Is the Sage Advice Compendium considered a 1st-party resource?

Question

Is Jeremy Crawford's Sage Advice Compendium considered official Wizards of the Coast content, or rather is it more his own home-rules?

Answer 1

As the "Official Rulings" section at the start of the Sage Advice Compendium states:

Official rulings on how to interpret rules are made here in the Sage Advice Compendium. The public statements of the D&D team, or anyone else at Wizards of the Coast, are not official rulings; they are advice. The tweets of Jeremy Crawford (@JeremyECrawford), the game’s principal rules designer, are sometimes a preview of rulings that will appear here.

(Originally, Crawford's tweets were sometimes considered official rulings – though tweets by other designers never were. However, as of 2019, only the rulings that appear in the Sage Advice Compendium are "official rulings".)

Other pages on the Wizards of the Coast website also refer to Sage Advice as "official rules answers" or "official clarifications of D&D rules". It's definitely an official, first-party source.

Note that rulings are interpretations of the rules. Sometimes, the rulings in the SAC merely restate what's already stated unambiguously in the rules; other times, these official rulings go beyond the rules as written and provide insight into the intent behind a rule. However, rulings are not the same as the actual rules of the game. Only those rules that appear in the D&D 5e books published by Wizards of the Coast are actually considered official rules for D&D 5e.

And regardless of what's "official", any individual group can play however they want. The official rules provide a shared starting point on how to play the game, but DMs can interpret or modify or ignore rules as they see fit. Jeremy Crawford frequently encourages those who dislike or disagree with certain rules or rulings to "follow their bliss" and play how they want to play.