diff --git a/message.go b/message.go
index 052dc114..4ff28a1b 100644
--- a/message.go
+++ b/message.go
@@ -3359,7 +3359,7 @@ func (r *InputJSONDelta) UnmarshalJSON(data []byte) error {
 // The properties Schema, Type are required.
 type JSONOutputFormatParam struct {
 	// The JSON schema of the format
-	Schema map[string]any `json:"schema,omitzero,required"`
+	Schema json.RawMessage `json:"schema,omitzero,required"`
 	// This field can be elided, and will marshal its zero value as "json_schema".
 	Type constant.JSONSchema `json:"type,required"`
 	paramObj
@@ -6367,7 +6367,6 @@ func (u ThinkingConfigParamUnion) GetType() *string {
 	return nil
 }
 
-
 type ThinkingDelta struct {
 	Thinking string                 `json:"thinking,required"`
 	Type     constant.ThinkingDelta `json:"type,required"`
diff --git a/message_test.go b/message_test.go
index 9062a015..f934694e 100644
--- a/message_test.go
+++ b/message_test.go
@@ -62,9 +62,7 @@ func TestMessageNewWithOptionalParams(t *testing.T) {
 		OutputConfig: anthropic.OutputConfigParam{
 			Effort: anthropic.OutputConfigEffortLow,
 			Format: anthropic.JSONOutputFormatParam{
-				Schema: map[string]any{
-					"foo": "bar",
-				},
+				Schema: json.RawMessage(`{"foo": "bar"}`),
 			},
 		},
 		ServiceTier:   anthropic.MessageNewParamsServiceTierAuto,
@@ -171,9 +169,7 @@ func TestMessageCountTokensWithOptionalParams(t *testing.T) {
 		OutputConfig: anthropic.OutputConfigParam{
 			Effort: anthropic.OutputConfigEffortLow,
 			Format: anthropic.JSONOutputFormatParam{
-				Schema: map[string]any{
-					"foo": "bar",
-				},
+				Schema: json.RawMessage(`{"foo": "bar"}`),
 			},
 		},
 		System: anthropic.MessageCountTokensParamsSystemUnion{
diff --git a/messagebatch_test.go b/messagebatch_test.go
index f0d609fe..4bd4b39f 100644
--- a/messagebatch_test.go
+++ b/messagebatch_test.go
@@ -4,6 +4,7 @@ package anthropic_test
 
 import (
 	"context"
+	"encoding/json"
 	"errors"
 	"os"
 	"testing"
@@ -62,9 +63,7 @@ func TestMessageBatchNew(t *testing.T) {
 				OutputConfig: anthropic.OutputConfigParam{
 					Effort: anthropic.OutputConfigEffortLow,
 					Format: anthropic.JSONOutputFormatParam{
-						Schema: map[string]any{
-							"foo": "bar",
-						},
+						Schema: json.RawMessage(`{"foo": "bar"}`),
 					},
 				},
 				ServiceTier:   "auto",