Like married couples, PACS partners are subject to joint taxation (Article 6, 1 CGI and 7 CGI), including for the income earned in the year the agreement is concluded (Article 6, 5th CGI). However, you can opt for separate taxation of the income you personally received during the year of the PACS as well as your share of the joint income (Article 6, 5th CGI).
Good to know: If you cannot justify this share, the joint income is then split into two equal parts (Article 6, 5th CGI).