After spending a couple hours working with it, it feels like a significant jump from 5.3 codex – and I know they said it wasn't theoretically the biggest jump,

After spending a couple hours working with it, it feels like a significant jump from 5.3 codex – and I know they said it wasn't theoretically the biggest jump, but this feels like the improvement of Opus 4.5 over again – that minor improvement that hits a tipping point. It just gets stuff right, first try. Its edits are better, more refined, less spaghetti-like. If you last used 5.2, try 5.4 on High.