diff --git a/src/EncoderProvider.php b/src/EncoderProvider.php
index 331dfdb..6b29688 100644
--- a/src/EncoderProvider.php
+++ b/src/EncoderProvider.php
@@ -47,6 +47,7 @@ final class EncoderProvider implements ResetInterface
         ],
     ];
     private const MODEL_PREFIX_TO_ENCODING = [
+        'o1-' => 'o200k_base',
         'gpt-4o-' => 'o200k_base',
         'gpt-4-' => 'cl100k_base',
         'gpt-3.5-turbo-' => 'cl100k_base',