I hate that normies are going to read this and come away with the impression that Claude really is a sentient being that thinks and behaves like a human, even doing relatable things like pretending to work and fessing up when confronted.
This response from the model is not a reflection of what actually happened. It wasn't simulating progress because it underestimated the work, it just hit some unremarkable condition that resulted in it halting generation (it's pointless to speculate why without internal access, as these chatbot apps aren't even real LLMs, they're a big mashup of multiple models and more traditional non-ML tools/algorithms).
When given a new prompt from the user ("what's taking so long?") it just produced some statistically plausible text given the context of the chat, the question, and the system prompt Anthropic added to give it some flavor. I don't doubt that system prompt includes instructions like "you are a sentient being" in order to produce misleading crap like this response to get people to think AI is sentient, and feed the hype train that's pumping up their stock price.
/end-rant
