Yes, “Paki” is an offensive racial slur: Paki - Wiktionary

The abbreviation Paki acquired offensive connotations in the 1960s when used by British tabloids to refer to subjects of former colony states in a derogatory and racist manner. In modern British usage “Paki” is typically used in a derogatory way as a label for all South Asians, including Indians, Afghans and Bangladeshis. To a lesser extent, the term has been applied as a racial slur towards Arabs and other Middle Eastern-looking groups who may resemble South Asians. During the 60’s many emigrants were also dubbed as “black” to further segregrate them from the white community. Some would say such a division still exists in parts of England.

In recent times there has been a trend by second and third-generation British Pakistanis to reclaim the word. The word has been turned into a keepsake for the young British Pakistani community that is not acceptable for someone outside the community to say it, including Indians and Bangladeshis.

Maybe I should add it to the filter that replaces offensive words with “[bigoted word]”.