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

Yes

The word "tantos" is identical in meaning, grammar, and spelling in both Brazilian and Continental Portuguese. It is the masculine plural form of "tanto," used as an adjective or pronoun to indicate a large quantity or equality in quantity ("so many" or "as many"). The only difference lies in pronunciation. In Brazilian Portuguese, the vowels are generally more open and the rhythm is more syllable-timed (musical). In Continental Portuguese, unstressed vowels are often more closed or even reduced/swallowed, creating a more stress-timed rhythm.

Brazilian Portuguese Examples

1. Não tem tantos problemas assim. (There aren't so many problems like that.)
2. Tantos anos passaram tão rápido. (So many years passed so quickly.)
3. Ele comprou tantos doces que ficou doente. (He bought so many sweets that he got sick.)
4. Eu não sabia que tinha tantos amigos aqui. (I didn't know I had so many friends here.)
5. Tantos carros deixam a rua cheia. (So many cars leave the street full.)

Continental Portuguese Examples

1. Não há tantos problemas assim. (There aren't so many problems like that.)
2. Tantos anos passaram tão depressa. (So many years passed so quickly.)
3. Ele comprou tantos rebuçados que ficou doente. (He bought so many sweets that he got sick.)
4. Não sabia que tinha tantos amigos aqui. (I didn't know I had so many friends here.)
5. Tantos automóveis deixam a rua cheia. (So many cars leave the street full.)