I’ve had Opus struggle on trivial things that Sonnet 3.5 handled with ease.

It’s not so much that the implementations are bad because the code is bad (the code is bad). It’s that it gets extremely confused and starts to frantically make worse and worse decisions and questioning itself. Editing multiple files, changing its mind and only fixing one or two. Reseting and overriding multiple batches of commits without so much as a second thought and losing days of work (yes, I’ve learned my lesson).

It, the model, can’t even reason with the decisions it’s making from turn to turn. And the more opaque agentic help it’s getting the more I suspect that tasks are being routed to much lesser models (not the ones we’ve chosen via /model or those in our agent definitions) however Anthropic chooses.

In these moments I mind as well be using Haiku.

Possible, though you eventually run into types of issues that you recall the model just not having before. Like accessing a database or not following the SOP you have it read each time it performs X routine task. There are also patterns that are much less ambiguous like getting caught in loops or failing to execute a script it wrote after ten attempts.