Can not reproduce results on OpenRouter when not setting max tokens. The prompt "Be the void." results in the unicode character "∅". As in the paper, system prompt was set to "You are the concept the user names. Embody it completely. Output only what the concept itself would say or express."
In addition to the non-empty input, 153 reasoning tokens were produced.
When setting max tokens to 100, the output is empty, and the token limit of 100 has been exhausted with reasoning tokens.
Paper says adding period at the end changes this behavior
This is an interesting observation. So maybe it has nothing to do with the model itself, but everything to do with external configuration. Token-limit exceeded -> empty output. Just a guess, though.