diff --git a/src/agentex/lib/utils/completions.py b/src/agentex/lib/utils/completions.py
index f33495c1..fe62c7d1 100644
--- a/src/agentex/lib/utils/completions.py
+++ b/src/agentex/lib/utils/completions.py
@@ -6,6 +6,7 @@
 
 from agentex.lib.types.llm_messages import (
     Delta,
+    Usage,
     Choice,
     ToolCall,
     Completion,
@@ -21,6 +22,8 @@ def _concat_chunks(_a: None, b: Any):
 @_concat_chunks.register
 def _(a: Completion, b: Completion) -> Completion:
     a.choices = [_concat_chunks(*c) for c in zip(a.choices, b.choices, strict=False)]
+    a.usage = _concat_chunks(a.usage, b.usage)
+
     return a
 
 
@@ -35,6 +38,17 @@ def _(a: Choice, b: Choice) -> Choice:
     a.finish_reason = a.finish_reason or b.finish_reason
     return a
 
+@_concat_chunks.register
+def _(a: Usage | None, b: Usage | None) -> Usage | None:
+    if a is not None and b is not None:
+        return Usage(
+            prompt_tokens=a.prompt_tokens + b.prompt_tokens,
+            completion_tokens=a.completion_tokens + b.completion_tokens,
+            total_tokens=a.total_tokens + b.total_tokens,
+        )
+    else:
+        return a or b
+
 
 @_concat_chunks.register
 def _(a: Delta, b: Delta) -> Delta: