diff --git a/lib/types/minimally-encoded-thread-permissions-types.js b/lib/types/minimally-encoded-thread-permissions-types.js
--- a/lib/types/minimally-encoded-thread-permissions-types.js
+++ b/lib/types/minimally-encoded-thread-permissions-types.js
@@ -13,6 +13,7 @@
 import type {
   MemberInfo,
   RawThreadInfo,
+  RelativeMemberInfo,
   RoleInfo,
   ThreadCurrentUserInfo,
 } from './thread-types.js';
@@ -125,6 +126,39 @@
   };
 };
 
+export type MinimallyEncodedRelativeMemberInfo = $ReadOnly<{
+  ...MinimallyEncodedMemberInfo,
+  +username: ?string,
+  +isViewer: boolean,
+}>;
+
+const minimallyEncodedRelativeMemberInfoValidator: TInterface<MinimallyEncodedRelativeMemberInfo> =
+  tShape<MinimallyEncodedRelativeMemberInfo>({
+    ...minimallyEncodedMemberInfoValidator.meta.props,
+    username: t.maybe(t.String),
+    isViewer: t.Boolean,
+  });
+
+const minimallyEncodeRelativeMemberInfo = (
+  relativeMemberInfo: RelativeMemberInfo,
+): MinimallyEncodedRelativeMemberInfo => ({
+  ...relativeMemberInfo,
+  minimallyEncoded: true,
+  permissions: permissionsToBitmaskHex(relativeMemberInfo.permissions),
+});
+
+const decodeMinimallyEncodedRelativeMemberInfo = (
+  minimallyEncodedRelativeMemberInfo: MinimallyEncodedRelativeMemberInfo,
+): RelativeMemberInfo => {
+  const { minimallyEncoded, ...rest } = minimallyEncodedRelativeMemberInfo;
+  return {
+    ...rest,
+    permissions: threadPermissionsFromBitmaskHex(
+      minimallyEncodedRelativeMemberInfo.permissions,
+    ),
+  };
+};
+
 export type MinimallyEncodedRawThreadInfo = $ReadOnly<{
   ...RawThreadInfo,
   +minimallyEncoded: true,
@@ -181,4 +215,7 @@
   minimallyEncodedRawThreadInfoValidator,
   minimallyEncodeRawThreadInfo,
   decodeMinimallyEncodedRawThreadInfo,
+  minimallyEncodedRelativeMemberInfoValidator,
+  minimallyEncodeRelativeMemberInfo,
+  decodeMinimallyEncodedRelativeMemberInfo,
 };