diff --git a/providers/openai/responses_options.go b/providers/openai/responses_options.go
index cd43e5a3c..b5714ef7f 100644
--- a/providers/openai/responses_options.go
+++ b/providers/openai/responses_options.go
@@ -235,6 +235,9 @@ var responsesReasoningModelIDs = []string{
 	"gpt-5.4-codex",
 	"gpt-5.5",
 	"gpt-5.5-pro",
+	"gpt-5.6-sol",
+	"gpt-5.6-terra",
+	"gpt-5.6-luna",
 	"gpt-oss-120b",
 }
 
diff --git a/providers/openai/responses_params_test.go b/providers/openai/responses_params_test.go
index 94ea54fd7..51a0f2e08 100644
--- a/providers/openai/responses_params_test.go
+++ b/providers/openai/responses_params_test.go
@@ -240,6 +240,15 @@ func TestValidatePreviousResponseIDPrompt(t *testing.T) {
 	}
 }
 
+func TestResponsesModelAllowlist_GPT56Family(t *testing.T) {
+	t.Parallel()
+
+	for _, modelID := range []string{"gpt-5.6-sol", "gpt-5.6-terra", "gpt-5.6-luna"} {
+		require.True(t, IsResponsesModel(modelID), modelID)
+		require.True(t, IsResponsesReasoningModel(modelID), modelID)
+	}
+}
+
 func TestResponsesProviderMetadata_Helper(t *testing.T) {
 	t.Parallel()