I've got this message from my friend: "I'll be pretty busy basically up until the 8th November." In this case, which is correct, he will be pretty busy including 8th or he will not be pretty busy from 8th anymore?
Your friend's remark is poorly worded, as clearly, you are left confused as to his availability.
If he had said, "...busy up through the 8th of November," that would indicate that he's unavailable until November 9th. Relative to the way your friend worded his remark, it indicates he won't be available until the 9th;
As used by your friend, "until" is a preposition; it refers to a fixed state of being, in time. For example, "I won't pay you, until November 9th."
Again, for clarity, he should have stated, "...busy through Nov. 8th," or, "I should be available on Nov. 9th."
"Until" is also a subordinate conjunction; this happens when "until" is followed by both a subject and a verb, forming a subjective clause.
I hope this helps!😁