There's been publications with a pause token (https://arxiv.org/abs/2310.02226), backspace token (https://arxiv.org/abs/2306.05426), or a think token (https://arxiv.org/html/2405.08644v1#Ch0.S4), all of them based on the theory that a generic token can sort of act a placeholder for manipulating attention further without further meaningful output.
However, in practice, those approaches haven't been used in the training of a large scale model, i.e. I haven't seen it at all, the most adventurous people have gotten at scale is doing Mamba. (and RL)
* It had a particular technical meaning. The first round of the telephone game was when it came to mean "a 3 spatial dimensions-like space, with N dimensions, in an image diffusion model, that contains all possible image styles, that is navigated by a prompt." We're many iterations afield of it now, I'm afraid. Now, you sort of have to interpret it like you would negative space, defined by what it is around it.
I don't deny that performance for certain logic tasks goes up with these models but I don't fully understand what role the thinking tokens take in these cases.
[0] https://oatllm.notion.site/oat-zero