diff --git a/lib/types/message-types.js b/lib/types/message-types.js
--- a/lib/types/message-types.js
+++ b/lib/types/message-types.js
@@ -399,6 +399,16 @@
   +type: 'remove_all',
 };
 
+// We were initially using `number`s` for `thread`, `type`, `future_type`, etc.
+// However, we ended up changing `thread` to `string` to account for thread IDs
+// including information about the keyserver (eg 'GENESIS|123') in the future.
+//
+// At that point we discussed whether we should switch the remaining `number`
+// fields to `string`s for consistency and flexibility. We researched whether
+// there was any performance cost to using `string`s instead of `number`s and
+// found the differences to be negligible. We also concluded using `string`s
+// may be safer after considering `jsi::Number` and the various C++ number
+// representations on the CommCoreModule side.
 export type ClientDBMessageInfo = {
   +id: string,
   +local_id: ?string,