diff --git a/providers/openai/responses_options.go b/providers/openai/responses_options.go
index 42cdf984c..955c17c02 100644
--- a/providers/openai/responses_options.go
+++ b/providers/openai/responses_options.go
@@ -221,6 +221,7 @@ var responsesReasoningModelIDs = []string{
 	"gpt-5.4-codex",
 	"gpt-5.5",
 	"gpt-5.5-pro",
+	"gpt-5.6-sol",
 	"gpt-oss-120b",
 }
 
diff --git a/providers/openai/responses_params_test.go b/providers/openai/responses_params_test.go
index f533c0bae..68dd08017 100644
--- a/providers/openai/responses_params_test.go
+++ b/providers/openai/responses_params_test.go
@@ -236,6 +236,13 @@ func TestValidatePreviousResponseIDPrompt(t *testing.T) {
 	}
 }
 
+func TestResponsesModelAllowlist_GPT56Sol(t *testing.T) {
+	t.Parallel()
+
+	require.True(t, IsResponsesModel("gpt-5.6-sol"))
+	require.True(t, IsResponsesReasoningModel("gpt-5.6-sol"))
+}
+
 func TestResponsesProviderMetadata_Helper(t *testing.T) {
 	t.Parallel()