diff --git a/config.ru b/config.ru
index 4e95b1d7..f3272ca3 100644
--- a/config.ru
+++ b/config.ru
@@ -25,7 +25,7 @@ use Travis::Web::ApiRedirect do |app|
   app.settings.api_endpoint = ENV['API_ENDPOINT'] if ENV['API_ENDPOINT']
 end
 
-run Travis::Web::App.new(
+run Travis::Web::App.build(
   environment:  ENV['RACK_ENV'] || 'development',
   api_endpoint: ENV['API_ENDPOINT'],
   pusher_key:   ENV['PUSHER_KEY'],
diff --git a/lib/travis/web/app.rb b/lib/travis/web/app.rb
index da5f475b..6ec4f3df 100644
--- a/lib/travis/web/app.rb
+++ b/lib/travis/web/app.rb
@@ -8,6 +8,8 @@ require 'time'
 class Travis::Web::App
   autoload :MobileRedirect, 'travis/web/app/mobile_redirect'
 
+  S3_URL = 'https://s3.amazonaws.com/travis-web-production/assets'
+
   # Simple Rack router that behaves like a hash.
   # Key is the path, value the response.
   class Router < DelegateClass(Hash)
@@ -18,90 +20,110 @@ class Travis::Web::App
     end
 
     def call(env)
-      if main_app.custom_branch?(env)
-        main_app.response_for_custom_branch(env)
-      else
-        self[env['PATH_INFO']]
-      end
+      self[env['PATH_INFO']]
     end
   end
 
-  def self.new(options = {})
-    return super unless options[:environment] == 'development'
-    proc { |e| super.call(e) } # poor man's reloader
+  class AltVersions
+    attr_reader :app
+
+    def initialize(app)
+      @app = app
+    end
+
+    def call(env)
+      alt = alt_from(env)
+      env['travis.alt'] = alt if alt
+      status, headers, body = app.call(env)
+      set_cookies(headers, env['travis.alt']) if env.key?('travis.alt')
+      [status, headers, body]
+    end
+
+    def set_cookies(headers, alt)
+      headers['Set-Cookie'] = "alt=#{alt}; Max-Age=#{alt == 'default' ? 0 : 86400}"
+    end
+
+    def alt_from(env)
+      alt_from_params(env) || alt_from_cookie(env)
+    end
+
+    def alt_from_params(env)
+      alt_from_string env['QUERY_STRING']
+    end
+
+    def alt_from_cookie(env)
+      alt_from_string env['HTTP_COOKIE']
+    end
+
+    def alt_from_string(string)
+      $1 if string =~ /alt=([^&]*)/
+    end
   end
 
-  attr_reader :app, :router, :environment, :version, :last_modified, :age, :options, :root
+  class << self
+    def new(options = {})
+      return super unless options[:environment] == 'development'
+      proc { |e| super.call(e) } # poor man's reloader
+    end
+
+    def build(options = {})
+      builder = Rack::Builder.new
+      if options.fetch(:environment) == 'production'
+        builder.use Rack::SSL
+        builder.use Rack::Cache
+      end
+      builder.use Rack::Deflater
+      builder.use Rack::Head
+      builder.use Rack::Protection::XSSHeader
+      builder.use Rack::Protection::FrameOptions
+      builder.use Rack::Protection::PathTraversal
+      builder.use Rack::ConditionalGet
+      builder.use Travis::Web::App::AltVersions
+      builder.run new(options)
+      builder.to_app
+    end
+  end
+
+  attr_reader :routers, :environment, :version, :last_modified, :age, :options, :root
 
   def initialize(options = {})
     @options       = options
     @environment   = options.fetch(:environment)
     @root          = options.fetch(:root)
-    @router        = Router.new(self)
-    @app           = builder.to_app
     @version       = File.read File.expand_path('version', root)
     @last_modified = Time.now
     @age           = 60 * 60 * 24 * 365
-    load_routes
+    @routers       = { default: create_router }
   end
 
   def call(env)
-    app.call(env)
-  end
-
-  def response_for_custom_branch(env)
-    status, headers, body = response_for File.join(root, 'index.html'), custom_branch: custom_branch(env)
-    response = Rack::Response.new body, status, headers
-
-    if disable_custom_branch?(env)
-      response.delete_cookie 'custom_branch'
-    elsif custom_branch_from_params(env)
-      response.set_cookie 'custom_branch', value: custom_branch_from_params(env), expires: Time.now + 31536000
-    end
-
-    response.finish
-  end
-
-  def custom_branch?(env)
-    custom_branch(env) || disable_custom_branch?(env)
+    name = env['travis.alt'] || :default
+    routers[name] ||= create_router(alt: name)
+    routers[name].call(env)
   end
 
   private
 
-    def disable_custom_branch?(env)
-      env['QUERY_STRING'] =~ /disable[_-]custom[_-]branch/
+    def create_router(options = {})
+      router = Router.new(self)
+      load_routes(router, options)
+      router
     end
 
-    def custom_branch_from_params(env)
-      branch = custom_branch_from_string env['QUERY_STRING']
-    end
-
-    def custom_branch_from_cookie(env)
-      custom_branch_from_string env['HTTP_COOKIE']
-    end
-
-    def custom_branch_from_string(string)
-      $1 if string =~ /(?<!disable.)custom[_-]branch=([^&]+)/
-    end
-
-    def custom_branch(env)
-      custom_branch_from_params(env) || custom_branch_from_cookie(env)
-    end
-
-    def load_routes
-      each_file { |f| router[route_for(f)] = response_for(f) }
+    def load_routes(router, options = {})
+      each_file { |file| router[path_for(file)] = response_for(file, options) }
       router.default = router['/']
     end
 
     def response_for(file, options = {})
       content = File.read(file)
-      set_config(content, options) if config_needed? file
+      set_config(content, options) if config_needed?(file)
 
       headers = {
         'Content-Length'   => content.bytesize.to_s,
-        'Content-Location' => route_for(file),
+        'Content-Location' => path_for(file),
         'Cache-Control'    => cache_control(file),
-        'Content-Location' => route_for(file),
+        'Content-Location' => path_for(file),
         'Content-Type'     => mime_type(file),
         'ETag'             => version,
         'Last-Modified'    => last_modified.httpdate,
@@ -109,7 +131,7 @@ class Travis::Web::App
         'Vary'             => vary_for(file)
       }
 
-      [ 200, headers, [ content ] ]
+      [ 200, headers, [content] ]
     end
 
     def each_file
@@ -126,18 +148,11 @@ class Travis::Web::App
     end
 
     def index?(file)
-      file.end_with? 'index.html'
-    end
-
-    def route_for(file)
-      file = file.sub("#{root}/", '')
-      file = File.join(version, file) if prefix? file
-      file = "" if index? file
-      "/#{file}"
+      file.end_with?('index.html')
     end
 
     def cache_control(file)
-      case route_for(file)
+      case path_for(file)
       when '/'        then "public, must-revalidate"
       when '/version' then "no-cache"
       else "public, max-age=#{age}"
@@ -145,13 +160,20 @@ class Travis::Web::App
     end
 
     def vary_for(file)
-      case route_for(file)
+      case path_for(file)
       when '/'         then 'Accept'
       when '/version'  then '*'
       else ''
       end
     end
 
+    def path_for(file)
+      file = file.sub("#{root}/", '')
+      file = File.join(version, file) if prefix?(file)
+      file = "" if index?(file)
+      "/#{file}"
+    end
+
     def mime_type(file)
       Rack::Mime.mime_type File.extname(file)
     end
@@ -162,28 +184,7 @@ class Travis::Web::App
       end
 
       string.gsub! %r{(src|href)="(?:\/?)((styles|scripts)\/[^"]*)"} do
-        if opts[:custom_branch]
-          url = "https://s3.amazonaws.com/travis-web-production/assets/#{opts[:custom_branch]}/#{$2}"
-          %(#$1="#{url}")
-        else
-          %(#$1="/#{version}/#$2")
-        end
+        %(#{$1}=#{opts[:alt] ? "#{S3_URL}/#{opts[:alt]}/#{$2}" : "/#{version}/#{$2}"})
       end
     end
-
-    def builder
-      builder = Rack::Builder.new
-      if environment == 'production'
-        builder.use Rack::SSL
-        builder.use Rack::Cache
-      end
-      builder.use Rack::Deflater
-      builder.use Rack::Head
-      builder.use Rack::Protection::XSSHeader
-      builder.use Rack::Protection::FrameOptions
-      builder.use Rack::Protection::PathTraversal
-      builder.use Rack::ConditionalGet
-      builder.run router
-      builder
-    end
 end
diff --git a/spec/app_spec.rb b/spec/app_spec.rb
index 584616ba..b50f687a 100644
--- a/spec/app_spec.rb
+++ b/spec/app_spec.rb
@@ -6,7 +6,7 @@ describe Travis::Web::App do
   end
 
   describe 'catch all' do
-    before { get('/foo/bar') }
+    before  { get('/foo/bar') }
     example { last_response.should be_ok }
     example { headers['Content-Location'].should be == '/' }
     example { headers['Cache-Control'].should include('must-revalidate') }
@@ -15,7 +15,7 @@ describe Travis::Web::App do
   end
 
   describe 'assets' do
-    before { get('/favicon.ico') }
+    before  { get('/favicon.ico') }
     example { last_response.should be_ok }
     example { headers['Content-Location'].should be == '/favicon.ico' }
     example { headers['Cache-Control'].should_not include('must-revalidate') }
@@ -24,30 +24,30 @@ describe Travis::Web::App do
   end
 
   describe 'version' do
-    before { get('/version') }
+    before  { get('/version') }
     example { last_response.should be_ok }
     example { headers['Content-Location'].should be == '/version' }
     example { headers['Cache-Control'].should be == 'no-cache' }
     example { headers['Vary'].split(',').should_not include('Accept') }
   end
 
-  describe 'custom branch' do
-    context 'when passing custom branch as a param' do
-      before { get('/?custom-branch=foo') }
+  describe 'alternate asset versions' do
+    context 'not passing an alt param' do
+      before  { get('/') }
+      example { headers['Set-Cookie'].should be_nil }
+    end
+
+    context 'passing an alt param' do
+      before  { get('/?alt=foo') }
       example { last_response.should be_ok }
       example { last_response.body.should include('/assets/foo/styles/app.css') }
       example { last_response.body.should include('/assets/foo/scripts/app.js') }
-      example { headers['Set-Cookie'].should include('custom_branch=foo') }
+      example { headers['Set-Cookie'].should == 'alt=foo; Max-Age=86400' }
     end
 
-    context 'disabling custom branch' do
-      before { get('/?disable-custom-branch=true') }
-      example { last_response.should be_ok }
-      example { last_response.body.should =~ %r{src="/[^\/]+/scripts/app.js} }
-      example { last_response.body.should_not include('/assets/true/styles/app.css') }
-      example { last_response.body.should_not include('/assets/foo/styles/app.css') }
-      example { last_response.body.should_not include('/assets/foo/scripts/app.js') }
-      example { headers['Set-Cookie'].should include('custom_branch=;') }
+    context 'passing default as an alt param' do
+      before  { get('/?alt=default') }
+      example { headers['Set-Cookie'].should == 'alt=default; Max-Age=0' }
     end
   end
 end