diff --git a/registry/coder/modules/mux/README.md b/registry/coder/modules/mux/README.md
index 69073926..eacf005a 100644
--- a/registry/coder/modules/mux/README.md
+++ b/registry/coder/modules/mux/README.md
@@ -8,13 +8,13 @@ tags: [ai, agents, development, multiplexer]
 
 # Mux
 
-Automatically install and run [Mux](https://github.com/coder/mux) in a Coder workspace. By default, the module installs `mux@next` from npm (with a fallback to downloading the npm tarball if npm is unavailable). Mux is a desktop application for parallel agentic development that enables developers to run multiple AI agents simultaneously across isolated workspaces.
+Automatically install and run [Mux](https://github.com/coder/mux) in a Coder workspace. By default, the module auto-detects an available package manager (`npm`, `pnpm`, or `bun`) to install `mux@next` (with a fallback to downloading the npm tarball if none is found). You can also force a specific package manager via `package_manager` and point to a custom registry with `registry_url`. Mux is a desktop application for parallel agentic development that enables developers to run multiple AI agents simultaneously across isolated workspaces.
 
 ```tf
 module "mux" {
   count    = data.coder_workspace.me.start_count
   source   = "registry.coder.com/coder/mux/coder"
-  version  = "1.2.0"
+  version  = "1.3.0"
   agent_id = coder_agent.main.id
 }
 ```
@@ -37,7 +37,7 @@ module "mux" {
 module "mux" {
   count    = data.coder_workspace.me.start_count
   source   = "registry.coder.com/coder/mux/coder"
-  version  = "1.2.0"
+  version  = "1.3.0"
   agent_id = coder_agent.main.id
 }
 ```
@@ -48,7 +48,7 @@ module "mux" {
 module "mux" {
   count    = data.coder_workspace.me.start_count
   source   = "registry.coder.com/coder/mux/coder"
-  version  = "1.2.0"
+  version  = "1.3.0"
   agent_id = coder_agent.main.id
   # Default is "latest"; set to a specific version to pin
   install_version = "0.4.0"
@@ -63,7 +63,7 @@ Start Mux with `mux server --add-project /path/to/project`:
 module "mux" {
   count       = data.coder_workspace.me.start_count
   source      = "registry.coder.com/coder/mux/coder"
-  version     = "1.2.0"
+  version     = "1.3.0"
   agent_id    = coder_agent.main.id
   add-project = "/path/to/project"
 }
@@ -78,7 +78,7 @@ The module parses quoted values, so grouped arguments remain intact.
 module "mux" {
   count                = data.coder_workspace.me.start_count
   source               = "registry.coder.com/coder/mux/coder"
-  version              = "1.2.0"
+  version              = "1.3.0"
   agent_id             = coder_agent.main.id
   additional_arguments = "--open-mode pinned --add-project '/workspaces/my repo'"
 }
@@ -90,12 +90,40 @@ module "mux" {
 module "mux" {
   count    = data.coder_workspace.me.start_count
   source   = "registry.coder.com/coder/mux/coder"
-  version  = "1.2.0"
+  version  = "1.3.0"
   agent_id = coder_agent.main.id
   port     = 8080
 }
 ```
 
+### Custom Package Manager
+
+Force a specific package manager instead of auto-detection:
+
+```tf
+module "mux" {
+  count           = data.coder_workspace.me.start_count
+  source          = "registry.coder.com/coder/mux/coder"
+  version         = "1.3.0"
+  agent_id        = coder_agent.main.id
+  package_manager = "pnpm" # or "npm", "bun"
+}
+```
+
+### Custom Registry
+
+Use a private or mirrored npm registry:
+
+```tf
+module "mux" {
+  count        = data.coder_workspace.me.start_count
+  source       = "registry.coder.com/coder/mux/coder"
+  version      = "1.3.0"
+  agent_id     = coder_agent.main.id
+  registry_url = "https://npm.pkg.github.com"
+}
+```
+
 ### Use Cached Installation
 
 Run an existing copy of Mux if found, otherwise install from npm:
@@ -104,7 +132,7 @@ Run an existing copy of Mux if found, otherwise install from npm:
 module "mux" {
   count      = data.coder_workspace.me.start_count
   source     = "registry.coder.com/coder/mux/coder"
-  version    = "1.2.0"
+  version    = "1.3.0"
   agent_id   = coder_agent.main.id
   use_cached = true
 }
@@ -118,7 +146,7 @@ Run without installing from the network (requires Mux to be pre-installed):
 module "mux" {
   count    = data.coder_workspace.me.start_count
   source   = "registry.coder.com/coder/mux/coder"
-  version  = "1.2.0"
+  version  = "1.3.0"
   agent_id = coder_agent.main.id
   install  = false
 }
@@ -132,4 +160,6 @@ module "mux" {
 
 - Mux is currently in preview and you may encounter bugs
 - Requires internet connectivity for agent operations (unless `install` is set to false)
-- Installs `mux@next` from npm by default (falls back to the npm tarball if npm is unavailable)
+- Auto-detects `npm`, `pnpm`, or `bun` by default; set `package_manager` to force a specific one
+- Installs `mux@next` from the npm registry by default; set `registry_url` to use a private or mirrored registry
+- Falls back to a direct tarball download when no package manager is found
diff --git a/registry/coder/modules/mux/main.test.ts b/registry/coder/modules/mux/main.test.ts
index c1b6e238..cc2e70db 100644
--- a/registry/coder/modules/mux/main.test.ts
+++ b/registry/coder/modules/mux/main.test.ts
@@ -35,7 +35,7 @@ describe("mux", async () => {
     }
     expect(output.exitCode).toBe(0);
     const expectedLines = [
-      "📥 npm not found; downloading tarball from npm registry...",
+      "📥 No package manager found; downloading tarball from registry...",
       "🥳 mux has been installed in /tmp/mux",
       "🚀 Starting mux server on port 4000...",
       "Check logs at /tmp/mux.log!",
@@ -111,7 +111,7 @@ chmod +x /tmp/mux/mux`,
     expect(output.exitCode).toBe(0);
     const expectedLines = [
       "📦 Installing mux via npm into /tmp/mux...",
-      "⏭️  Skipping npm lifecycle scripts with --ignore-scripts",
+      "⏭️  Skipping lifecycle scripts with --ignore-scripts",
       "🥳 mux has been installed in /tmp/mux",
       "🚀 Starting mux server on port 4000...",
       "Check logs at /tmp/mux.log!",
diff --git a/registry/coder/modules/mux/main.tf b/registry/coder/modules/mux/main.tf
index dbc585d8..7ca97ccc 100644
--- a/registry/coder/modules/mux/main.tf
+++ b/registry/coder/modules/mux/main.tf
@@ -67,6 +67,23 @@ variable "install_version" {
   default     = "next"
 }
 
+variable "package_manager" {
+  type        = string
+  description = "Package manager to install Mux. 'auto' detects npm, pnpm, or bun (falling back to tarball download). Set to 'npm', 'pnpm', or 'bun' to force a specific one."
+  default     = "auto"
+  validation {
+    condition     = contains(["auto", "npm", "pnpm", "bun"], var.package_manager)
+    error_message = "The 'package_manager' variable must be one of: 'auto', 'npm', 'pnpm', 'bun'."
+  }
+}
+
+variable "registry_url" {
+  type        = string
+  description = "The npm-compatible registry URL to install Mux from. Override this for private registries or mirrors."
+  default     = "https://registry.npmjs.org"
+}
+
+
 variable "share" {
   type    = string
   default = "owner"
@@ -137,6 +154,7 @@ resource "random_password" "mux_auth_token" {
 
 locals {
   mux_auth_token = random_password.mux_auth_token.result
+  registry_url   = trimsuffix(var.registry_url, "/")
 }
 
 resource "coder_script" "mux" {
@@ -153,6 +171,8 @@ resource "coder_script" "mux" {
     OFFLINE : !var.install,
     USE_CACHED : var.use_cached,
     AUTH_TOKEN : local.mux_auth_token,
+    PACKAGE_MANAGER : var.package_manager,
+    REGISTRY_URL : local.registry_url,
   })
   run_on_start = true
 
diff --git a/registry/coder/modules/mux/mux.tftest.hcl b/registry/coder/modules/mux/mux.tftest.hcl
index 688ddedb..42569997 100644
--- a/registry/coder/modules/mux/mux.tftest.hcl
+++ b/registry/coder/modules/mux/mux.tftest.hcl
@@ -121,3 +121,96 @@ run "use_cached_only_success" {
     use_cached = true
   }
 }
+
+# Custom package_manager should appear in generated script
+run "custom_package_manager_npm" {
+  command = plan
+
+  variables {
+    agent_id        = "foo"
+    package_manager = "npm"
+  }
+
+  assert {
+    condition     = strcontains(resource.coder_script.mux.script, "PM_CMD=\"npm\"")
+    error_message = "mux script must set PM_CMD to the configured package manager"
+  }
+}
+
+run "custom_package_manager_pnpm" {
+  command = plan
+
+  variables {
+    agent_id        = "foo"
+    package_manager = "pnpm"
+  }
+
+  assert {
+    condition     = strcontains(resource.coder_script.mux.script, "PM_CMD=\"pnpm\"")
+    error_message = "mux script must set PM_CMD to the configured package manager"
+  }
+}
+
+run "custom_package_manager_bun" {
+  command = plan
+
+  variables {
+    agent_id        = "foo"
+    package_manager = "bun"
+  }
+
+  assert {
+    condition     = strcontains(resource.coder_script.mux.script, "PM_CMD=\"bun\"")
+    error_message = "mux script must set PM_CMD to the configured package manager"
+  }
+}
+
+# Invalid package_manager should fail validation
+run "invalid_package_manager" {
+  command = plan
+
+  variables {
+    agent_id        = "foo"
+    package_manager = "yarn"
+  }
+
+  expect_failures = [
+    var.package_manager
+  ]
+}
+
+# Custom registry_url should appear in generated script
+run "custom_registry_url" {
+  command = plan
+
+  variables {
+    agent_id     = "foo"
+    registry_url = "https://npm.example.com"
+  }
+
+  assert {
+    condition     = strcontains(resource.coder_script.mux.script, "https://npm.example.com")
+    error_message = "mux script must use the configured registry URL"
+  }
+
+  assert {
+    condition     = !strcontains(resource.coder_script.mux.script, "registry.npmjs.org")
+    error_message = "mux script must not contain hardcoded registry.npmjs.org when custom registry is set"
+  }
+}
+
+# registry_url trailing slash should be stripped
+run "registry_url_trailing_slash" {
+  command = plan
+
+  variables {
+    agent_id     = "foo"
+    registry_url = "https://npm.example.com/"
+  }
+
+  assert {
+    condition     = strcontains(resource.coder_script.mux.script, "https://npm.example.com/mux/")
+    error_message = "registry URL trailing slash must be stripped to avoid double slashes"
+  }
+}
+
diff --git a/registry/coder/modules/mux/run.sh b/registry/coder/modules/mux/run.sh
index 099448fb..2dbd5ea9 100644
--- a/registry/coder/modules/mux/run.sh
+++ b/registry/coder/modules/mux/run.sh
@@ -54,7 +54,7 @@ fi
 
 # If there is no cached install OR we don't want to use a cached install
 if [ ! -f "$MUX_BINARY" ] || [ "${USE_CACHED}" != true ]; then
-  printf "$${BOLD}Installing mux from npm...\n"
+  printf "$${BOLD}Installing mux...\n"
 
   # Clean up from other install (in case install prefix changed).
   if [ -n "$CODER_SCRIPT_BIN_DIR" ] && [ -e "$CODER_SCRIPT_BIN_DIR/mux" ]; then
@@ -63,41 +63,76 @@ if [ ! -f "$MUX_BINARY" ] || [ "${USE_CACHED}" != true ]; then
 
   mkdir -p "$(dirname "$MUX_BINARY")"
 
-  if command -v npm > /dev/null 2>&1; then
-    echo "📦 Installing mux via npm into ${INSTALL_PREFIX}..."
+  # Determine which package manager to use
+  PM_CMD=""
+  if [ "${PACKAGE_MANAGER}" = "auto" ]; then
+    for pm in npm pnpm bun; do
+      if command -v "$pm" > /dev/null 2>&1; then
+        PM_CMD="$pm"
+        break
+      fi
+    done
+  else
+    PM_CMD="${PACKAGE_MANAGER}"
+    if ! command -v "$PM_CMD" > /dev/null 2>&1; then
+      echo "❌ Configured package manager '${PACKAGE_MANAGER}' not found on PATH"
+      exit 1
+    fi
+  fi
+
+  if [ -n "$PM_CMD" ]; then
+    echo "📦 Installing mux via $PM_CMD into ${INSTALL_PREFIX}..."
     NPM_WORKDIR="${INSTALL_PREFIX}/npm"
     mkdir -p "$NPM_WORKDIR"
     cd "$NPM_WORKDIR" || exit 1
     if [ ! -f package.json ]; then
       echo '{}' > package.json
     fi
-    echo "⏭️  Skipping npm lifecycle scripts with --ignore-scripts"
+    echo "⏭️  Skipping lifecycle scripts with --ignore-scripts"
     PKG="mux"
     if [ -z "${VERSION}" ] || [ "${VERSION}" = "latest" ]; then
       PKG_SPEC="$PKG@latest"
     else
       PKG_SPEC="$PKG@${VERSION}"
     fi
-    if ! npm install --no-audit --no-fund --omit=dev --ignore-scripts "$PKG_SPEC"; then
-      echo "❌ Failed to install mux via npm"
+    INSTALL_OK=true
+    case "$PM_CMD" in
+      npm)
+        if ! npm install --no-audit --no-fund --omit=dev --ignore-scripts --registry "${REGISTRY_URL}" "$PKG_SPEC"; then
+          INSTALL_OK=false
+        fi
+        ;;
+      pnpm)
+        if ! pnpm add --ignore-scripts --registry "${REGISTRY_URL}" "$PKG_SPEC"; then
+          INSTALL_OK=false
+        fi
+        ;;
+      bun)
+        if ! bun add --ignore-scripts --registry "${REGISTRY_URL}" "$PKG_SPEC"; then
+          INSTALL_OK=false
+        fi
+        ;;
+    esac
+    if [ "$INSTALL_OK" != true ]; then
+      echo "❌ Failed to install mux via $PM_CMD"
       exit 1
     fi
     # Determine the installed binary path
     BIN_DIR="$NPM_WORKDIR/node_modules/.bin"
     CANDIDATE="$BIN_DIR/mux"
     if [ ! -f "$CANDIDATE" ]; then
-      echo "❌ Could not locate mux binary after npm install"
+      echo "❌ Could not locate mux binary after $PM_CMD install"
       exit 1
     fi
     chmod +x "$CANDIDATE" || true
     ln -sf "$CANDIDATE" "$MUX_BINARY"
   else
-    echo "📥 npm not found; downloading tarball from npm registry..."
+    echo "📥 No package manager found; downloading tarball from registry..."
     VERSION_TO_USE="${VERSION}"
     if [ -z "$VERSION_TO_USE" ]; then
       VERSION_TO_USE="next"
     fi
-    META_URL="https://registry.npmjs.org/mux/$VERSION_TO_USE"
+    META_URL="${REGISTRY_URL}/mux/$VERSION_TO_USE"
     META_JSON="$(curl -fsSL "$META_URL" || true)"
     if [ -z "$META_JSON" ]; then
       echo "❌ Failed to fetch npm metadata: $META_URL"
@@ -136,7 +171,7 @@ if [ ! -f "$MUX_BINARY" ] || [ "${USE_CACHED}" != true ]; then
         echo "❌ Could not determine version for mux"
         exit 1
       fi
-      TARBALL_URL="https://registry.npmjs.org/mux/-/mux-$VERSION_TO_USE.tgz"
+      TARBALL_URL="${REGISTRY_URL}/mux/-/mux-$VERSION_TO_USE.tgz"
     fi
     TMP_DIR="$(mktemp -d)"
     TAR_PATH="$TMP_DIR/mux.tgz"