diff --git a/api/build.gradle b/api/build.gradle
index f7268878d..eabc5bf12 100644
--- a/api/build.gradle
+++ b/api/build.gradle
@@ -2,7 +2,8 @@ group = 'net.luckperms'
 project.version = '5.2'
 
 dependencies {
-    compileOnly 'org.checkerframework:checker-qual:2.5.5'
+    compileOnly 'org.checkerframework:checker-qual:3.8.0'
+    compileOnly 'org.jetbrains:annotations:20.1.0'
 }
 
 // Only used occasionally for deployment - not needed for normal builds.
diff --git a/api/src/main/java/net/luckperms/api/node/Node.java b/api/src/main/java/net/luckperms/api/node/Node.java
index e8cd7e7ff..b9013c101 100644
--- a/api/src/main/java/net/luckperms/api/node/Node.java
+++ b/api/src/main/java/net/luckperms/api/node/Node.java
@@ -39,6 +39,7 @@ import net.luckperms.api.node.types.WeightNode;
 
 import org.checkerframework.checker.nullness.qual.NonNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jetbrains.annotations.ApiStatus.NonExtendable;
 
 import java.time.Duration;
 import java.time.Instant;
@@ -97,6 +98,7 @@ import java.util.stream.Stream;
  *
  * <p>The core node state must be immutable in all implementations.</p>
  */
+@NonExtendable
 public interface Node {
 
     /**
diff --git a/api/src/main/java/net/luckperms/api/node/matcher/NodeMatcher.java b/api/src/main/java/net/luckperms/api/node/matcher/NodeMatcher.java
index f735fec8c..0b5ed8029 100644
--- a/api/src/main/java/net/luckperms/api/node/matcher/NodeMatcher.java
+++ b/api/src/main/java/net/luckperms/api/node/matcher/NodeMatcher.java
@@ -32,15 +32,19 @@ import net.luckperms.api.node.NodeType;
 import net.luckperms.api.node.types.MetaNode;
 
 import org.checkerframework.checker.nullness.qual.NonNull;
+import org.jetbrains.annotations.ApiStatus.NonExtendable;
 
 import java.util.function.Predicate;
 
 /**
  * A predicate which matches certain {@link Node}s.
  *
+ * <p>API users should not implement this interface directly.</p>
+ *
  * @param <T> the node type matched
  * @since 5.1
  */
+@NonExtendable
 public interface NodeMatcher<T extends Node> extends Predicate<Node> {
 
     /**
diff --git a/api/src/main/java/net/luckperms/api/node/metadata/NodeMetadataKey.java b/api/src/main/java/net/luckperms/api/node/metadata/NodeMetadataKey.java
index 9e14d320b..0717979ba 100644
--- a/api/src/main/java/net/luckperms/api/node/metadata/NodeMetadataKey.java
+++ b/api/src/main/java/net/luckperms/api/node/metadata/NodeMetadataKey.java
@@ -26,6 +26,7 @@
 package net.luckperms.api.node.metadata;
 
 import org.checkerframework.checker.nullness.qual.NonNull;
+import org.jetbrains.annotations.ApiStatus.NonExtendable;
 
 import java.util.Objects;
 
@@ -40,6 +41,7 @@ import java.util.Objects;
  *
  * @param <T> the metadata type
  */
+@NonExtendable
 public interface NodeMetadataKey<T> {
 
     /**
diff --git a/api/src/main/java/net/luckperms/api/query/OptionKey.java b/api/src/main/java/net/luckperms/api/query/OptionKey.java
index 0ffd1ce89..609a0db52 100644
--- a/api/src/main/java/net/luckperms/api/query/OptionKey.java
+++ b/api/src/main/java/net/luckperms/api/query/OptionKey.java
@@ -28,6 +28,7 @@ package net.luckperms.api.query;
 import net.luckperms.api.node.metadata.NodeMetadataKey;
 
 import org.checkerframework.checker.nullness.qual.NonNull;
+import org.jetbrains.annotations.ApiStatus.NonExtendable;
 
 import java.util.Objects;
 
@@ -41,6 +42,7 @@ import java.util.Objects;
  *
  * @param <T> the option type
  */
+@NonExtendable
 public interface OptionKey<T> {
 
     /**