diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9f088fad9..51d7e5697 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -59,6 +59,7 @@
 * [#2754](https://github.com/ruby-grape/grape/pull/2754): Merge routing args in place in `Router#process_route` instead of allocating a new Hash via `merge` - [@ericproulx](https://github.com/ericproulx).
 * [#2753](https://github.com/ruby-grape/grape/pull/2753): Lazy-allocate `Grape::Validations::ParamScopeTracker`'s identity-keyed hashes so validating requests that never use the index / qualifying-params trackers allocate no hash - [@ericproulx](https://github.com/ericproulx).
 * [#2752](https://github.com/ruby-grape/grape/pull/2752): Skip per-request `ActiveSupport::Notifications` payload and dispatch when no subscriber is listening, via private `instrument_<event>` guards on `Endpoint`/`Middleware::Formatter` - [@ericproulx](https://github.com/ericproulx).
+* [#2755](https://github.com/ruby-grape/grape/pull/2755): Inline `mustermann-grape` into `Grape::Router::MustermannPattern` and depend on `mustermann` directly - [@ericproulx](https://github.com/ericproulx).
 * [#2757](https://github.com/ruby-grape/grape/pull/2757): Build the `Grape::Cookies` jar only when a cookie is read or written (via a new `Grape::Request#cookies?` predicate gating response-cookie flushing), and drop the jar's now-redundant lazy-parse `Proc` - [@ericproulx](https://github.com/ericproulx).
 * [#2756](https://github.com/ruby-grape/grape/pull/2756): Tighten dependency lower bounds to their compatibility floors (`rack >= 2.2.4`, `zeitwerk >= 2.6`, `dry-configurable >= 1.0`) - [@ericproulx](https://github.com/ericproulx).
 * Your contribution here.
diff --git a/UPGRADING.md b/UPGRADING.md
index 8571c0445..03235066e 100644
--- a/UPGRADING.md
+++ b/UPGRADING.md
@@ -7,6 +7,16 @@ Upgrading Grape
 
 Grape no longer supports Ruby 3.2; 3.3 is now the minimum (`required_ruby_version = '>= 3.3'`). Upgrade your runtime to Ruby 3.3 or newer before bumping Grape.
 
+#### `mustermann-grape` is no longer a dependency
+
+Grape's path-pattern grammar (previously the `mustermann-grape` gem) now lives in Grape itself as `Grape::Router::MustermannPattern`, and Grape depends on `mustermann` directly. This is transparent for normal Grape usage.
+
+The inlined class is no longer registered as a Mustermann type, so if your app called `Mustermann.new(pattern, type: :grape)` and relied on Grape loading `mustermann-grape` for you, add it to your Gemfile explicitly:
+
+```ruby
+gem 'mustermann-grape'
+```
+
 #### `Grape::Exceptions::ValidationErrors.new` keyword renamed `errors:` → `exceptions:`
 
 `Grape::Exceptions::ValidationErrors#initialize` now takes its input array under the `exceptions:` keyword instead of `errors:`. The kwarg accepts a mix of `Grape::Exceptions::Validation` and `Grape::Exceptions::ValidationArrayErrors` instances; `ValidationArrayErrors` wrappers are flattened internally via `flat_map(&:errors)`. The `errors` reader on the constructed instance (the grouped `{params => [Validation, ...]}` Hash) is unchanged.
diff --git a/grape.gemspec b/grape.gemspec
index dbfc51705..7aa0cd177 100644
--- a/grape.gemspec
+++ b/grape.gemspec
@@ -23,7 +23,7 @@ Gem::Specification.new do |s|
   s.add_dependency 'activesupport', '>= 7.2'
   s.add_dependency 'dry-configurable', '>= 1.0'
   s.add_dependency 'dry-types', '>= 1.1'
-  s.add_dependency 'mustermann-grape', '~> 1.1.0'
+  s.add_dependency 'mustermann', '>= 4.0'
   s.add_dependency 'rack', '>= 2.2.4'
   s.add_dependency 'zeitwerk', '>= 2.6'
 
diff --git a/lib/grape.rb b/lib/grape.rb
index f630cc0cb..fdd919e53 100644
--- a/lib/grape.rb
+++ b/lib/grape.rb
@@ -26,7 +26,8 @@
 require 'dry-configurable'
 require 'forwardable'
 require 'json'
-require 'mustermann/grape'
+require 'mustermann'
+require 'mustermann/ast/pattern'
 require 'rack'
 require 'rack/auth/basic'
 require 'rack/builder'
diff --git a/lib/grape/router/mustermann_pattern.rb b/lib/grape/router/mustermann_pattern.rb
new file mode 100644
index 000000000..64891ab09
--- /dev/null
+++ b/lib/grape/router/mustermann_pattern.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+module Grape
+  class Router
+    # Grape-style path patterns for Mustermann: `:param`, `*splat`, `{name}` /
+    # `{+splat}`, `( )` optionals, `|`, and an Integer digit-only constraint
+    # (driven by Grape's `params` option).
+    #
+    # Inlined from the mustermann-grape gem (MIT) by namusyaka, Konstantin Haase
+    # and Daniel Doubrovkine. Grape instantiates this class directly (see
+    # {Grape::Router::Pattern}), so unlike the gem it is not registered as a
+    # Mustermann `type: :grape`.
+    class MustermannPattern < ::Mustermann::AST::Pattern
+      supported_options :params
+
+      on(nil, '?', ')') { |c| unexpected(c) }
+
+      on('*') { |_c| scan(/\w+/) ? node(:named_splat, buffer.matched) : node(:splat) }
+      on(':') do |_c|
+        param_name = scan(/\w+/)
+        # Integer params (declared via Grape's `params` option) match digits only;
+        # any other capture matches a single path segment (anything but / ? # .).
+        param_type = pattern&.options&.dig(:params, param_name, :type)
+        constraint = param_type == 'Integer' ? /\d/ : '[^/?#.]'
+        node(:capture, param_name, constraint:) { scan(/\w+/) }
+      end
+      on('\\') { |_c| node(:char, expect(/./)) }
+      on('(') { |_c| node(:optional, node(:group) { read unless scan(')') }) }
+      on('|') { |_c| node(:or) }
+
+      on('{') do |_c|
+        type = scan('+') ? :named_splat : :capture
+        name = expect(/[\w.]+/)
+        type = :splat if (type == :named_splat) && (name == 'splat')
+        expect('}')
+        node(type, name)
+      end
+
+      suffix('?') do |_c, element|
+        node(:optional, element)
+      end
+    end
+  end
+end
diff --git a/lib/grape/router/pattern.rb b/lib/grape/router/pattern.rb
index 72bc9d617..503cb6488 100644
--- a/lib/grape/router/pattern.rb
+++ b/lib/grape/router/pattern.rb
@@ -16,7 +16,7 @@ class Pattern
       def initialize(origin:, suffix:, anchor:, params:, format:, version:, requirements:)
         @origin = origin
         @path = PatternCache[[build_path_from_pattern(@origin, anchor), suffix]]
-        @pattern = Mustermann::Grape.new(@path, uri_decode: true, params:, capture: extract_capture(format, version, requirements))
+        @pattern = MustermannPattern.new(@path, uri_decode: true, params:, capture: extract_capture(format, version, requirements))
         @to_regexp = @pattern.to_regexp
       end