I am a U.S. native speaker and I use it. Is it old-fashioned or "literary?" My personal check on usage is to do a search on Google News. Newspapers are usually written in good modern English that is not formal or literary, but is also free from slang and colloquialisms. The first hit is a headline in Bloomberg News, "Why Xi Jinping Needn't Worry About China's Yield-Curve Inversion." Bloomberg News is a financial news source used by professionals. Another is from "People" magazine. This is written in informal, conversational English and concerns the lives of celebrities, so it's definitely not old-fashioned. "So if newlyweds Gucci Mane and Keyshia Ka’oir want advice, they needn’t look any further than the Real Housewives of Atlanta star." A third is from a concert review from the Oakland Press, a mid-sized city newspaper: "And if anyone doubted his sincerity, the singer and guitarist checked at least a dozen times during the dynamic 21-song, just over two-hour show to make sure a good time was indeed being had by all. Homme needn’t have worried." The American Heritage Dictionary includes it, defines it simply as "contraction of 'need not,'" says nothing about it being British, and doesn't give any usage notes. So I would say that the word "needn't" is currently used by U.S. native speakers and is a part of modern U.S. English.

Hola Esther! Soy Steven y vivo en Barcelona. Cómo estás? Present tense: she doesn't need to get up early today" or "she doesn't need get up early today". Those sentences have the same meaning: It's not neccesary to get up early today. **** The first sentence is correct but the second sentence is not grammatically correct. You have to include the "to" as in the first example to be correct. The meaning you have is correct. Past tenses: "she doesn't need to get up early this morning" (we don't know if she did it or not). "She needn't have got up early this morning" (but she have). In the first sentence perhaps she didn't get up early, but in the second one it's sure that she did. -- She doesn't need to get up early this morning. (this hasn't happened yet so it is not really past tense, it is actually present, if this was after the event it would say :She didn't need to get up early this morning. She needn't have GOTTEN up early this morning. (You are correct that she did get up early but it wasn't necessary. When we use have with another verb as in this example, we need to use the past participle form of the second verb, in this case: gotten.) We never use needn't in the US, instead we say "didn't need to......."As far as I know it is still common to use in the UK. I hope this helps and Que tengas una buena noche!

In the UK, we don't use it a lot any more and you don't need to use it. I would not teach it to a student before C1 level and I would never expect a student to use it in their own speech or writing. The most common usage is the perfect/past form e.g. I bought so much food for the party but I needn't have bothered - only 3 people came. (= I did not need to bother)

"Needn't" might be slightly old-fashioned and not as common as the alternatives, but it is alive and well in most English dialects including American English. However, you needn't use it. I would not call it formal at all - it is really extremely polite and kind-sounding.

Has recibido buenas respuestas. Anadire que, si, he escuchado "need not" en ingles eeuu; no es comun, claro esta, pero, se oye, como: "You need not go to all that trouble." = You don't have to do that to help me.