diff --git a/chatcompletion.go b/chatcompletion.go
index 7d2a658b..a1bee54b 100644
--- a/chatcompletion.go
+++ b/chatcompletion.go
@@ -683,6 +683,8 @@ func (r *ChatCompletionChunkChoice) UnmarshalJSON(data []byte) error {
 type ChatCompletionChunkChoiceDelta struct {
 	// The contents of the chunk message.
 	Content string `json:"content,nullable"`
+	// The reasoning content of the chunk message.
+	ReasoningContent string `json:"reasoning_content,nullable"`
 	// Deprecated and replaced by `tool_calls`. The name and arguments of a function
 	// that should be called, as generated by the model.
 	//