Based on a true story, although as one of the clients in question, I can’t guarantee the validity of the conversation. Any similarity to any developer alive or dead is purely coincidental.
“Dave, we need to make a change to our API.”
“Is it a zero-day security issue?”
“Nah, but it’s pretty important.”
“Will it break existing clients?”
“Yeah, probably, we used to recommend 128-bit keys, and we need to jump to 512-bit keys.”
“Do you think we should tell our users?”
“Yeah, probably. Want to let marketing know?”
“Shall we tell them it’s important?”
“Nah, they’ll figure it out.”
2 weeks pass
“Hey, support have started getting a lot of calls about clients who cannot connect to our API, any idea why?”
“Did we make a change and not tell our users?”
“Do you think we should tell them?”
“Do we have to?”
Remember, even if you do give a positive notice period, your clients will need lead time to update their code.