Writing a formal sunset announcement comes down to two decisions: which voice to use, and which preposition matches your timeframe.
Most formal sunset announcements use the passive voice -- "X will be sunset on [date]" -- paired with a correct timeframe preposition ("by," "on," "in," or "over," never "until"). Get both right and the announcement reads as calm, deliberate, and professional; get either wrong and it reads as either evasive or simply foreign.
Why passive voice dominates formal announcements
Passive voice dominates real formal announcements because the focus is on the thing ending, not on who is ending it.
"The v1 API will be sunset on March 1, 2027."
"This legacy benefit will be fully sunset by the end of Q4."
Progressive active voice is also natural, specifically when describing a transition already in progress rather than a future event.
"We are sunsetting the on-premise version over the next six months."
Neither voice is more "correct" than the other -- the choice depends on whether you're announcing a future decision (passive fits well) or narrating a transition that's already underway (progressive active fits well).
Matching the preposition to the kind of date
Whichever voice you choose, the timeframe preposition has to match the kind of date. "By" signals a deadline -- the ending happens no later than that point. "On" signals a single date. "In" signals a period. "Over" signals a span, a duration the ending happens across rather than at.
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Start learning for free →Getting this wrong doesn't just sound slightly off -- it can genuinely misstate the timeline, which is exactly the kind of ambiguity a formal announcement is supposed to eliminate.
The one preposition that's always wrong
"Sunset until [date]" is never correct English, regardless of voice. A common slip is reaching for "until" instead of a real timeframe preposition -- "sunset until Q3" is not natural English; use "by Q3," "in Q3," or "over Q3" instead, depending on whether you mean a deadline, a single point, or a span.
Before sending any formal sunset announcement, check both pieces separately: does the voice match whether this is a future decision or an ongoing transition, and does the preposition actually match the kind of date you're naming?
Why both pieces matter more in a formal document
A quick internal Slack message can survive a slightly off preposition or an inconsistent voice without much cost -- the reader fills in the gap from context. A formal announcement, the kind that goes into a leadership deck, a client email, or an official policy update, doesn't get that same benefit of the doubt. Readers of formal documents tend to parse the exact wording more carefully, partly because the document itself is signaling that the decision is significant enough to write down formally.
That's why it's worth treating voice and preposition as two separate checks rather than one general "does this sound right" pass. A sentence can get the voice exactly right and still misstate the timeline with the wrong preposition, or vice versa -- get the timeframe right but choose a voice that makes the announcement sound more tentative, or more sudden, than the decision actually is.
Practice scenarios
Practice using sunset in situations like:
- choosing between passive and progressive active voice for a sunset announcement
- matching the right timeframe preposition to a deadline, a date, or a span
- catching an incorrect "sunset until" before an announcement goes out
Useful practice phrases:
- "The v1 API will be sunset on March 1, 2027."
- "This legacy benefit will be fully sunset by the end of Q4."
- "We are sunsetting the on-premise version over the next six months."
A formal sunset announcement is really just two small decisions, made correctly, in the same sentence.
Get the voice and the preposition right, and the rest of the announcement reads as calm and deliberate on its own.
Lyra Practice helps advanced non-native English professionals learn the nuance of high-value workplace expressions and practice using them in realistic scenarios, so their English sounds natural, precise, and senior at work. Try Lyra Practice.