The phrase "lets know" can be used to indicate a desire to acquire information or receive an update on a particular subject. Some antonyms for this phrase include "keep in the dark," "withhold information," and "conceal." These terms suggest a refusal to share information or deliberately keeping someone in ignorance. Another antonym could be "ignore," indicating a lack of interest or concern for the information being requested. Additionally, "silence" or "mum's the word" could also serve as antonyms, implying a deliberate decision not to reveal or discuss certain information with others. Overall, these antonyms suggest a lack of communication, transparency, and openness.