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

Yes

The word "os" is functionally, grammatically, and orthographically identical in both Brazilian and Continental Portuguese. It serves as the masculine plural definite article (meaning "the"). The only difference between the two variants is pronunciation. In Brazilian Portuguese, the vowel "o" is typically pronounced more clearly and the "s" is often a distinct [s] or [z] sound. In Continental Portuguese, unstressed vowels are frequently reduced or swallowed in rapid speech, making "os" sound much more clipped, often sounding like a very short "u" followed by a soft "sh" or "s" sound ([uʃ] or [us]).

Brazilian Portuguese

1. Os meninos estão brincando. (The boys are playing.)
2. Os carros são muito caros. (The cars are very expensive.)
3. Eu vi os ônibus no ponto. (I saw the buses at the stop.)
4. Os alunos estão fazendo a lição. (The students are doing the homework.)
5. Os doces são muito gostosos. (The sweets are very tasty.)

Continental Portuguese

1. Os rapazes estão a brincar. (The boys are playing.)
2. Os automóveis são muito caros. (The cars are very expensive.)
3. Eu vi os autocarros na paragem. (I saw the buses at the stop.)
4. Os alunos estão a fazer o trabalho. (The students are doing the work.)
5. Os rebuçados são muito bons. (The sweets/candies are very good.)