diff --git a/app/models/concerns/project_api_compatibility.rb b/app/models/concerns/project_api_compatibility.rb
index cb00efb06df..631b2a11e9a 100644
--- a/app/models/concerns/project_api_compatibility.rb
+++ b/app/models/concerns/project_api_compatibility.rb
@@ -9,12 +9,10 @@ module ProjectAPICompatibility
   end
 
   def auto_devops_enabled=(value)
-    self.build_auto_devops if self.auto_devops&.enabled.nil?
-    self.auto_devops.update! enabled: value
+    (auto_devops || build_auto_devops).enabled = value
   end
 
   def auto_devops_deploy_strategy=(value)
-    self.build_auto_devops if self.auto_devops&.enabled.nil?
-    self.auto_devops.update! deploy_strategy: value
+    (auto_devops || build_auto_devops).deploy_strategy = value
   end
 end
diff --git a/app/models/project.rb b/app/models/project.rb
index 2906aca75fc..8dfe2212282 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -277,7 +277,7 @@ class Project < ApplicationRecord
   has_many :project_deploy_tokens
   has_many :deploy_tokens, through: :project_deploy_tokens
 
-  has_one :auto_devops, class_name: 'ProjectAutoDevops'
+  has_one :auto_devops, class_name: 'ProjectAutoDevops', inverse_of: :project, autosave: true
   has_many :custom_attributes, class_name: 'ProjectCustomAttribute'
 
   has_many :project_badges, class_name: 'ProjectBadge'
diff --git a/app/models/project_auto_devops.rb b/app/models/project_auto_devops.rb
index 67c12363a3c..f39f54f0434 100644
--- a/app/models/project_auto_devops.rb
+++ b/app/models/project_auto_devops.rb
@@ -5,7 +5,7 @@ class ProjectAutoDevops < ApplicationRecord
 
   ignore_column :domain
 
-  belongs_to :project
+  belongs_to :project, inverse_of: :auto_devops
 
   enum deploy_strategy: {
     continuous: 0,
diff --git a/changelogs/unreleased/64731-fix-project-auto-devops-api.yml b/changelogs/unreleased/64731-fix-project-auto-devops-api.yml
new file mode 100644
index 00000000000..7fe2c036773
--- /dev/null
+++ b/changelogs/unreleased/64731-fix-project-auto-devops-api.yml
@@ -0,0 +1,5 @@
+---
+title: Fix the project auto devops API
+merge_request: 30946
+author:
+type: fixed
diff --git a/spec/models/concerns/project_api_compatibility_spec.rb b/spec/models/concerns/project_api_compatibility_spec.rb
index 8cecd4fe7bc..f5722f88aac 100644
--- a/spec/models/concerns/project_api_compatibility_spec.rb
+++ b/spec/models/concerns/project_api_compatibility_spec.rb
@@ -16,23 +16,44 @@ describe ProjectAPICompatibility do
     expect(project.build_allow_git_fetch).to eq(false)
   end
 
-  # auto_devops_enabled
-  it "converts auto_devops_enabled=false to auto_devops_enabled?=false" do
-    expect(project.auto_devops_enabled?).to eq(true)
-    project.update!(auto_devops_enabled: false)
-    expect(project.auto_devops_enabled?).to eq(false)
+  describe '#auto_devops_enabled' do
+    where(
+      initial: [:missing, nil, false, true],
+      final: [nil, false, true]
+    )
+
+    with_them do
+      before do
+        project.build_auto_devops(enabled: initial) unless initial == :missing
+      end
+
+      # Implicit auto devops when enabled is nil
+      let(:expected) { final.nil? ? true : final }
+
+      it 'sets the correct value' do
+        project.update!(auto_devops_enabled: final)
+
+        expect(project.auto_devops_enabled?).to eq(expected)
+      end
+    end
   end
 
-  it "converts auto_devops_enabled=true to auto_devops_enabled?=true" do
-    expect(project.auto_devops_enabled?).to eq(true)
-    project.update!(auto_devops_enabled: true)
-    expect(project.auto_devops_enabled?).to eq(true)
-  end
+  describe '#auto_devops_deploy_strategy' do
+    where(
+      initial: [:missing, *ProjectAutoDevops.deploy_strategies.keys],
+      final: ProjectAutoDevops.deploy_strategies.keys
+    )
 
-  # auto_devops_deploy_strategy
-  it "converts auto_devops_deploy_strategy=timed_incremental to auto_devops.deploy_strategy=timed_incremental" do
-    expect(project.auto_devops).to be_nil
-    project.update!(auto_devops_deploy_strategy: 'timed_incremental')
-    expect(project.auto_devops.deploy_strategy).to eq('timed_incremental')
+    with_them do
+      before do
+        project.build_auto_devops(deploy_strategy: initial) unless initial == :missing
+      end
+
+      it 'sets the correct value' do
+        project.update!(auto_devops_deploy_strategy: final)
+
+        expect(project.auto_devops.deploy_strategy).to eq(final)
+      end
+    end
   end
 end