I was advised to use a copper-based anti-seize compound with titanium parts tightened against each other. Specifically, the titanium seatpost in the titanium seat tube. Titanium is said to be able to "cold weld" itself to itself. I haven't had this problem, but I check and refresh the copper-based anti-seize every couple years.
A brief internet search fails to provide definitive confirmation that copper-based anti-seize is *required* for titanium-to-titanium fasteners, but there are several references to this as "appropriate".
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