Is the word prontos the same in Brazilian and European Portuguese?

Yes

The word "prontos" is identical in meaning, grammar, and spelling in both Brazilian and Continental Portuguese. The only differences lie in pronunciation:

• The "s" sound: In most regions of Brazil, the final "s" is pronounced as a dental [s] (like the "s" in "sun"). In Continental Portuguese, the "s" is typically pronounced as a postalveolar [ʃ] (like the "sh" in "shoe").
• Vowel reduction: In Brazilian Portuguese, the unstressed "o" is pronounced as a clear, closed [u]. In Continental Portuguese, unstressed vowels are often more "clipped" or reduced, making the word sound shorter and more compressed.

Brazilian Portuguese Examples

1. Os meninos já estão prontos para a escola. (The boys are already ready for school.)
2. Os lanches estão prontos! (The snacks are ready!)
3. Os relatórios estão todos prontos. (The reports are all ready.)
4. Eles ficaram prontos bem tarde. (They got ready very late.)
5. Meus amigos já estão prontos para sair. (My friends are already ready to go out.)

Continental Portuguese Examples

1. Os rapazes já estão prontos para a escola. (The boys are already ready for school.)
2. Os lanches estão prontos! (The snacks are ready!)
3. Os relatórios estão todos prontos. (The reports are all ready.)
4. Eles ficaram prontos muito tarde. (They got ready very late.)
5. Os meus amigos já estão prontos para sair. (My friends are already ready to go out.)