The last 8-track cartridge was FM's Greatest Hits

[vermicious knid]

From Wikipedia:

There is a debate among collectors about what was the last commercially released 8 track by a major label, but many agree it was Fleetwood Mac's Greatest Hits in November 1988.[4]. The last 8-track tapes by major recording companies were from record and tape clubs in 1988 like RCA (BMG Music) and Columbia House (CRC).

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It is an interesting distinction to have. Personally, I have Rumours and Tusk on 8-track.