diff --git a/sdk/go/README.md b/sdk/go/README.md
index 130c397f2..8962b6317 100644
--- a/sdk/go/README.md
+++ b/sdk/go/README.md
@@ -198,11 +198,15 @@ sb, err := client.Create(ctx, cubesandbox.CreateOptions{
 When `CUBE_PROXY_NODE_IP` is set, data-plane requests connect directly to that IP and port while preserving the virtual sandbox host:
 
 ```text
-URL:  <CUBE_PROXY_SCHEME>://49999-<sandboxID>.<CUBE_SANDBOX_DOMAIN>/<envd-endpoint>
+URL:  <CUBE_PROXY_SCHEME>://49983-<sandboxID>.<CUBE_SANDBOX_DOMAIN>/<envd-endpoint>
 TCP:  <CUBE_PROXY_NODE_IP>:<CUBE_PROXY_PORT_HTTP>
-Host: 49999-<sandboxID>.<CUBE_SANDBOX_DOMAIN>
+Host: 49983-<sandboxID>.<CUBE_SANDBOX_DOMAIN>
 ```
 
+The host prefix is the sandbox's internal service port: `49983` (envd) for
+commands/filesystem/files/PTY, and `49999` (Jupyter) for the code interpreter
+(`RunCode` / `/execute`).
+
 You can also set it directly:
 
 ```go
diff --git a/sdk/go/envd.go b/sdk/go/envd.go
index 72810ddfc..886bac678 100644
--- a/sdk/go/envd.go
+++ b/sdk/go/envd.go
@@ -225,7 +225,7 @@ func multipartFileBody(path string, data []byte) (io.Reader, string, error) {
 func (s *Sandbox) newEnvdRequest(ctx context.Context, method, path string, query url.Values, body io.Reader) (*http.Request, error) {
 	target := url.URL{
 		Scheme:   s.client.config.ProxyScheme,
-		Host:     s.GetHost(JupyterPort),
+		Host:     s.GetHost(EnvdPort),
 		Path:     path,
 		RawQuery: query.Encode(),
 	}
diff --git a/sdk/go/sandbox.go b/sdk/go/sandbox.go
index 07ff27d46..0acc2e32a 100644
--- a/sdk/go/sandbox.go
+++ b/sdk/go/sandbox.go
@@ -13,7 +13,15 @@ import (
 	"time"
 )
 
-const JupyterPort = 49999
+const (
+	// JupyterPort is the code-interpreter (Jupyter) port, used only by the
+	// /execute endpoint (RunCode).
+	JupyterPort = 49999
+	// EnvdPort is the envd daemon port. All envd data-plane RPCs — commands,
+	// filesystem, files, and PTY — route here, matching the Python/Node SDKs
+	// (ENVD_PORT = 49983). Sending these to JupyterPort yields 404s.
+	EnvdPort = 49983
+)
 
 func (s *Sandbox) GetHost(port int) string {
 	domain := s.Domain
diff --git a/sdk/go/sdk_test.go b/sdk/go/sdk_test.go
index 0599e61f0..fa36529c6 100644
--- a/sdk/go/sdk_test.go
+++ b/sdk/go/sdk_test.go
@@ -655,7 +655,7 @@ func TestCommandsRunUsesEnvdProcessStart(t *testing.T) {
 		t.Fatalf("Run: %v", err)
 	}
 
-	if gotHost != "49999-sb-proc.cube.test" {
+	if gotHost != "49983-sb-proc.cube.test" {
 		t.Fatalf("Host=%q", gotHost)
 	}
 	if gotHeaders.Get("Content-Type") != connectContentType || gotHeaders.Get("Connect-Protocol-Version") != connectProtocolVersion {
@@ -721,7 +721,7 @@ func TestFilesReadUsesEnvdHTTPFileAPI(t *testing.T) {
 	if content != "file content" {
 		t.Fatalf("content=%q", content)
 	}
-	if gotHost != "49999-sb-files.cube.test" || gotPath != "/tmp/foo bar.txt" || gotToken != "envd-token" {
+	if gotHost != "49983-sb-files.cube.test" || gotPath != "/tmp/foo bar.txt" || gotToken != "envd-token" {
 		t.Fatalf("host/path/token=%q/%q/%q", gotHost, gotPath, gotToken)
 	}
 }
@@ -944,7 +944,7 @@ func TestFilesListUsesEnvdFilesystemRPC(t *testing.T) {
 	if len(entries) != 1 || entries[0].Name != "a.txt" || entries[0].Size != 10 || entries[0].IsDir() {
 		t.Fatalf("entries=%#v", entries)
 	}
-	if gotHost != "49999-sb-fs.cube.test" || gotPath != "/filesystem.Filesystem/ListDir" || gotCT != "application/json" {
+	if gotHost != "49983-sb-fs.cube.test" || gotPath != "/filesystem.Filesystem/ListDir" || gotCT != "application/json" {
 		t.Fatalf("host/path/ct=%q/%q/%q", gotHost, gotPath, gotCT)
 	}
 }