swapped K3 into the middle seat of my stack this morning. same checker, same specs, same tasks

first honest impressions after 19 runs:
> frontend is the massacre zone: a macOS-style UI from a single prompt in 15 minutes, devs flat out calling it better than Fable 5 and Sol for frontend work
> visual scene-building vs Opus 4.8 "isn't even close": full textures, lighting, working detail against a gray box
> the eval crowd's one-liner: opus level, strictly better than 4.8 across the board, at Sonnet pricing > where Fable still holds: deep reasoning and long-horizon agent runs. nobody has dethroned the planner seat yet
vendor benchmarks tell you what a model can do. your own checker tells you what it will do for you
full verdict after a week of night shifts