Does a Developer’s Knowledge of a Major Protocol Upgrade Count as inside Information?

It can, depending on the nature and public availability of the information. If a major upgrade is expected to significantly impact the token's utility or value, and the details are known only to a small group of core developers before a public announcement, that knowledge is non-public and price-sensitive.

Trading on this information, or tipping others, could be viewed as insider dealing, especially if the token is deemed a security or derivative under relevant jurisdiction.