Fable did build me an entire platform, and Opus 5.5 is a close runner up.

Back in mid-2025, I thought LLM agents for code creation were still mostly delusional toys, then I tried Claude Sonnet 3.5 and I "converted." Using Sonnet 3.5 wasn't what I would call "clearly more productive" - yet. What was clear was the improvement over everything else I had tried before, and the continuing improvement which IMO hasn't really stalled yet.

Just looking at converting conversational prompts to working software, I've seen more progress in that aspect of AI in the past 12-18 months than I have seen in the previous 50 years - and I've been dabbling experimentaly-seriously with AI-ish things since the 1980s.

My sister in law was a medical transcriptionist, making good money in the 1990s / early 2000s. Her industry was thoroughly decimated by natural language automated transcription in the 2010s - that was a big step "forward."

Alpha-Zero dominating human players not only in Go, but in basically any "perfect information" game with codifiable rules... that was another big step.

Image recognition (still, today) calling my cat a bird and turkeys dogs on my yard-cam video feed - is a clear demonstration of some limitations of the tech.

I will say, the other models (Grok 4.7, Gemini 3.8) have done a lot of catching up, they're now clearly better than Sonnet 3.5 - but still not catching Claude's frontier coding abilities.