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

Yes

The word "antigo" is identical in meaning, spelling, and grammar in both Brazilian and Continental Portuguese. The only difference lies in pronunciation. In Brazilian Portuguese, vowels are generally more open and the syllables are articulated with more clarity and a more musical rhythm. In Continental Portuguese, vowels—especially unstressed ones—tend to be more closed, reduced, or even suppressed, which can make the word sound more "clipped" or shorter to a Brazilian ear.

Brazilian Portuguese Examples:

1. Esse carro é muito antigo. (This car is very old.)
2. Eu gosto de móveis antigos. (I like antique furniture.)
3. Ele era meu antigo colega. (He was my former colleague.)
4. A Grécia Antiga era incrível. (Ancient Greece was incredible.)
5. Este é um relógio antigo. (This is an old watch.)

Continental Portuguese Examples:

1. Esse carro é muito antigo. (This car is very old.)
2. Eu gosto de móveis antigos. (I like antique furniture.)
3. Ele era o meu antigo colega. (He was my former colleague.)
4. A Grécia Antiga era incrível. (Ancient Greece was incredible.)
5. Este é um relógio antigo. (This is an old watch.)

(Note: In the Portuguese examples, the use of the definite article before possessives, such as "o meu," is a characteristic feature of natural speech in Portugal.)