Is this specifically gpt-5-thinking or whatever is the default gpt-5 on chatgpt.com?

First bit of evidence: GPT-5 nails the duct-taped ham sandwich question in a temporary chat (with supposedly no access to my chat history):

Alice has a stack of 5 ham sandwiches with no condiments. She takes her walking stick and uses duct tape to attach the bottom of her walking stick to the top surface of the top sandwich. She then carefully lifts up her walking stick and leaves the room with it, going into a new room. How many complete sandwiches are in the original room and how many in the new room?

GPT-5's answer:

4 in the original room, 0 in the new room.

She taped the stick to the top surface of the top slice of bread. With no condiments acting as glue, lifting peels off just that top slice. What’s left on the stack is 4 complete sandwiches plus one mutilated (ham + bottom bread). She carries only a slice of bread—so no complete sandwich leaves the room.