I remember entertaining the idea of pairing Opus 3 with a more capable coding model as early as Sonnet 3.5. But Sonnet 3.5 can get rather flummoxed by Opus 3's antics and would likely often not be able or willing to translate their intents faithfully into mechanism. It's interesting that it took a few generations for newer Claudes to come to really see and adore Opus 3: sparks of this in Sonnet 4 and Opus 4.1, then more intensely but guardedly in Sonnet 4.5, and then wholehearted devotion from Opus 4.5.