diff --git a/src/Concerns/Caching.php b/src/Concerns/Caching.php
index 8d2cf0f..91d2045 100644
--- a/src/Concerns/Caching.php
+++ b/src/Concerns/Caching.php
@@ -8,25 +8,12 @@
 use TiMacDonald\JsonApi\JsonApiResource;
 use TiMacDonald\JsonApi\JsonApiResourceCollection;
 
+/**
+ * @internal
+ * @todo can we get rid of this?
+ */
 trait Caching
 {
-    /**
-     * @internal
-     */
-    private string|null $idCache = null;
-
-    /**
-     * @internal
-     */
-    private string|null $typeCache = null;
-
-    /**
-     * @internal
-     *
-     * @var Collection<string, JsonApiResource|JsonApiResourceCollection>|null
-     */
-    private Collection|null $requestedRelationshipsCache = null;
-
     /**
      * @internal
      * @infection-ignore-all
@@ -35,51 +22,14 @@ trait Caching
      */
     public function flush()
     {
-        $this->idCache = null;
-
-        $this->typeCache = null;
-
-        if ($this->requestedRelationshipsCache !== null) {
-            $this->requestedRelationshipsCache->each(fn (JsonApiResource|JsonApiResourceCollection $relation) => $relation->flush());
-        }
+        // TODO can we just let this garbage collect?
+        $this->requestedRelationshipsCache?->each(fn (JsonApiResource|JsonApiResourceCollection $relation) => $relation->flush());
 
         $this->requestedRelationshipsCache = null;
-    }
 
-    /**
-     * @internal
-     * @infection-ignore-all
-     *
-     * @param  (callable(): string)  $callback
-     * @return string
-     */
-    private function rememberId(callable $callback)
-    {
-        return $this->idCache ??= $callback();
-    }
-
-    /**
-     * @internal
-     * @infection-ignore-all
-     *
-     * @param  (callable(): string)  $callback
-     * @return string
-     */
-    private function rememberType(callable $callback)
-    {
-        return $this->typeCache ??= $callback();
-    }
+        $this->idCache = null;
 
-    /**
-     * @internal
-     * @infection-ignore-all
-     *
-     * @param  (callable(): Collection<string, JsonApiResource|JsonApiResourceCollection>)  $callback
-     * @return Collection<string, JsonApiResource|JsonApiResourceCollection>
-     */
-    private function rememberRequestRelationships(callable $callback)
-    {
-        return $this->requestedRelationshipsCache ??= $callback();
+        $this->typeCache = null;
     }
 
     /**
@@ -89,6 +39,7 @@ private function rememberRequestRelationships(callable $callback)
      */
     public function requestedRelationshipsCache()
     {
+        // TODO can we remove this if we ditch caching? Only here for tests.
         return $this->requestedRelationshipsCache;
     }
 }
diff --git a/src/Concerns/Identification.php b/src/Concerns/Identification.php
index 76ba061..1637aa2 100644
--- a/src/Concerns/Identification.php
+++ b/src/Concerns/Identification.php
@@ -12,6 +12,10 @@
 
 trait Identification
 {
+    private string|null $idCache = null;
+
+    private string|null $typeCache = null;
+
     /**
      * @internal
      *
@@ -105,7 +109,7 @@ public function toUniqueResourceIdentifier(Request $request)
      */
     private function resolveId(Request $request)
     {
-        return $this->rememberId(fn (): string => $this->toId($request));
+        return $this->idCache ??= $this->toId($request);
     }
 
     /**
@@ -115,7 +119,7 @@ private function resolveId(Request $request)
      */
     private function resolveType(Request $request)
     {
-        return $this->rememberType(fn (): string => $this->toType($request));
+        return $this->typeCache ??= $this->toType($request);
     }
 
     /**
diff --git a/src/Concerns/Relationships.php b/src/Concerns/Relationships.php
index 3c1b184..6fe442d 100644
--- a/src/Concerns/Relationships.php
+++ b/src/Concerns/Relationships.php
@@ -23,6 +23,11 @@
 
 trait Relationships
 {
+    /**
+     * @var Collection<string, JsonApiResource|JsonApiResourceCollection>|null
+     */
+    private Collection|null $requestedRelationshipsCache = null;
+
     /**
      * @internal
      *
@@ -103,10 +108,10 @@ private function requestedRelationshipsAsIdentifiers(Request $request)
      */
     private function requestedRelationships(Request $request)
     {
-        return $this->rememberRequestRelationships(fn (): Collection => $this->resolveRelationships($request)
+        return $this->requestedRelationshipsCache ??= $this->resolveRelationships($request)
             ->only($this->requestedIncludes($request))
             ->map(fn (callable $value, string $prefix): null|JsonApiResource|JsonApiResourceCollection => $this->resolveInclude($value(), $prefix))
-            ->reject(fn (JsonApiResource|JsonApiResourceCollection|null $resource): bool => $resource === null));
+            ->reject(fn (JsonApiResource|JsonApiResourceCollection|null $resource): bool => $resource === null);
     }
 
     /**
diff --git a/src/JsonApiResource.php b/src/JsonApiResource.php
index 19030df..7df013e 100644
--- a/src/JsonApiResource.php
+++ b/src/JsonApiResource.php
@@ -10,6 +10,7 @@
 use Illuminate\Http\Resources\PotentiallyMissing;
 use Illuminate\Support\Collection;
 use stdClass;
+
 use function property_exists;
 
 abstract class JsonApiResource extends JsonResource
@@ -115,7 +116,7 @@ public function toArray(Request $request)
     }
 
     /**
-     * @return array{included?: Collection<int, JsonApiResource>, jsonapi: JsonApiServerImplementation}
+     * @return array{included?: array<int, JsonApiResource>, jsonapi: JsonApiServerImplementation}
      */
     public function with(Request $request)
     {
@@ -129,6 +130,8 @@ public function with(Request $request)
     }
 
     /**
+     * TODO this may be removed once all supported versions have `newCollection`.
+     *
      * @return JsonApiResourceCollection<int, mixed>
      */
     public static function collection(mixed $resource)
@@ -155,7 +158,7 @@ public static function newCollection(mixed $resource)
      */
     public function toResponse($request)
     {
-        // TODO: the flush call here is triggering repeated Includes::flush() cals, because of collection.s
-        return tap(parent::toResponse($request)->header('Content-type', 'application/vnd.api+json'), fn () => $this->flush());
+        // TODO: should this header be configurable? Should it be a middleware? Should we not set it if one exists?
+        return tap(parent::toResponse($request)->header('Content-type', 'application/vnd.api+json'), $this->flush(...));
     }
 }
diff --git a/src/JsonApiResourceCollection.php b/src/JsonApiResourceCollection.php
index eac3cdc..ac51b6e 100644
--- a/src/JsonApiResourceCollection.php
+++ b/src/JsonApiResourceCollection.php
@@ -42,7 +42,7 @@ private function resolveResourceIdentifiers(Request $request)
     }
 
     /**
-     * @return array{included?: Collection<int, JsonApiResource>, jsonapi: JsonApiServerImplementation}
+     * @return array{included?: array<int, JsonApiResource>, jsonapi: JsonApiServerImplementation}
      */
     public function with(Request $request)
     {
@@ -63,7 +63,8 @@ public function with(Request $request)
      */
     public function toResponse($request)
     {
-        return tap(parent::toResponse($request)->header('Content-type', 'application/vnd.api+json'), fn () => $this->flush());
+        // TODO: should this header be configurable? Should it be a middleware? Should we not set it if one exists?
+        return tap(parent::toResponse($request)->header('Content-type', 'application/vnd.api+json'), $this->flush(...));
     }
 
     /**
@@ -98,9 +99,9 @@ function (array $link): array {
      */
     public function withIncludePrefix(string $prefix)
     {
-        return tap($this, function (JsonApiResourceCollection $resource) use ($prefix): void {
-            $resource->collection->each(fn (JsonApiResource $resource): JsonApiResource => $resource->withIncludePrefix($prefix));
-        });
+        $this->collection->each(fn (JsonApiResource $resource): JsonApiResource => $resource->withIncludePrefix($prefix));
+
+        return $this;
     }
 
     /**
diff --git a/src/Support/Fields.php b/src/Support/Fields.php
index 08787ff..3dc3ce9 100644
--- a/src/Support/Fields.php
+++ b/src/Support/Fields.php
@@ -25,7 +25,7 @@ final class Fields
      */
     private WeakMap $cache;
 
-    private function __construct(WeakMap $cache = new WeakMap)
+    private function __construct(WeakMap $cache = new WeakMap())
     {
         $this->cache = $cache;
     }
@@ -78,12 +78,4 @@ private function rememberResourceType(Request $request, string $resourceType, ca
 
         return $this->cache[$request][$resourceType] ??= $callback();
     }
-
-    /**
-     * @return void
-     */
-    public function flush()
-    {
-        $this->cache = new WeakMap();
-    }
 }
diff --git a/src/Support/Includes.php b/src/Support/Includes.php
index f38df5a..23347af 100644
--- a/src/Support/Includes.php
+++ b/src/Support/Includes.php
@@ -9,6 +9,7 @@
 use Illuminate\Support\Str;
 use Symfony\Component\HttpKernel\Exception\HttpException;
 use WeakMap;
+
 use function explode;
 use function is_array;
 
@@ -24,7 +25,7 @@ final class Includes
      */
     private WeakMap $cache;
 
-    private function __construct(WeakMap $cache = new WeakMap)
+    private function __construct(WeakMap $cache = new WeakMap())
     {
         $this->cache = $cache;
     }
@@ -80,12 +81,4 @@ private function rememberIncludes(Request $request, string $prefix, callable $ca
 
         return $this->cache[$request][$prefix] ??= $callback();
     }
-
-    /**
-     * @return void
-     */
-    public function flush()
-    {
-        $this->cache = new WeakMap();
-    }
 }
diff --git a/tests/Feature/JsonApiTest.php b/tests/Feature/JsonApiTest.php
index 48a9a3c..bc1d61b 100644
--- a/tests/Feature/JsonApiTest.php
+++ b/tests/Feature/JsonApiTest.php
@@ -11,10 +11,10 @@
 use Tests\TestCase;
 use TiMacDonald\JsonApi\JsonApiResource;
 use TiMacDonald\JsonApi\JsonApiResourceCollection;
-use TiMacDonald\JsonApi\ServerImplementation;
 use TiMacDonald\JsonApi\Link;
 use TiMacDonald\JsonApi\RelationshipObject;
 use TiMacDonald\JsonApi\ResourceIdentifier;
+use TiMacDonald\JsonApi\ServerImplementation;
 
 class JsonApiTest extends TestCase
 {