diff --git a/ProcessMaker/Models/FormalExpression.php b/ProcessMaker/Models/FormalExpression.php
index 838944d60e..12cc91aad0 100644
--- a/ProcessMaker/Models/FormalExpression.php
+++ b/ProcessMaker/Models/FormalExpression.php
@@ -9,6 +9,7 @@
 use ProcessMaker\Exception\SyntaxErrorException;
 use ProcessMaker\Nayra\Bpmn\BaseTrait;
 use ProcessMaker\Nayra\Contracts\Bpmn\FormalExpressionInterface;
+use ProcessMaker\Support\PmFunctionRegistry;
 use Symfony\Component\ExpressionLanguage\ExpressionLanguage;
 use Symfony\Component\ExpressionLanguage\SyntaxError;
 use Throwable;
@@ -31,8 +32,6 @@ class FormalExpression implements FormalExpressionInterface
         'FEEL' => ['feelExpression', 'feelEncode'],
     ];
 
-    private static $pmFunctions = [];
-
     /**
      * FEEL expression object to be used to evaluate
      * @var ExpressionLanguage
@@ -55,7 +54,29 @@ protected function initFormalExpression()
      */
     public function registerPMFunction($name, callable $callable)
     {
-        static::$pmFunctions[$name] = $callable;
+        PmFunctionRegistry::register($name, $callable);
+
+        // Also register into the current ExpressionLanguage instance if initialized
+        if ($this->feelExpression instanceof ExpressionLanguage) {
+            $this->feelExpression->register(
+                $name,
+                function () {
+                },
+                $callable
+            );
+        }
+    }
+
+    /**
+     * Reset runtime-registered PM functions.
+     *
+     * Called by Octane's RequestTerminated listener to clear request-scoped
+     * functions and prevent accumulation across requests. Boot-time functions
+     * are preserved in the registry and re-registered on the next request.
+     */
+    public static function resetPmFunctions(): void
+    {
+        PmFunctionRegistry::reset();
     }
 
     /**
@@ -274,7 +295,7 @@ function ($arguments, $array, $key, $default) {
         );
 
         // Register global PM functions from packages
-        foreach (static::$pmFunctions as $name => $callable) {
+        foreach (PmFunctionRegistry::all() as $name => $callable) {
             $this->feelExpression->register(
                 $name,
                 function () {
diff --git a/ProcessMaker/Octane/ResetRequestState.php b/ProcessMaker/Octane/ResetRequestState.php
index 45071e97ad..0defa5b56a 100644
--- a/ProcessMaker/Octane/ResetRequestState.php
+++ b/ProcessMaker/Octane/ResetRequestState.php
@@ -5,6 +5,7 @@
 namespace ProcessMaker\Octane;
 
 use ProcessMaker\Listeners\HandleRedirectListener;
+use ProcessMaker\Models\FormalExpression;
 use ProcessMaker\Providers\ProcessMakerServiceProvider;
 
 final class ResetRequestState
@@ -13,5 +14,6 @@ public function handle(): void
     {
         ProcessMakerServiceProvider::beginRequestTiming();
         HandleRedirectListener::reset();
+        FormalExpression::resetPmFunctions();
     }
 }
diff --git a/ProcessMaker/Support/PmFunctionRegistry.php b/ProcessMaker/Support/PmFunctionRegistry.php
new file mode 100644
index 0000000000..0b8352ad9a
--- /dev/null
+++ b/ProcessMaker/Support/PmFunctionRegistry.php
@@ -0,0 +1,50 @@
+<?php
+
+namespace ProcessMaker\Support;
+
+/**
+ * Bounded registry for PM functions.
+ *
+ * Stores callables by name and supports resetting to boot-time state.
+ * Designed as a standalone utility to avoid static state in FormalExpression.
+ */
+class PmFunctionRegistry
+{
+    private static array $functions = [];
+
+    private static array $bootFunctions = [];
+
+    private static bool $bootTracking = true;
+
+    public static function register(string $name, callable $callable): void
+    {
+        self::$functions[$name] = $callable;
+
+        if (self::$bootTracking && !isset(self::$bootFunctions[$name])) {
+            self::$bootFunctions[$name] = $callable;
+        }
+    }
+
+    public static function all(): array
+    {
+        return self::$functions;
+    }
+
+    public static function reset(): void
+    {
+        self::$bootTracking = false;
+        self::$functions = self::$bootFunctions;
+    }
+
+    /**
+     * Clear all registered functions.
+     *
+     * Intended for test isolation or complete teardown.
+     */
+    public static function clear(): void
+    {
+        self::$functions = [];
+        self::$bootFunctions = [];
+        self::$bootTracking = true;
+    }
+}
diff --git a/tests/unit/ProcessMaker/Models/FormalExpressionOctaneTest.php b/tests/unit/ProcessMaker/Models/FormalExpressionOctaneTest.php
new file mode 100644
index 0000000000..66ed5fda6b
--- /dev/null
+++ b/tests/unit/ProcessMaker/Models/FormalExpressionOctaneTest.php
@@ -0,0 +1,180 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\ProcessMaker\Models;
+
+use ProcessMaker\Models\FormalExpression;
+use ProcessMaker\Octane\ResetRequestState;
+use ProcessMaker\Support\PmFunctionRegistry;
+use Tests\TestCase;
+
+/**
+ * Test that pmFunctions registry does not leak state between Octane requests.
+ */
+class FormalExpressionOctaneTest extends TestCase
+{
+    private function registry(): PmFunctionRegistry
+    {
+        // Fresh registry instance for test isolation
+        return app()->make(PmFunctionRegistry::class);
+    }
+
+    public function test_pm_functions_do_not_accumulate_across_requests(): void
+    {
+        PmFunctionRegistry::clear();
+        FormalExpression::resetPmFunctions();
+
+        // Request 1: register a custom PM function (runtime registration)
+        $formalExp1 = new FormalExpression();
+        $formalExp1->setLanguage('FEEL');
+        $formalExp1->setBody('customFn("test") == "test"');
+
+        $reflection = new \ReflectionClass($formalExp1);
+        $method = $reflection->getMethod('registerPMFunction');
+        $method->setAccessible(true);
+        $method->invoke($formalExp1, 'customFn', function ($arguments, $arg) {
+            return (string) $arg;
+        });
+
+        $this->assertCount(1, $this->registry()->all());
+
+        // Simulate Octane RequestTerminated reset
+        $resetState = new ResetRequestState();
+        $resetState->handle();
+
+        // After reset, runtime-registered functions should be cleared
+        $this->assertCount(0, $this->registry()->all());
+
+        // Request 2: register another custom function after reset
+        $formalExp2 = new FormalExpression();
+        $formalExp2->setLanguage('FEEL');
+
+        $reflection2 = new \ReflectionClass($formalExp2);
+        $method2 = $reflection2->getMethod('registerPMFunction');
+        $method2->setAccessible(true);
+        $method2->invoke($formalExp2, 'anotherFn', function ($arguments, $arg) {
+            return strtoupper((string) $arg);
+        });
+
+        // Only the new function should exist after reset
+        $this->assertCount(1, $this->registry()->all());
+        $this->assertArrayHasKey('anotherFn', $this->registry()->all());
+    }
+
+    public function test_built_in_functions_are_always_available(): void
+    {
+        $formalExp = new FormalExpression();
+        $formalExp->setLanguage('FEEL');
+        $formalExp->setBody('date("Y") > 1900');
+        $this->assertTrue($formalExp([]));
+    }
+
+    public function test_custom_pm_function_is_evaluable(): void
+    {
+        $formalExp = new FormalExpression();
+        $formalExp->setLanguage('FEEL');
+        $formalExp->setBody('greet("World") == "Hello, World!"');
+
+        $reflection = new \ReflectionClass($formalExp);
+        $method = $reflection->getMethod('registerPMFunction');
+        $method->setAccessible(true);
+        $method->invoke($formalExp, 'greet', function ($arguments, $name) {
+            return 'Hello, ' . $name . '!';
+        });
+
+        $this->assertTrue($formalExp([]));
+    }
+
+    public function test_registering_same_function_twice_overwrites(): void
+    {
+        $formalExp = new FormalExpression();
+        $formalExp->setLanguage('FEEL');
+
+        $reflection = new \ReflectionClass($formalExp);
+        $method = $reflection->getMethod('registerPMFunction');
+        $method->setAccessible(true);
+
+        $method->invoke($formalExp, 'double', function ($arguments, $x) {
+            return $x * 2;
+        });
+
+        $method->invoke($formalExp, 'double', function ($arguments, $x) {
+            return $x * 3;
+        });
+
+        $formalExp->setBody('double(2) == 6');
+        $this->assertTrue($formalExp([]));
+    }
+
+    public function test_pm_functions_static_array_does_not_grow_with_instances(): void
+    {
+        PmFunctionRegistry::clear();
+        FormalExpression::resetPmFunctions();
+
+        $initialCount = count($this->registry()->all());
+
+        for ($i = 0; $i < 10; $i++) {
+            $exp = new FormalExpression();
+            $exp->setLanguage('FEEL');
+        }
+
+        $this->assertCount($initialCount, $this->registry()->all());
+    }
+
+    public function test_reset_pm_functions_restores_boot_time_state(): void
+    {
+        PmFunctionRegistry::clear();
+
+        // Register a boot-time function
+        $formalExp = new FormalExpression();
+        $reflection = new \ReflectionClass($formalExp);
+        $method = $reflection->getMethod('registerPMFunction');
+        $method->setAccessible(true);
+        $method->invoke($formalExp, 'bootFn', function () {
+        });
+
+        // Mark current state as boot baseline
+        FormalExpression::resetPmFunctions();
+
+        // Register a runtime function after the boot baseline
+        $method->invoke($formalExp, 'runtimeFn', function () {
+        });
+
+        $this->assertCount(2, $this->registry()->all());
+
+        // Reset should clear runtime functions, keeping only boot-time
+        FormalExpression::resetPmFunctions();
+
+        $this->assertCount(1, $this->registry()->all());
+        $this->assertArrayHasKey('bootFn', $this->registry()->all());
+        $this->assertArrayNotHasKey('runtimeFn', $this->registry()->all());
+    }
+
+    public function test_boot_time_functions_survive_reset(): void
+    {
+        PmFunctionRegistry::clear();
+
+        // Register a boot-time function
+        $formalExp = new FormalExpression();
+        $reflection = new \ReflectionClass($formalExp);
+        $method = $reflection->getMethod('registerPMFunction');
+        $method->setAccessible(true);
+        $bootFn = function () {
+        };
+        $method->invoke($formalExp, 'bootFn', $bootFn);
+
+        // Mark current state as boot baseline
+        FormalExpression::resetPmFunctions();
+
+        // Register a runtime function after the boot baseline
+        $method->invoke($formalExp, 'runtimeFn', function () {
+        });
+
+        // Reset should preserve bootFn
+        FormalExpression::resetPmFunctions();
+
+        $this->assertCount(1, $this->registry()->all());
+        $this->assertSame($bootFn, $this->registry()->all()['bootFn']);
+    }
+}