The main venues, by volume:
Bitcoin Knots Discord — explicitly described as "the live discussion" venue. This is where the day-to-day coordination, mining questions, and community debate happen.
X (formerly Twitter) — where the broader public controversy and back-and-forth (e.g., David Schwartz vs. BIP-110 advocates) is playing out.
GitHub PR #359 on the Bitcoin Knots repo — where the technical/code review discussion lives (replay protection, retarget rules, difficulty constants, etc.).
Nostr — used for announcements (like the activation string), but not a primary discussion hub for this fork.
