diff --git a/modules/openapi-generator/src/main/resources/go/client.mustache b/modules/openapi-generator/src/main/resources/go/client.mustache
index 9c189b8dc212..282ad6ed56d8 100644
--- a/modules/openapi-generator/src/main/resources/go/client.mustache
+++ b/modules/openapi-generator/src/main/resources/go/client.mustache
@@ -539,6 +539,15 @@ func (c *APIClient) decode(v interface{}, b []byte, contentType string) (err err
 		*s = string(b)
 		return nil
 	}
+	if r, ok := v.(*io.Reader); ok {
+		*r = bytes.NewReader(b)
+		return nil
+	}
+	// Must stay before the JSON branch: json.Unmarshal would base64-decode into *[]byte.
+	if p, ok := v.(*[]byte); ok {
+		*p = b
+		return nil
+	}
 	if f, ok := v.(*os.File); ok {
 		f, err = os.CreateTemp("", "HttpClientFile")
 		if err != nil {
diff --git a/samples/client/echo_api/go-external-refs/client.go b/samples/client/echo_api/go-external-refs/client.go
index 01f4055c6cfe..83d93205607b 100644
--- a/samples/client/echo_api/go-external-refs/client.go
+++ b/samples/client/echo_api/go-external-refs/client.go
@@ -460,6 +460,15 @@ func (c *APIClient) decode(v interface{}, b []byte, contentType string) (err err
 		*s = string(b)
 		return nil
 	}
+	if r, ok := v.(*io.Reader); ok {
+		*r = bytes.NewReader(b)
+		return nil
+	}
+	// Must stay before the JSON branch: json.Unmarshal would base64-decode into *[]byte.
+	if p, ok := v.(*[]byte); ok {
+		*p = b
+		return nil
+	}
 	if f, ok := v.(*os.File); ok {
 		f, err = os.CreateTemp("", "HttpClientFile")
 		if err != nil {
diff --git a/samples/client/echo_api/go/client.go b/samples/client/echo_api/go/client.go
index 01f4055c6cfe..83d93205607b 100644
--- a/samples/client/echo_api/go/client.go
+++ b/samples/client/echo_api/go/client.go
@@ -460,6 +460,15 @@ func (c *APIClient) decode(v interface{}, b []byte, contentType string) (err err
 		*s = string(b)
 		return nil
 	}
+	if r, ok := v.(*io.Reader); ok {
+		*r = bytes.NewReader(b)
+		return nil
+	}
+	// Must stay before the JSON branch: json.Unmarshal would base64-decode into *[]byte.
+	if p, ok := v.(*[]byte); ok {
+		*p = b
+		return nil
+	}
 	if f, ok := v.(*os.File); ok {
 		f, err = os.CreateTemp("", "HttpClientFile")
 		if err != nil {
diff --git a/samples/client/others/go/allof_multiple_ref_and_discriminator/client.go b/samples/client/others/go/allof_multiple_ref_and_discriminator/client.go
index f797d2c4d2b3..7a19a74088d8 100644
--- a/samples/client/others/go/allof_multiple_ref_and_discriminator/client.go
+++ b/samples/client/others/go/allof_multiple_ref_and_discriminator/client.go
@@ -431,6 +431,15 @@ func (c *APIClient) decode(v interface{}, b []byte, contentType string) (err err
 		*s = string(b)
 		return nil
 	}
+	if r, ok := v.(*io.Reader); ok {
+		*r = bytes.NewReader(b)
+		return nil
+	}
+	// Must stay before the JSON branch: json.Unmarshal would base64-decode into *[]byte.
+	if p, ok := v.(*[]byte); ok {
+		*p = b
+		return nil
+	}
 	if f, ok := v.(*os.File); ok {
 		f, err = os.CreateTemp("", "HttpClientFile")
 		if err != nil {
diff --git a/samples/client/others/go/oneof-anyof-required/client.go b/samples/client/others/go/oneof-anyof-required/client.go
index f797d2c4d2b3..7a19a74088d8 100644
--- a/samples/client/others/go/oneof-anyof-required/client.go
+++ b/samples/client/others/go/oneof-anyof-required/client.go
@@ -431,6 +431,15 @@ func (c *APIClient) decode(v interface{}, b []byte, contentType string) (err err
 		*s = string(b)
 		return nil
 	}
+	if r, ok := v.(*io.Reader); ok {
+		*r = bytes.NewReader(b)
+		return nil
+	}
+	// Must stay before the JSON branch: json.Unmarshal would base64-decode into *[]byte.
+	if p, ok := v.(*[]byte); ok {
+		*p = b
+		return nil
+	}
 	if f, ok := v.(*os.File); ok {
 		f, err = os.CreateTemp("", "HttpClientFile")
 		if err != nil {
diff --git a/samples/client/others/go/oneof-discriminator-lookup/client.go b/samples/client/others/go/oneof-discriminator-lookup/client.go
index f797d2c4d2b3..7a19a74088d8 100644
--- a/samples/client/others/go/oneof-discriminator-lookup/client.go
+++ b/samples/client/others/go/oneof-discriminator-lookup/client.go
@@ -431,6 +431,15 @@ func (c *APIClient) decode(v interface{}, b []byte, contentType string) (err err
 		*s = string(b)
 		return nil
 	}
+	if r, ok := v.(*io.Reader); ok {
+		*r = bytes.NewReader(b)
+		return nil
+	}
+	// Must stay before the JSON branch: json.Unmarshal would base64-decode into *[]byte.
+	if p, ok := v.(*[]byte); ok {
+		*p = b
+		return nil
+	}
 	if f, ok := v.(*os.File); ok {
 		f, err = os.CreateTemp("", "HttpClientFile")
 		if err != nil {
diff --git a/samples/client/petstore/go/go-petstore/client.go b/samples/client/petstore/go/go-petstore/client.go
index 82ace87a5306..85036942f54b 100644
--- a/samples/client/petstore/go/go-petstore/client.go
+++ b/samples/client/petstore/go/go-petstore/client.go
@@ -466,6 +466,15 @@ func (c *APIClient) decode(v interface{}, b []byte, contentType string) (err err
 		*s = string(b)
 		return nil
 	}
+	if r, ok := v.(*io.Reader); ok {
+		*r = bytes.NewReader(b)
+		return nil
+	}
+	// Must stay before the JSON branch: json.Unmarshal would base64-decode into *[]byte.
+	if p, ok := v.(*[]byte); ok {
+		*p = b
+		return nil
+	}
 	if f, ok := v.(*os.File); ok {
 		f, err = os.CreateTemp("", "HttpClientFile")
 		if err != nil {
diff --git a/samples/openapi3/client/extensions/x-auth-id-alias/go-experimental/client.go b/samples/openapi3/client/extensions/x-auth-id-alias/go-experimental/client.go
index 9b0df1df106f..58b26ebc1573 100644
--- a/samples/openapi3/client/extensions/x-auth-id-alias/go-experimental/client.go
+++ b/samples/openapi3/client/extensions/x-auth-id-alias/go-experimental/client.go
@@ -434,6 +434,15 @@ func (c *APIClient) decode(v interface{}, b []byte, contentType string) (err err
 		*s = string(b)
 		return nil
 	}
+	if r, ok := v.(*io.Reader); ok {
+		*r = bytes.NewReader(b)
+		return nil
+	}
+	// Must stay before the JSON branch: json.Unmarshal would base64-decode into *[]byte.
+	if p, ok := v.(*[]byte); ok {
+		*p = b
+		return nil
+	}
 	if f, ok := v.(*os.File); ok {
 		f, err = os.CreateTemp("", "HttpClientFile")
 		if err != nil {
diff --git a/samples/openapi3/client/petstore/go-petstore-generateMarshalJSON-false/client.go b/samples/openapi3/client/petstore/go-petstore-generateMarshalJSON-false/client.go
index 2747d3b9714f..7f611c52fa4d 100644
--- a/samples/openapi3/client/petstore/go-petstore-generateMarshalJSON-false/client.go
+++ b/samples/openapi3/client/petstore/go-petstore-generateMarshalJSON-false/client.go
@@ -446,6 +446,15 @@ func (c *APIClient) decode(v interface{}, b []byte, contentType string) (err err
 		*s = string(b)
 		return nil
 	}
+	if r, ok := v.(*io.Reader); ok {
+		*r = bytes.NewReader(b)
+		return nil
+	}
+	// Must stay before the JSON branch: json.Unmarshal would base64-decode into *[]byte.
+	if p, ok := v.(*[]byte); ok {
+		*p = b
+		return nil
+	}
 	if f, ok := v.(*os.File); ok {
 		f, err = os.CreateTemp("", "HttpClientFile")
 		if err != nil {
diff --git a/samples/openapi3/client/petstore/go-petstore-withXml/client.go b/samples/openapi3/client/petstore/go-petstore-withXml/client.go
index 2747d3b9714f..7f611c52fa4d 100644
--- a/samples/openapi3/client/petstore/go-petstore-withXml/client.go
+++ b/samples/openapi3/client/petstore/go-petstore-withXml/client.go
@@ -446,6 +446,15 @@ func (c *APIClient) decode(v interface{}, b []byte, contentType string) (err err
 		*s = string(b)
 		return nil
 	}
+	if r, ok := v.(*io.Reader); ok {
+		*r = bytes.NewReader(b)
+		return nil
+	}
+	// Must stay before the JSON branch: json.Unmarshal would base64-decode into *[]byte.
+	if p, ok := v.(*[]byte); ok {
+		*p = b
+		return nil
+	}
 	if f, ok := v.(*os.File); ok {
 		f, err = os.CreateTemp("", "HttpClientFile")
 		if err != nil {
diff --git a/samples/openapi3/client/petstore/go/go-petstore-aws-signature/client.go b/samples/openapi3/client/petstore/go/go-petstore-aws-signature/client.go
index 79d1274dfd0c..73c66a0e3188 100644
--- a/samples/openapi3/client/petstore/go/go-petstore-aws-signature/client.go
+++ b/samples/openapi3/client/petstore/go/go-petstore-aws-signature/client.go
@@ -488,6 +488,15 @@ func (c *APIClient) decode(v interface{}, b []byte, contentType string) (err err
 		*s = string(b)
 		return nil
 	}
+	if r, ok := v.(*io.Reader); ok {
+		*r = bytes.NewReader(b)
+		return nil
+	}
+	// Must stay before the JSON branch: json.Unmarshal would base64-decode into *[]byte.
+	if p, ok := v.(*[]byte); ok {
+		*p = b
+		return nil
+	}
 	if f, ok := v.(*os.File); ok {
 		f, err = os.CreateTemp("", "HttpClientFile")
 		if err != nil {
diff --git a/samples/openapi3/client/petstore/go/go-petstore/client.go b/samples/openapi3/client/petstore/go/go-petstore/client.go
index 259fda811873..8f341a904a36 100644
--- a/samples/openapi3/client/petstore/go/go-petstore/client.go
+++ b/samples/openapi3/client/petstore/go/go-petstore/client.go
@@ -484,6 +484,15 @@ func (c *APIClient) decode(v interface{}, b []byte, contentType string) (err err
 		*s = string(b)
 		return nil
 	}
+	if r, ok := v.(*io.Reader); ok {
+		*r = bytes.NewReader(b)
+		return nil
+	}
+	// Must stay before the JSON branch: json.Unmarshal would base64-decode into *[]byte.
+	if p, ok := v.(*[]byte); ok {
+		*p = b
+		return nil
+	}
 	if f, ok := v.(*os.File); ok {
 		f, err = os.CreateTemp("", "HttpClientFile")
 		if err != nil {