diff --git a/CacheTrait.php b/CacheTrait.php
index c2f6580..4c5449b 100644
--- a/CacheTrait.php
+++ b/CacheTrait.php
@@ -38,7 +38,7 @@ public function delete(string $key): bool
     private function doGet(CacheItemPoolInterface $pool, string $key, callable $callback, ?float $beta, ?array &$metadata = null, ?LoggerInterface $logger = null): mixed
     {
         if (0 > $beta ??= 1.0) {
-            throw new class(sprintf('Argument "$beta" provided to "%s::get()" must be a positive number, %f given.', static::class, $beta)) extends \InvalidArgumentException implements InvalidArgumentException {};
+            throw new class(\sprintf('Argument "$beta" provided to "%s::get()" must be a positive number, %f given.', static::class, $beta)) extends \InvalidArgumentException implements InvalidArgumentException {};
         }
 
         $item = $pool->getItem($key);
@@ -54,7 +54,7 @@ private function doGet(CacheItemPoolInterface $pool, string $key, callable $call
                 $item->expiresAt(null);
                 $logger?->info('Item "{key}" elected for early recomputation {delta}s before its expiration', [
                     'key' => $key,
-                    'delta' => sprintf('%.1f', $expiry - $now),
+                    'delta' => \sprintf('%.1f', $expiry - $now),
                 ]);
             }
         }
diff --git a/NamespacedPoolInterface.php b/NamespacedPoolInterface.php
new file mode 100644
index 0000000..cd67bc0
--- /dev/null
+++ b/NamespacedPoolInterface.php
@@ -0,0 +1,31 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Contracts\Cache;
+
+use Psr\Cache\InvalidArgumentException;
+
+/**
+ * Enables namespace-based invalidation by prefixing keys with backend-native namespace separators.
+ *
+ * Note that calling `withSubNamespace()` MUST NOT mutate the pool, but return a new instance instead.
+ *
+ * When tags are used, they MUST ignore sub-namespaces.
+ *
+ * @author Nicolas Grekas <p@tchwork.com>
+ */
+interface NamespacedPoolInterface
+{
+    /**
+     * @throws InvalidArgumentException If the namespace contains characters found in ItemInterface's RESERVED_CHARACTERS
+     */
+    public function withSubNamespace(string $namespace): static;
+}
diff --git a/composer.json b/composer.json
index f80d0b5..b713c29 100644
--- a/composer.json
+++ b/composer.json
@@ -25,7 +25,7 @@
     "minimum-stability": "dev",
     "extra": {
         "branch-alias": {
-            "dev-main": "3.4-dev"
+            "dev-main": "3.6-dev"
         },
         "thanks": {
             "name": "symfony/contracts",