diff --git a/CLAUDE.md b/CLAUDE.md
index 4f8bc13..52d4600 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -19,7 +19,8 @@ Hako is a Docker container management tool designed specifically for Claude Code
 - Container names follow pattern: `hako-{language}-{project}-{subdirs}` (sanitized, max 60 chars)
 - All Docker commands are logged to stderr for transparency
 - File syncing respects .gitignore and excludes .git directory for security
-- Images are versioned (HAKO-VERSION=1) for upgrade management
+- Images are versioned (HAKO-VERSION=1, as a Docker label) for upgrade management
+  - NOTE: changes to the base Dockerfiles should involve bumping the hako version
 
 ## Development Commands
 
@@ -44,4 +45,4 @@ go build -o hako
 
 - Base Dockerfile stored in `~/.config/hako/Dockerfile.base`
 - Language Dockerfiles in `~/.config/hako/Dockerfile.{lang}`
-- Mounts Claude config directory/file if present for seamless integration
\ No newline at end of file
+- Mounts Claude config directory/file if present for seamless integration
diff --git a/commands.go b/commands.go
index d061eac..41d17f1 100644
--- a/commands.go
+++ b/commands.go
@@ -19,6 +19,9 @@ func initCommand(lang string) error {
 		if err := buildBaseImage(); err != nil {
 			return err
 		}
+	} else {
+		// Check base image version
+		checkVersionMismatch("hako-userland")
 	}
 
 	fmt.Printf("Building %s language image...\n", lang)
@@ -36,6 +39,9 @@ func upCommand(lang string) error {
 		return fmt.Errorf("image %s not found, run 'hako init %s' first", imageName, lang)
 	}
 
+	// Check for version mismatch
+	checkVersionMismatch(imageName)
+
 	cwd, err := os.Getwd()
 	if err != nil {
 		return err
@@ -103,7 +109,24 @@ func downCommand(container string) error {
 
 func psCommand() error {
 	fmt.Println("Hako containers:")
-	return listHakoContainers()
+	if err := listHakoContainers(); err != nil {
+		return err
+	}
+
+	// Check for version mismatches in running containers
+	output, err := runCommandOutput("docker", "ps", "-a", "--filter", "name=hako-", "--format", "{{.Image}}")
+	if err == nil {
+		images := strings.Split(strings.TrimSpace(output), "\n")
+		checkedImages := make(map[string]bool)
+		for _, image := range images {
+			if image != "" && !checkedImages[image] {
+				checkVersionMismatch(image)
+				checkedImages[image] = true
+			}
+		}
+	}
+
+	return nil
 }
 
 func syncCommand() error {
@@ -122,7 +145,7 @@ func syncCommand() error {
 	}
 
 	fmt.Printf("Syncing files from container %s...\n", containerName)
-	
+
 	tempDir, err := os.MkdirTemp("", "hako-sync-*")
 	if err != nil {
 		return err
@@ -184,12 +207,12 @@ func copyWorkspaceToContainer(containerName string) error {
 	if err != nil {
 		return err
 	}
-	
+
 	untrackedFiles, err := runCommandOutput("git", "ls-files", "--others", "--exclude-standard")
 	if err != nil {
 		return err
 	}
-	
+
 	allFiles := []string{}
 	if trackedFiles != "" {
 		allFiles = append(allFiles, strings.Split(trackedFiles, "\n")...)
@@ -197,17 +220,17 @@ func copyWorkspaceToContainer(containerName string) error {
 	if untrackedFiles != "" {
 		allFiles = append(allFiles, strings.Split(untrackedFiles, "\n")...)
 	}
-	
+
 	if len(allFiles) == 0 {
 		return fmt.Errorf("no files to copy")
 	}
-	
+
 	// Copy files one by one to preserve directory structure
 	for _, file := range allFiles {
 		if file == "" {
 			continue
 		}
-		
+
 		// Create directory structure in container if needed
 		dir := filepath.Dir(file)
 		if dir != "." {
@@ -215,12 +238,12 @@ func copyWorkspaceToContainer(containerName string) error {
 				return err
 			}
 		}
-		
+
 		// Copy the file
 		if err := copyToContainer(containerName, file, "/workspace/"+file); err != nil {
 			return fmt.Errorf("failed to copy %s: %v", file, err)
 		}
 	}
-	
+
 	return nil
-}
\ No newline at end of file
+}
diff --git a/docker.go b/docker.go
index 4aef59a..6faea18 100644
--- a/docker.go
+++ b/docker.go
@@ -28,8 +28,8 @@ func ensureConfigDir() error {
 }
 
 func getBaseDockerfile() string {
-	return fmt.Sprintf(`# HAKO-VERSION=%s
-FROM debian:trixie-20250610
+	return fmt.Sprintf(`FROM debian:trixie-20250610
+LABEL HAKO-VERSION=%s
 
 RUN apt-get update && apt-get install -y \
     curl \
@@ -57,17 +57,17 @@ CMD ["/usr/bin/fish"]`, hakoVersion)
 func getLanguageDockerfile(lang string) string {
 	switch lang {
 	case "go":
-		return fmt.Sprintf(`# HAKO-VERSION=%s
-FROM hako-userland
+		return fmt.Sprintf(`FROM hako-userland
+LABEL HAKO-VERSION=%s
 
 RUN curl -fsSL https://go.dev/dl/go1.21.5.linux-amd64.tar.gz | tar -C /usr/local -xzf -
 ENV PATH="/usr/local/go/bin:${PATH}"
 
 WORKDIR /workspace
-CMD ["/bin/bash"]`, hakoVersion)
+CMD ["/usr/bin/fish"]`, hakoVersion)
 	case "py", "python":
-		return fmt.Sprintf(`# HAKO-VERSION=%s
-FROM hako-userland
+		return fmt.Sprintf(`FROM hako-userland
+LABEL HAKO-VERSION=%s
 
 RUN apt-get update && apt-get install -y \
     python3 \
@@ -78,7 +78,7 @@ RUN apt-get update && apt-get install -y \
 RUN ln -s /usr/bin/python3 /usr/bin/python
 
 WORKDIR /workspace
-CMD ["/bin/bash"]`, hakoVersion)
+CMD ["/usr/bin/fish"]`, hakoVersion)
 	default:
 		return ""
 	}
@@ -148,7 +148,6 @@ func createContainer(containerName, imageName, workspaceDir string) error {
 	// Mount workspace
 	args = append(args, "-v", workspaceDir+":/workspace")
 
-
 	args = append(args, "-it", imageName)
 
 	if err := runCommand("docker", args...); err != nil {
@@ -206,3 +205,24 @@ func copyFromContainer(containerName, srcPath, destPath string) error {
 func listHakoContainers() error {
 	return runCommand("docker", "ps", "-a", "--filter", "name=hako-", "--format", "table {{.Names}}\\t{{.Status}}\\t{{.Image}}")
 }
+
+func getImageVersion(imageName string) (string, error) {
+	output, err := runCommandOutput("docker", "image", "inspect", "-f", "{{index .Config.Labels \"HAKO-VERSION\"}}", imageName)
+	if err != nil {
+		return "", err
+	}
+	return strings.TrimSpace(output), nil
+}
+
+func checkVersionMismatch(imageName string) {
+	imageVersion, err := getImageVersion(imageName)
+	if err != nil {
+		// If we can't get the version, don't warn (might be old image without version)
+		return
+	}
+
+	if imageVersion != "" && imageVersion != hakoVersion {
+		fmt.Printf("\033[33mWarning: Image %s has version %s but hako executable is version %s\033[0m\n", imageName, imageVersion, hakoVersion)
+		fmt.Printf("\033[33mConsider running 'hako init' to rebuild with the current version\033[0m\n")
+	}
+}
diff --git a/git.go b/git.go
index b98a706..537267d 100644
--- a/git.go
+++ b/git.go
@@ -41,7 +41,7 @@ func getProjectContainerName(lang string) (string, error) {
 	}
 
 	projectName := filepath.Base(gitRoot)
-	
+
 	var pathComponents []string
 	if relPath != "." {
 		pathComponents = strings.Split(relPath, string(os.PathSeparator))
@@ -65,4 +65,4 @@ func sanitizeName(name string) string {
 	result = strings.ReplaceAll(result, ".", "_")
 	result = strings.ReplaceAll(result, "-", "_")
 	return result
-}
\ No newline at end of file
+}
diff --git a/main.go b/main.go
index 05ecf82..86f4f83 100644
--- a/main.go
+++ b/main.go
@@ -96,4 +96,4 @@ func main() {
 	if err := rootCmd.Execute(); err != nil {
 		os.Exit(1)
 	}
-}
\ No newline at end of file
+}
diff --git a/utils.go b/utils.go
index ca62b74..65508f9 100644
--- a/utils.go
+++ b/utils.go
@@ -24,12 +24,3 @@ func runCommandOutput(name string, args ...string) (string, error) {
 	}
 	return strings.TrimSpace(string(output)), nil
 }
-
-func runCommandWithInput(name string, input string, args ...string) error {
-	cmd := exec.Command(name, args...)
-	fmt.Fprintf(os.Stderr, "+ %s %s\n", name, strings.Join(args, " "))
-	cmd.Stdin = strings.NewReader(input)
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	return cmd.Run()
-}
\ No newline at end of file