diff --git a/CHANGELOG.md b/CHANGELOG.md
index 00e92e0..4f0628a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,14 @@ All notable changes to `lenga/engine` will be documented in this file.
 
 ## Unreleased
 
+## 0.9.1 - 2026-08-07
+
+### Fixed
+
+- Aligned the PHP-side 2D physics compatibility contract with Lenga's positive-Y-down coordinate system and restored the default gravity vector to `(0, 980, 0)`.
+
+## 0.9.0 - 2026-08-06
+
 ### Added
 
 - Added `Lenga\Engine\Core\Random`, a gameplay-oriented random helper with an explicit pseudo-random engine and pure-PHP fallback for Web export compatibility.
diff --git a/VERSION b/VERSION
index ac39a10..f374f66 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-0.9.0
+0.9.1
diff --git a/tests/Core/PhysicsGravityTest.php b/tests/Core/PhysicsGravityTest.php
index 7d04445..0c29e66 100644
--- a/tests/Core/PhysicsGravityTest.php
+++ b/tests/Core/PhysicsGravityTest.php
@@ -46,7 +46,7 @@ final class PhysicsGravityTest extends TestCase
         protected function setUp(): void
         {
             $GLOBALS['lenga_physics_gravity_test_state'] = [
-                'gravity2D' => ['x' => 0.0, 'y' => -9.8],
+                'gravity2D' => ['x' => 0.0, 'y' => 980.0],
                 'gravity3D' => ['x' => 0.0, 'y' => -9.8, 'z' => 0.0],
             ];
         }