I found sonnet 4.5 struggled with a two pointer interval merge (two sorted lists of things with start stop timestamps), but opus 4.5 managed. Then it took opus 4.6 to make it a three way or k way merge. So it reminded me of the classic Simple made Easy talk by Rich Hickey where he talks about braids. Sonnet couldn’t track two twisted braids and opus 4.6 managed a weave.

But the last few weeks Opus 4.6 seems to have got dumb again. Now it is making way more mistakes and forgetting useful things and recent context it used to manage.

I am guessing this is just Anthropic quietly dialling down the real effort as they either downsize or free up compute for someone or something else.