The English idiom turn into a pumpkin comes from the fairy tale story of Cinderella, in which the protagonist’s ragged clothes are magically transformed into an elegant gown and a pumpkin is transformed into a carriage, allowing her to attend a royal ball. She is warned that the magic wears off at midnight, upon which her clothes and carriage return to their original forms.

In some fields, the idiom turn into a pumpkin means to regress to a previous level of performance after a period of marked (but perhaps inexplicable) improvement. “The widget install success rate has gone up from 90% to 95%, which is great, but we don’t have a good understanding of why this is happening, since we haven’t made any significant changes to widget installation. It won’t be surprising if this improvement turns into a pumpkin.” (In other words, if this improvement vanishes just as mysteriously as it appeared.)

At Microsoft, the phrase turn into a pumpkin also applies to expected reductions in performance: During the period between the United States Thanksgiving holiday (the end of November) and continuing through Christmas (December 25) to the end of the year, a large percentage of people take vacation, leaving teams running on what feels like a skeleton crew. In anticipation of this reduction, many engineering services scale back their capacity. For example, a minor branch might not get any builds at all, and the major branches might build only once a day instead of twice.

Now you know what somebody means when they say something like, “We should wrap this up before people turn into pumpkins at the end of the year.”

Bonus chatter: Other citations I’ve found

The installation will turn into a pumpkin at the end of the trial period.

In this case, this is saying that the installation will cease to function at the end of the trial period. It will lose its magical powers and become about as useful as a pumpkin.

We should ask Chris before he turns into a pumpkin.

This could mean “We should ask Chris before he goes on vacation.” I’ve also seen it used in online meetings when one participant is joining from a far-away time zone at what for them is an inconvenient time. In this case, it means “We should ask Chris before he falls asleep from exhaustion.”