diff --git a/.github/workflows/cd.yml b/.github/workflows/cd.yml
index 07a80fb..87285c1 100644
--- a/.github/workflows/cd.yml
+++ b/.github/workflows/cd.yml
@@ -43,7 +43,7 @@
   
         - uses: ruby/setup-ruby@v1
           with:
-            ruby-version: "3.4"
+            ruby-version-file: .ruby-version
 
         - uses: oxidize-rb/actions/cross-gem@v1
           id: cross-gem
@@ -88,7 +88,7 @@
   
         - uses: oxidize-rb/actions/setup-ruby-and-rust@v1
           with:
-            ruby-version: "3.4"
+            ruby-version-file: .ruby-version
             bundler-cache: true
             cargo-cache: false
   
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index ad553f9..376d949 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -40,6 +40,22 @@ jobs:
         run: bundle exec rake
       - name: Compile rust ext
         run: bundle exec rake compile:release
+
+  rspec_ruby_version_file:
+    name: "RSpec (ruby-version-file)"
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: oxidize-rb/actions/setup-ruby-and-rust@v1
+        with:
+          ruby-version-file: .ruby-version
+          rustup-toolchain: stable
+          bundler-cache: true
+          cargo-cache: false
+      - name: Run ruby tests
+        run: bundle exec rake
+      - name: Compile rust ext
+        run: bundle exec rake compile:release
   static_type_check:
     name: "Type Check"
     runs-on: ubuntu-latest
@@ -49,7 +65,7 @@ jobs:
         uses: ruby/setup-ruby@v1
         with:
           bundler-cache: true
-          ruby-version: 3.3
+          ruby-version-file: .ruby-version
       - name: Run static type checks
         run: bundle exec srb tc
   notify_on_failure:
diff --git a/.gitignore b/.gitignore
index 93bf3b3..8cafb89 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,6 +9,11 @@
 /target/
 /vendor
 
+# Locally-built native extensions (installed into versioned directories)
+# Keep this narrowly scoped so we don't accidentally ignore real Ruby source dirs
+# like lib/code_ownership/private/.
+/lib/code_ownership/[0-9]*.[0-9]*/
+
 Gemfile.lock
 
 # rspec failure tracking
diff --git a/.rubocop.yml b/.rubocop.yml
index 6f345ad..4a24fc7 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -12,6 +12,8 @@ AllCops:
   NewCops: enable
   Exclude:
     - vendor/bundle/**/**
+    - tmp/**/**
+    - target/**/**
   TargetRubyVersion: 3.2
 
 Metrics/ParameterLists:
diff --git a/.ruby-version b/.ruby-version
index 4f5e697..1454f6e 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-3.4.5
+4.0.1
diff --git a/code_ownership.gemspec b/code_ownership.gemspec
index 282940c..8b27e9d 100644
--- a/code_ownership.gemspec
+++ b/code_ownership.gemspec
@@ -21,7 +21,7 @@ Gem::Specification.new do |spec|
           'public gem pushes.'
   end
 
-  spec.required_ruby_version = '>= 3.2'
+  spec.required_ruby_version = Gem::Requirement.new('>= 3.2', '< 4.1.dev')
 
   # https://guides.rubygems.org/make-your-own-gem/#adding-an-executable
   # and
diff --git a/ext/code_ownership/extconf.rb b/ext/code_ownership/extconf.rb
index 60ca23a..d15d818 100644
--- a/ext/code_ownership/extconf.rb
+++ b/ext/code_ownership/extconf.rb
@@ -3,7 +3,8 @@
 require 'mkmf'
 require 'rb_sys/mkmf'
 
-create_rust_makefile('code_ownership/code_ownership') do |ext|
+ruby_minor = RUBY_VERSION[/\d+\.\d+/]
+create_rust_makefile("code_ownership/#{ruby_minor}/code_ownership") do |ext|
   ext.extra_cargo_args += ['--crate-type', 'cdylib']
   ext.extra_cargo_args += ['--package', 'code_ownership']
 end
diff --git a/lib/code_ownership/version.rb b/lib/code_ownership/version.rb
index 1b99d6e..4b66e08 100644
--- a/lib/code_ownership/version.rb
+++ b/lib/code_ownership/version.rb
@@ -2,5 +2,5 @@
 # frozen_string_literal: true
 
 module CodeOwnership
-  VERSION = '2.1.0'
+  VERSION = '2.1.1'
 end
diff --git a/rakelib/compile.rake b/rakelib/compile.rake
index e8a3e11..ee9efa9 100644
--- a/rakelib/compile.rake
+++ b/rakelib/compile.rake
@@ -1,5 +1,6 @@
 require 'rb_sys/extensiontask'
 
 RbSys::ExtensionTask.new('code_ownership', GEMSPEC) do |ext|
-  ext.lib_dir = 'lib/code_ownership'
+  ruby_minor = RUBY_VERSION[/\d+\.\d+/]
+  ext.lib_dir = "lib/code_ownership/#{ruby_minor}"
 end
diff --git a/sorbet/config b/sorbet/config
index 26caf17..f5e49d9 100644
--- a/sorbet/config
+++ b/sorbet/config
@@ -1,3 +1,5 @@
 --dir=.
 --ignore=/spec
+--ignore=/tmp
+--ignore=/target
 --ignore=/vendor/bundle