bevorstehend
upcoming
Describes an event, task, or situation that will take place in the near future; imminent.
Wegen der bevorstehenden Prüfung ist sie sehr nervös.
Because of the upcoming exam, she is very nervous.

upcoming
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upcoming
Describes an event, task, or situation that will take place in the near future; imminent.
Wegen der bevorstehenden Prüfung ist sie sehr nervös.
Because of the upcoming exam, she is very nervous.

'Bevorstehend' (upcoming) is the present participle of the verb 'bevorstehen' (to be imminent). This verb literally means 'to stand before something.' An upcoming event is therefore one that is directly ahead of you in time.
Das bevorstehende Wochenende wird sonnig.
The upcoming weekend will be sunny.
This adjective is almost always used attributively, meaning directly before a noun. The predicative form ('Das Ereignis ist bevorstehend.' — The event is upcoming.) is grammatically correct but uncommon. You would more likely say: 'Das Ereignis steht bevor.' (The event is imminent/upcoming.)
Alle Mitarbeiter wurden über die bevorstehenden Änderungen informiert.
All employees were informed about the upcoming changes.
'Bevorstehend' (upcoming) is typically combined with nouns that describe events, appointments, or periods of time. Common combinations include 'bevorstehende Reise' (upcoming trip), 'bevorstehende Geburt' (upcoming birth), or 'bevorstehendes Treffen' (upcoming meeting).
Wegen seines bevorstehenden Umzugs hat er viel zu organisieren.
Because of his upcoming move, he has a lot to organize.
next / nearest
'nächst' and 'bevorstehend' can both point to something in the near future. 'nächst' is very common and neutral: 'der nächste Termin' (the next appointment), 'nächste Woche' (next week), 'das nächste Treffen' (the next meeting). 'bevorstehend' is more likely to describe an event, task, or situation that will happen soon and is often important or prepared for. It sounds somewhat more formal than 'nächst'. So in everyday language, you usually say 'der nächste Termin', but in reports or more serious situations you are more likely to see 'die bevorstehende Prüfung' (the upcoming exam) or 'die bevorstehenden Änderungen' (the upcoming changes).

Wegen der bevorstehenden Prüfung lernt Ali jeden Abend.
Because of the upcoming exam, Ali studies every evening.
Marie kauft schon Getränke für das nächste Familienfest.
Marie is already buying drinks for the next family celebration.