(FWIW I have definitely noticed a cognitive decline with Claude / Opus 4.6 over the past month and a half or so, and unless I'm secretly working for them in my sleep, I'm definitely not an Anthropic employee.)
You definitely shouldn't trust me, as we're way beyond the point where you can trust ANYTHING on the internet that has a timestamp later than 2021 or so (and even then, of course people were already lying).
Personally I use Claude models through Bedrock because I work for Amazon, and I haven't noticed any decline. Instead it's always been pretty shit, and what people describe now as the model getting lost of infinite loops of talking to itself happened since the very start for me.