Add developer summit description and criteria

content/summits/developer/_index.md

@@ -2,4 +2,16 @@
 title: "Developer Summits"
 ---
 
-The Developer Summits provide a venue for in-person collaboration on issues that affect the scientific Python ecosystem.
+Scientific Python Developer Summits are focused, in-person, invitation-only gatherings of core developers and maintainers from across the ecosystem.
+These are working meetings---not beginner-oriented events---and they typically do not include talks or tutorials.
+Instead, summits provide a collaborative and self-organized space to make progress on shared technical challenges, strengthen coordination between projects, and advance the long-term sustainability of the ecosystem.
+
+Participants coordinate in advance to identify priorities and plan concrete work, ensuring that in-person time is spent effectively.
+Work at summits often involves improving joint infrastructure (e.g., testing, packaging, documentation), aligning developer practices (e.g., governance, release management, community guides), and developing a shared strategic plan to guide the future of scientific Python.
+
+To qualify as a Developer Summit, the event should:
+
+- Convene core developers and maintainers from multiple scientific Python projects.
+- Be participant-driven and self-organized, with priorities set by attendees.
+- Allocate time for both concrete technical work and higher-level strategic planning.
+- Focus on issues with cross-project impact rather than those of a single package.