Is Matt Mercer's homebrew setting of Exandria now considered an official setting, as of the release of the "Explorer's Guide to Wildemount"?

Question

Now that Explorer's Guide to Wildemount is out, I'm curious to know how much of Matt Mercer's homebrew content is now considered "official". Since this is a first-party WotC official D&D sourcebook, does this mean that his homebrew Exandria setting and its associated lore is now to be considered an official setting, on par with the Forgotten Realms, Eberron, Dragonlance, etc.?

What about a setting makes it official, and does Matt Mercer's setting of Exandria qualify for that?

Obviously his rulings and other house rules (basically anything he's said during his shows that deviates from RAW) are in no way official, no more so than when Jeremy Crawford tweets about how he'd rule something, so I don't so much care about that.

I'm more interested in his homebrew content, specifically his setting. (I'm also interested in how much of his homebrew magic items, spells, etc., are also considered official – I'm guessing for things like that it's simply "if it's in that book, then it's official" – but the focus of this question is on the overall setting and its associated lore.)

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Why am I asking this?

This answer to another question of mine somewhat tentatively includes a reference to material from this new book, and since I asked for official lore in that question, I'm somewhat confused about whether or not it really counts as "official lore" (not to scrutinise that answer–I think it's good to include in that answer anyway; see also my comment under that question that expresses some confusion over this issue).

Answer 1

The Amazon listing for the book¹ lists the "Wizards RPG Team" as the Author, with Matt Mercer only as a Contributor. You can click the Wizards RPG Team to see their page and all the books they sell, including the PHB, DMG, Monster Manual, and more (including all the other setting books). This would indicate to me that it is truly an official setting book.

Additionally, Exandria is listed in the D&D Campaign Settings Wikipedia page. Obviously this is a publicly-editable page, but you can see for yourself that one of the references used for the Wildemount campaign there points directly to the Wizards D&D page referencing Wildemount.

Aside from that, the setting had an "official by association" status by two ways:

• the mention of Arkhan the Cruel's brief excursion to Exandria in the Baldur's Gate: Descent into Avernus module.
• to a more distant degree, in Waterdeep: Dragon Heist, Matt Mercer is pictured in the Yawning Portal Inn. This is more of a fan nod than a canon reference, of course.

On 12 October 2021, the D&D team also announced the release of the official 5E adventure module Critical Role: Call of the Netherdeep. From the release page:

Inspired by the campaigns of the hit series Critical Role, this adventure begins in the Wastes of Xhorhas and leads to the glimmering oasis-city of Ank’Harel on the continent of Marquet.

These places (Xhorhas and Marquet, etc.) are located in Exandria.

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However, I would argue that the Tal'Dorei guide book, despite also taking place on Exandria, is not an official campaign setting guide, due to not being published under the Wizards of The Coast label. It does still take place on a now-official continent in a now-official world, Exandria, but the events and characters in the Tal'Dorei book are not official unless they also appear or are referenced in the Wildemount book (or any subsequent, official WoTC books).

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¹ Stack Exchange auto-converts all Amazon product links to affiliate links for themselves, to be clear; view the source of the answer to see the unaffiliated URL.

Answer 2

Not sure if this source is considered official enough, but in an interview by Todd Kenreck with Matt Mercer posted on D&D Beyond's YouTube channel, they talk about it and treat it as an official setting, saying things like:

"Your setting is now officially part of D&D" - 0:00

and

"This is like the first universe to join D&D since Eberron..." - 6:31

Based off these remarks and what I can find online it seems to be considered a new official setting.

Another possible confirmation of it being official is the world of Exandria, where the continent of Wildemount is set, is mentioned briefly in the adventure module Baldur's Gate: Descent into Avernus under a section on Arkhan the Cruel (p. 113):

[...] his ongoing battle of wills to master the Hand of Vecna, which came into his possession during a brief excursion to the world of Exandria.

This sadly does not resolve the question about how much of Critical Role's campaign inside the world of Exandria is official, but it does seem to be that at the very least Exandria is official.