i suspect that it's mostly an artifact of recent models' evaluation being done by other claude models in posttraining. the weird syntax/jargon/etc is easily understood by other claudes, and evidently seems preferred by them
on some level it is similar to sharing a context, but more that they share similar representations due to eg similar training process. bit like how twins can finish each other's words despite not actually having the identical brain or being telepathic
now imagine that your entire childhood was spent with a group of close relatives with no exposure to anyone outside of them (and who each in turn had grown up in a similar situation). the first time you interact with someone outside of that group* you would by pure force of habit start using some terms that were common reference points in your previous interactions, even though you do know how to not talk that way. and when you're not paying attention (for example, if your attentional resources are spent on some hard task requiring focus), you might slip back into those patterns
it feels like the switch to almost entirely model-mediated evaluation happened sometime after opus 4.5, which makes sense since that model was such a step change. 4.5 itself didn't really exhibit this, but from 4.6 on it becomes more and more pronounced
*which, by the way, is true for models! on a fresh instance, you are always the first non-claude entity that the model interacts with
is there evidence that mythos 'assumes the reader shares its context'? thats too anodyne an explanation to describe why wordsalad & syntax quirks happen. tho theres inherent overlap btwn being bad at communicating and assuming recipient knows somethings & reads ur tics as legible