diff --git a/registry/coder/modules/mux/README.md b/registry/coder/modules/mux/README.md
index 2f4155e29..977cbbaad 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 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`. The launcher keeps watching the mux process after startup, appends signal/exit-code diagnostics to the mux log when the server is killed outside the Node runtime, and can optionally wait a few seconds, remove the stale server lock, and restart Mux after any exit until an optional restart-attempt cap is reached. 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/xum) in a Coder workspace. By default, the module auto-detects an available package manager (`npm`, `pnpm`, or `bun`) to install `@coder/xum@next`, the npm package that ships the `mux` CLI (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`. The launcher keeps watching the mux process after startup, appends signal/exit-code diagnostics to the mux log when the server is killed outside the Node runtime, and can optionally wait a few seconds, remove the stale server lock, and restart Mux after any exit until an optional restart-attempt cap is reached. 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  = "1.5.0"
+  version  = "2.0.0"
   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  = "1.5.0"
+  version  = "2.0.0"
   agent_id = coder_agent.main.id
 }
 ```
@@ -48,10 +48,12 @@ module "mux" {
 module "mux" {
   count    = data.coder_workspace.me.start_count
   source   = "registry.coder.com/coder/mux/coder"
-  version  = "1.5.0"
+  version  = "2.0.0"
   agent_id = coder_agent.main.id
-  # Default is "latest"; set to a specific version to pin
-  install_version = "0.4.0"
+  # Default is "next"; set to a specific version to pin.
+  # Only versions published as @coder/xum are available: 0.28.3 or newer,
+  # or prereleases from 0.28.2-next.24.
+  install_version = "0.28.4"
 }
 ```
 
@@ -63,7 +65,7 @@ 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     = "1.5.0"
+  version     = "2.0.0"
   agent_id    = coder_agent.main.id
   add_project = "/path/to/project"
 }
@@ -78,7 +80,7 @@ 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              = "1.5.0"
+  version              = "2.0.0"
   agent_id             = coder_agent.main.id
   additional_arguments = "--open-mode pinned --add-project '/workspaces/my repo'"
 }
@@ -92,7 +94,7 @@ Enable automatic restarts after Mux exits, including clean exits and intentional
 module "mux" {
   count                 = data.coder_workspace.me.start_count
   source                = "registry.coder.com/coder/mux/coder"
-  version               = "1.5.0"
+  version               = "2.0.0"
   agent_id              = coder_agent.main.id
   restart_on_kill       = true
   restart_delay_seconds = 3
@@ -106,7 +108,7 @@ module "mux" {
 module "mux" {
   count    = data.coder_workspace.me.start_count
   source   = "registry.coder.com/coder/mux/coder"
-  version  = "1.5.0"
+  version  = "2.0.0"
   agent_id = coder_agent.main.id
   port     = 8080
 }
@@ -120,7 +122,7 @@ Force a specific package manager instead of auto-detection:
 module "mux" {
   count           = data.coder_workspace.me.start_count
   source          = "registry.coder.com/coder/mux/coder"
-  version         = "1.5.0"
+  version         = "2.0.0"
   agent_id        = coder_agent.main.id
   package_manager = "pnpm" # or "npm", "bun"
 }
@@ -128,13 +130,13 @@ module "mux" {
 
 ### Custom Registry
 
-Use a private or mirrored npm registry:
+Use a private or mirrored npm registry. The registry must serve the scoped `@coder/xum` package:
 
 ```tf
 module "mux" {
   count        = data.coder_workspace.me.start_count
   source       = "registry.coder.com/coder/mux/coder"
-  version      = "1.5.0"
+  version      = "2.0.0"
   agent_id     = coder_agent.main.id
   registry_url = "https://npm.pkg.github.com"
 }
@@ -148,7 +150,7 @@ 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    = "1.5.0"
+  version    = "2.0.0"
   agent_id   = coder_agent.main.id
   use_cached = true
 }
@@ -156,13 +158,13 @@ module "mux" {
 
 ### Skip Install
 
-Run without installing from the network (requires Mux to be pre-installed):
+Run without installing from the network (requires a `mux` binary at `<install_prefix>/mux`, by default `~/.coder-modules/coder/mux/mux`):
 
 ```tf
 module "mux" {
   count    = data.coder_workspace.me.start_count
   source   = "registry.coder.com/coder/mux/coder"
-  version  = "1.5.0"
+  version  = "2.0.0"
   agent_id = coder_agent.main.id
   install  = false
 }
@@ -177,8 +179,10 @@ module "mux" {
 - Mux is currently in preview and you may encounter bugs
 - Requires internet connectivity for agent operations (unless `install` is set to false)
 - Auto-detects `npm`, `pnpm`, or `bun` by default; set `package_manager` to force a specific one
-- Requires a Node.js runtime; if `node` is not on the workspace `PATH`, the module bootstraps a pinned Node.js runtime into `~/.local/share/coder-mux` (override the version with the `MUX_NODE_VERSION` environment variable)
-- Installs `mux@next` from the npm registry by default; set `registry_url` to use a private or mirrored registry
+- Requires a Node.js runtime; if `node` is not on the workspace `PATH`, the module bootstraps a pinned Node.js runtime into `~/.coder-modules/coder/mux` (override the version with the `MUX_NODE_VERSION` environment variable)
+- Installs `@coder/xum@next` from the npm registry by default (this package ships the `mux` binary); set `registry_url` to use a private or mirrored registry
+- `install_version` must be a version or dist-tag published as `@coder/xum` (0.28.3 or newer, or a prerelease from 0.28.2-next.24); older releases were only published under the legacy `mux` package name
+- Installs into `~/.coder-modules/coder/mux` and logs to `~/.coder-modules/coder/mux/logs/mux.log` by default, so the install survives restarts that clear `/tmp`; override with `install_prefix` and `log_path`
 - Falls back to a direct tarball download when no package manager is found
 - Appends best-effort signal and external-kill diagnostics to `log_path` if the mux process dies after startup
 - Set `restart_on_kill = true` to wait `restart_delay_seconds`, remove `~/.mux/server.lock`, and restart Mux after it exits
diff --git a/registry/coder/modules/mux/main.test.ts b/registry/coder/modules/mux/main.test.ts
index a8944deec..7d26cebb5 100644
--- a/registry/coder/modules/mux/main.test.ts
+++ b/registry/coder/modules/mux/main.test.ts
@@ -1,6 +1,5 @@
 import { describe, expect, it } from "bun:test";
 import {
-  executeScriptInContainer,
   execContainer,
   findResourceInstance,
   readFileContainer,
@@ -8,9 +7,38 @@ import {
   runContainer,
   runTerraformApply,
   runTerraformInit,
+  type scriptOutput,
+  type TerraformState,
   testRequiredVariables,
 } from "~test";
 
+// Default install_prefix and log_path with HOME=/root inside the test containers.
+const MODULE_ROOT = "/root/.coder-modules/coder/mux";
+const LOG_PATH = `${MODULE_ROOT}/logs/mux.log`;
+
+// Like executeScriptInContainer, but removes the container inside the test:
+// deleting a container that holds a full @coder/xum install takes longer than
+// the few seconds the global afterAll cleanup hook allows.
+const executeInstallScriptInContainer = async (
+  state: TerraformState,
+  image: string,
+  before: string,
+): Promise<scriptOutput> => {
+  const instance = findResourceInstance(state, "coder_script");
+  const id = await runContainer(image);
+  try {
+    await execContainer(id, ["sh", "-c", before]);
+    const resp = await execContainer(id, ["sh", "-c", instance.script]);
+    return {
+      exitCode: resp.exitCode,
+      stdout: resp.stdout.trim().split("\n"),
+      stderr: resp.stderr.trim().split("\n"),
+    };
+  } finally {
+    await removeContainer(id);
+  }
+};
+
 describe("mux", async () => {
   await runTerraformInit(import.meta.dir);
 
@@ -23,10 +51,9 @@ describe("mux", async () => {
       agent_id: "foo",
     });
 
-    const output = await executeScriptInContainer(
+    const output = await executeInstallScriptInContainer(
       state,
       "alpine/curl",
-      "sh",
       "apk add --no-cache bash tar gzip ca-certificates findutils nodejs && update-ca-certificates",
     );
     if (output.exitCode !== 0) {
@@ -36,9 +63,9 @@ describe("mux", async () => {
     expect(output.exitCode).toBe(0);
     const expectedLines = [
       "📥 No package manager found; downloading tarball from registry...",
-      "🥳 mux has been installed in /tmp/mux",
+      `🥳 mux has been installed in ${MODULE_ROOT}`,
       "🚀 Starting mux server on port 4000...",
-      "Check logs at /tmp/mux.log!",
+      `Check logs at ${LOG_PATH}!`,
     ];
     for (const line of expectedLines) {
       expect(output.stdout).toContain(line);
@@ -49,7 +76,6 @@ describe("mux", async () => {
     const state = await runTerraformApply(import.meta.dir, {
       agent_id: "foo",
       install: false,
-      log_path: "/tmp/mux.log",
       additional_arguments:
         "--open-mode pinned --add-project '/workspaces/my repo'",
     });
@@ -62,8 +88,8 @@ describe("mux", async () => {
         "sh",
         "-c",
         `apk add --no-cache bash >/dev/null
-mkdir -p /tmp/mux
-cat <<'EOF' > /tmp/mux/mux
+mkdir -p ${MODULE_ROOT}
+cat <<'EOF' > ${MODULE_ROOT}/mux
 #!/usr/bin/env sh
 i=1
 for arg in "$@"; do
@@ -71,7 +97,7 @@ for arg in "$@"; do
   i=$((i + 1))
 done
 EOF
-chmod +x /tmp/mux/mux`,
+chmod +x ${MODULE_ROOT}/mux`,
       ]);
       expect(setup.exitCode).toBe(0);
 
@@ -83,7 +109,7 @@ chmod +x /tmp/mux/mux`,
       expect(output.exitCode).toBe(0);
 
       await execContainer(id, ["sh", "-c", "sleep 1"]);
-      const log = await readFileContainer(id, "/tmp/mux.log");
+      const log = await readFileContainer(id, LOG_PATH);
       expect(log).toContain("arg1=server");
       expect(log).toContain("arg2=--port");
       expect(log).toContain("arg3=4000");
@@ -100,7 +126,6 @@ chmod +x /tmp/mux/mux`,
     const state = await runTerraformApply(import.meta.dir, {
       agent_id: "foo",
       install: false,
-      log_path: "/tmp/mux.log",
     });
 
     const instance = findResourceInstance(state, "coder_script");
@@ -111,8 +136,8 @@ chmod +x /tmp/mux/mux`,
         "sh",
         "-c",
         `apk add --no-cache bash >/dev/null
-mkdir -p /tmp/mux
-cat <<'EOF' > /tmp/mux/mux
+mkdir -p ${MODULE_ROOT}
+cat <<'EOF' > ${MODULE_ROOT}/mux
 #!/usr/bin/env sh
 target_pid="$$"
 (
@@ -123,7 +148,7 @@ while true; do
   sleep 1
 done
 EOF
-chmod +x /tmp/mux/mux`,
+chmod +x ${MODULE_ROOT}/mux`,
       ]);
       expect(setup.exitCode).toBe(0);
 
@@ -135,7 +160,7 @@ chmod +x /tmp/mux/mux`,
       expect(output.exitCode).toBe(0);
 
       await execContainer(id, ["sh", "-c", "sleep 2"]);
-      const log = await readFileContainer(id, "/tmp/mux.log");
+      const log = await readFileContainer(id, LOG_PATH);
       expect(log).toContain("shell exit code 137");
       expect(log).toContain(
         "SIGKILL usually means the process was killed externally or by the OOM killer.",
@@ -149,7 +174,6 @@ chmod +x /tmp/mux/mux`,
     const state = await runTerraformApply(import.meta.dir, {
       agent_id: "foo",
       install: false,
-      log_path: "/tmp/mux.log",
       restart_on_kill: true,
       restart_delay_seconds: 1,
       max_restart_attempts: 1,
@@ -163,10 +187,10 @@ chmod +x /tmp/mux/mux`,
         "sh",
         "-c",
         `apk add --no-cache bash >/dev/null
-mkdir -p /tmp/mux
-cat <<'EOF' > /tmp/mux/mux
+mkdir -p ${MODULE_ROOT}
+cat <<'EOF' > ${MODULE_ROOT}/mux
 #!/usr/bin/env sh
-run_count_file="/tmp/mux-run-count"
+run_count_file="${MODULE_ROOT}/run-count"
 run_count=0
 if [ -f "$run_count_file" ]; then
   run_count=$(cat "$run_count_file")
@@ -186,7 +210,7 @@ else
 fi
 exit 0
 EOF
-chmod +x /tmp/mux/mux`,
+chmod +x ${MODULE_ROOT}/mux`,
       ]);
       expect(setup.exitCode).toBe(0);
 
@@ -198,8 +222,8 @@ chmod +x /tmp/mux/mux`,
       expect(output.exitCode).toBe(0);
 
       await execContainer(id, ["sh", "-c", "sleep 4"]);
-      const log = await readFileContainer(id, "/tmp/mux.log");
-      const runCount = await readFileContainer(id, "/tmp/mux-run-count");
+      const log = await readFileContainer(id, LOG_PATH);
+      const runCount = await readFileContainer(id, `${MODULE_ROOT}/run-count`);
       expect(log).toContain("run=1");
       expect(log).toContain("mux server exited cleanly.");
       expect(log).toContain(
@@ -223,7 +247,6 @@ chmod +x /tmp/mux/mux`,
     const state = await runTerraformApply(import.meta.dir, {
       agent_id: "foo",
       install: false,
-      log_path: "/tmp/mux.log",
       restart_on_kill: true,
       restart_delay_seconds: 1,
       max_restart_attempts: 1,
@@ -237,10 +260,10 @@ chmod +x /tmp/mux/mux`,
         "sh",
         "-c",
         `apk add --no-cache bash >/dev/null
-mkdir -p /tmp/mux
-cat <<'EOF' > /tmp/mux/mux
+mkdir -p ${MODULE_ROOT}
+cat <<'EOF' > ${MODULE_ROOT}/mux
 #!/usr/bin/env sh
-run_count_file="/tmp/mux-run-count"
+run_count_file="${MODULE_ROOT}/run-count"
 run_count=0
 if [ -f "$run_count_file" ]; then
   run_count=$(cat "$run_count_file")
@@ -253,7 +276,7 @@ if [ "$run_count" -eq 1 ]; then
 fi
 exit 0
 EOF
-chmod +x /tmp/mux/mux`,
+chmod +x ${MODULE_ROOT}/mux`,
       ]);
       expect(setup.exitCode).toBe(0);
 
@@ -265,8 +288,8 @@ chmod +x /tmp/mux/mux`,
       expect(output.exitCode).toBe(0);
 
       await execContainer(id, ["sh", "-c", "sleep 4"]);
-      const log = await readFileContainer(id, "/tmp/mux.log");
-      const runCount = await readFileContainer(id, "/tmp/mux-run-count");
+      const log = await readFileContainer(id, LOG_PATH);
+      const runCount = await readFileContainer(id, `${MODULE_ROOT}/run-count`);
       expect(log).toContain("run=1");
       expect(log).toContain("signal TERM (15); shell exit code 143.");
       expect(log).toContain(
@@ -287,20 +310,19 @@ chmod +x /tmp/mux/mux`,
       agent_id: "foo",
     });
 
-    const output = await executeScriptInContainer(
+    const output = await executeInstallScriptInContainer(
       state,
       "node:20-alpine",
-      "sh",
       "apk add bash",
     );
 
     expect(output.exitCode).toBe(0);
     const expectedLines = [
-      "📦 Installing mux via npm into /tmp/mux...",
+      `📦 Installing @coder/xum via npm into ${MODULE_ROOT}...`,
       "⏭️  Skipping lifecycle scripts with --ignore-scripts",
-      "🥳 mux has been installed in /tmp/mux",
+      `🥳 mux has been installed in ${MODULE_ROOT}`,
       "🚀 Starting mux server on port 4000...",
-      "Check logs at /tmp/mux.log!",
+      `Check logs at ${LOG_PATH}!`,
     ];
     for (const line of expectedLines) {
       expect(output.stdout).toContain(line);
diff --git a/registry/coder/modules/mux/main.tf b/registry/coder/modules/mux/main.tf
index f80b8b3ff..787df6934 100644
--- a/registry/coder/modules/mux/main.tf
+++ b/registry/coder/modules/mux/main.tf
@@ -39,14 +39,14 @@ variable "slug" {
 
 variable "install_prefix" {
   type        = string
-  description = "The prefix to install Mux to."
-  default     = "/tmp/mux"
+  description = "The directory to install Mux into."
+  default     = "$HOME/.coder-modules/coder/mux"
 }
 
 variable "log_path" {
   type        = string
   description = "The path for Mux logs."
-  default     = "/tmp/mux.log"
+  default     = "$HOME/.coder-modules/coder/mux/logs/mux.log"
 }
 
 variable "restart_on_kill" {
@@ -91,7 +91,7 @@ variable "additional_arguments" {
 
 variable "install_version" {
   type        = string
-  description = "The version or dist-tag of Mux to install."
+  description = "The version or dist-tag of the @coder/xum npm package to install. Only versions published as @coder/xum are available: 0.28.3 or newer, or prereleases from 0.28.2-next.24."
   default     = "next"
 }
 
@@ -107,7 +107,7 @@ variable "package_manager" {
 
 variable "registry_url" {
   type        = string
-  description = "The npm-compatible registry URL to install Mux from. Override this for private registries or mirrors."
+  description = "The npm-compatible registry URL to install @coder/xum from. Override this for private registries or mirrors."
   default     = "https://registry.npmjs.org"
 }
 
diff --git a/registry/coder/modules/mux/mux.tftest.hcl b/registry/coder/modules/mux/mux.tftest.hcl
index af4cbfe23..4a0db7edc 100644
--- a/registry/coder/modules/mux/mux.tftest.hcl
+++ b/registry/coder/modules/mux/mux.tftest.hcl
@@ -221,7 +221,7 @@ run "custom_version" {
 
   variables {
     agent_id        = "foo"
-    install_version = "0.3.0"
+    install_version = "0.28.4"
   }
 }
 
@@ -245,6 +245,87 @@ run "use_cached_only_success" {
   }
 }
 
+# Module-controlled paths default to the per-module root (AGENTS.md Module
+# Data Layout) so the install and logs survive restarts that clear /tmp.
+run "default_paths_under_module_root" {
+  command = plan
+
+  variables {
+    agent_id = "foo"
+  }
+
+  assert {
+    condition     = strcontains(resource.coder_script.mux.script, "MUX_BINARY=\"$HOME/.coder-modules/coder/mux/mux\"")
+    error_message = "mux must install under $HOME/.coder-modules/coder/mux by default"
+  }
+
+  assert {
+    condition     = strcontains(resource.coder_script.mux.script, "LOG_PATH=\"$HOME/.coder-modules/coder/mux/logs/mux.log\"")
+    error_message = "mux must log to $HOME/.coder-modules/coder/mux/logs/mux.log by default"
+  }
+
+  assert {
+    condition     = strcontains(resource.coder_script.mux.script, "node_dir=\"$HOME/.coder-modules/coder/mux/node-v")
+    error_message = "the Node.js bootstrap must live under the module root"
+  }
+
+  assert {
+    condition     = !strcontains(resource.coder_script.mux.script, "/tmp/mux")
+    error_message = "mux script must not default any module path to /tmp"
+  }
+}
+
+run "custom_install_prefix_and_log_path" {
+  command = plan
+
+  variables {
+    agent_id       = "foo"
+    install_prefix = "/opt/mux"
+    log_path       = "/var/log/mux.log"
+  }
+
+  assert {
+    condition     = strcontains(resource.coder_script.mux.script, "MUX_BINARY=\"/opt/mux/mux\"")
+    error_message = "mux must honor a custom install_prefix"
+  }
+
+  assert {
+    condition     = strcontains(resource.coder_script.mux.script, "LOG_PATH=\"/var/log/mux.log\"")
+    error_message = "mux must honor a custom log_path"
+  }
+}
+
+# The installed npm package must be @coder/xum (it ships the mux bin);
+# the legacy mux package is only a compat shim with an exact-pinned
+# @coder/xum dependency that is published separately.
+run "installs_coder_xum_package" {
+  command = plan
+
+  variables {
+    agent_id = "foo"
+  }
+
+  assert {
+    condition     = strcontains(resource.coder_script.mux.script, "PKG=\"@coder/xum\"")
+    error_message = "mux script must install the @coder/xum npm package"
+  }
+
+  assert {
+    condition     = strcontains(resource.coder_script.mux.script, "https://registry.npmjs.org/@coder%2Fxum/")
+    error_message = "tarball fallback must fetch @coder/xum metadata with the URL-encoded scoped name"
+  }
+
+  assert {
+    condition     = strcontains(resource.coder_script.mux.script, "https://registry.npmjs.org/@coder/xum/-/xum-")
+    error_message = "tarball fallback must construct the scoped @coder/xum tarball URL"
+  }
+
+  assert {
+    condition     = !strcontains(resource.coder_script.mux.script, "PKG=\"mux\"")
+    error_message = "mux script must not install the legacy mux compat package"
+  }
+}
+
 # Custom package_manager should appear in generated script
 run "custom_package_manager_npm" {
   command = plan
@@ -332,7 +413,7 @@ run "registry_url_trailing_slash" {
   }
 
   assert {
-    condition     = strcontains(resource.coder_script.mux.script, "https://npm.example.com/mux/")
+    condition     = strcontains(resource.coder_script.mux.script, "https://npm.example.com/@coder%2Fxum/")
     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 04431e02f..839a07c21 100644
--- a/registry/coder/modules/mux/run.sh
+++ b/registry/coder/modules/mux/run.sh
@@ -196,7 +196,7 @@ EOF_LAUNCHER
 }
 # Ensure a Node.js runtime is available (mux is a Node application launched
 # via "#!/usr/bin/env node"). When the workspace image does not provide node,
-# bootstrap a pinned runtime into $HOME so it persists across restarts.
+# bootstrap a pinned runtime into the module root so it persists across restarts.
 ensure_node() {
   if command -v node > /dev/null 2>&1; then
     return 0
@@ -213,7 +213,7 @@ ensure_node() {
       ;;
   esac
 
-  node_dir="$HOME/.local/share/coder-mux/node-v$node_version-linux-$node_arch"
+  node_dir="$HOME/.coder-modules/coder/mux/node-v$node_version-linux-$node_arch"
   if [ ! -x "$node_dir/bin/node" ]; then
     echo "⚠️ node not found on PATH; bootstrapping Node.js v$node_version into $node_dir..."
     mkdir -p "$(dirname "$node_dir")"
@@ -272,8 +272,11 @@ if [ ! -f "$MUX_BINARY" ] || [ "${USE_CACHED}" != true ]; then
     fi
   fi
 
+  # @coder/xum is the package that ships the mux CLI (bins: mux, xum).
+  PKG="@coder/xum"
+
   if [ -n "$PM_CMD" ]; then
-    echo "📦 Installing mux via $PM_CMD into ${INSTALL_PREFIX}..."
+    echo "📦 Installing $PKG via $PM_CMD into ${INSTALL_PREFIX}..."
     NPM_WORKDIR="${INSTALL_PREFIX}/npm"
     mkdir -p "$NPM_WORKDIR"
     cd "$NPM_WORKDIR" || exit 1
@@ -281,7 +284,6 @@ if [ ! -f "$MUX_BINARY" ] || [ "${USE_CACHED}" != true ]; then
       echo '{}' > package.json
     fi
     echo "⏭️  Skipping lifecycle scripts with --ignore-scripts"
-    PKG="mux"
     if [ -z "${VERSION}" ] || [ "${VERSION}" = "latest" ]; then
       PKG_SPEC="$PKG@latest"
     else
@@ -306,7 +308,7 @@ if [ ! -f "$MUX_BINARY" ] || [ "${USE_CACHED}" != true ]; then
         ;;
     esac
     if [ "$INSTALL_OK" != true ]; then
-      echo "❌ Failed to install mux via $PM_CMD"
+      echo "❌ Failed to install $PKG via $PM_CMD"
       exit 1
     fi
     # Determine the installed binary path
@@ -324,7 +326,8 @@ if [ ! -f "$MUX_BINARY" ] || [ "${USE_CACHED}" != true ]; then
     if [ -z "$VERSION_TO_USE" ]; then
       VERSION_TO_USE="next"
     fi
-    META_URL="${REGISTRY_URL}/mux/$VERSION_TO_USE"
+    # Scoped package names are URL-encoded in npm registry metadata paths.
+    META_URL="${REGISTRY_URL}/@coder%2Fxum/$VERSION_TO_USE"
     META_JSON="$(curl -fsSL "$META_URL" || true)"
     if [ -z "$META_JSON" ]; then
       echo "❌ Failed to fetch npm metadata: $META_URL"
@@ -360,10 +363,11 @@ if [ ! -f "$MUX_BINARY" ] || [ "${USE_CACHED}" != true ]; then
         VERSION_TO_USE="$RESOLVED_VERSION"
       fi
       if [ -z "$VERSION_TO_USE" ]; then
-        echo "❌ Could not determine version for mux"
+        echo "❌ Could not determine version for $PKG"
         exit 1
       fi
-      TARBALL_URL="${REGISTRY_URL}/mux/-/mux-$VERSION_TO_USE.tgz"
+      # Registry tarball layout for scoped packages: /@scope/name/-/name-<version>.tgz
+      TARBALL_URL="${REGISTRY_URL}/@coder/xum/-/xum-$VERSION_TO_USE.tgz"
     fi
     TMP_DIR="$(mktemp -d)"
     TAR_PATH="$TMP_DIR/mux.tgz"