IPO this year, so it's not exactly a stretch to suggest that they might be trying to decrease their losses and increase inference margin.