diff --git a/app/grpc/flow_handler.rb b/app/grpc/flow_handler.rb
index 1ab0deb7..05f004fd 100644
--- a/app/grpc/flow_handler.rb
+++ b/app/grpc/flow_handler.rb
@@ -9,14 +9,12 @@ class FlowHandler < Tucana::Sagittarius::FlowService::Service
 
   def self.update_runtime(runtime)
     flows = []
-    runtime.projects.each do |project|
-      project.flows.each do |flow|
+    runtime.project_assignments.compatible.each do |assignment|
+      assignment.project.flows.each do |flow|
         flows << flow.to_grpc
       end
     end
 
-    # TODO: Add check to check for primary runtime conflicts
-
     send_update(
       Tucana::Sagittarius::FlowResponse.new(
         flows: Tucana::Shared::Flows.new(
diff --git a/app/jobs/update_runtime_compatibility_job.rb b/app/jobs/update_runtime_compatibility_job.rb
new file mode 100644
index 00000000..21c6c63f
--- /dev/null
+++ b/app/jobs/update_runtime_compatibility_job.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+class UpdateRuntimeCompatibilityJob < ApplicationJob
+  def perform(conditions)
+    assignments = NamespaceProjectRuntimeAssignment.where(conditions)
+
+    assignments.each do |assignment|
+      res = Runtimes::CheckRuntimeCompatibilityService.new(assignment.runtime, assignment.namespace_project).execute
+
+      assignment.compatible = res.success?
+      assignment.save!
+    end
+  end
+end
diff --git a/app/models/namespace_project_runtime_assignment.rb b/app/models/namespace_project_runtime_assignment.rb
index d3ac2444..12832568 100644
--- a/app/models/namespace_project_runtime_assignment.rb
+++ b/app/models/namespace_project_runtime_assignment.rb
@@ -9,6 +9,8 @@ class NamespaceProjectRuntimeAssignment < ApplicationRecord
   validate :validate_namespaces, if: :runtime_changed?
   validate :validate_namespaces, if: :namespace_project_changed?
 
+  scope :compatible, -> { where(compatible: true) }
+
   private
 
   def validate_namespaces
diff --git a/app/services/error_code.rb b/app/services/error_code.rb
index 2ef87976..06510c10 100644
--- a/app/services/error_code.rb
+++ b/app/services/error_code.rb
@@ -72,6 +72,10 @@ def self.error_codes
       primary_level_not_found: { description: '', deprecation_reason: 'Outdated concept' },
       secondary_level_not_found: { description: '', deprecation_reason: 'Outdated concept' },
       tertiary_level_exceeds_parameters: { description: '', deprecation_reason: 'Outdated concept' },
+
+      missing_primary_runtime: { description: 'The project is missing a primary runtime' },
+      missing_definition: { description: 'The primary runtime has more definitions than this one' },
+      outdated_definition: { description: 'The primary runtime has a newer definition than this one' },
     }
   end
 end
diff --git a/app/services/namespaces/projects/assign_runtimes_service.rb b/app/services/namespaces/projects/assign_runtimes_service.rb
index a37ec69e..918a424a 100644
--- a/app/services/namespaces/projects/assign_runtimes_service.rb
+++ b/app/services/namespaces/projects/assign_runtimes_service.rb
@@ -32,6 +32,8 @@ def execute
             )
           end
 
+          UpdateRuntimeCompatibilityJob.perform_later({ namespace_project_id: namespace_project.id })
+
           AuditService.audit(
             :project_runtimes_assigned,
             author_id: current_authentication.user.id,
diff --git a/app/services/runtimes/check_runtime_compatibility_service.rb b/app/services/runtimes/check_runtime_compatibility_service.rb
new file mode 100644
index 00000000..1f7c0b85
--- /dev/null
+++ b/app/services/runtimes/check_runtime_compatibility_service.rb
@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+module Runtimes
+  class CheckRuntimeCompatibilityService
+    attr_reader :runtime, :namespace_project
+
+    def initialize(runtime, namespace_project)
+      @runtime = runtime
+      @namespace_project = namespace_project
+    end
+
+    def execute
+      primary_runtime = namespace_project.primary_runtime
+
+      if primary_runtime.nil?
+        return ServiceResponse.error(message: 'No primary runtime given',
+                                     error_code: :missing_primary_runtime)
+      end
+
+      { DataType => :identifier, FlowType => :identifier,
+        RuntimeFunctionDefinition => :runtime_name }.each do |model, identifier_field|
+        res = check_versions(model, identifier_field)
+        return res if res.error?
+      end
+      ServiceResponse.success(message: 'Runtime is compatible', payload: runtime)
+    end
+
+    def check_versions(model, identifier_field = :identifier)
+      to_check_types = model.where(runtime: runtime)
+      primary_types = model.where(runtime: namespace_project.primary_runtime)
+
+      if to_check_types.size < primary_types.size
+        return ServiceResponse.error(message: "#{model} amount dont match",
+                                     error_code: :missing_definition)
+      end
+
+      primary_types.each do |curr_type|
+        to_check = model.find_by(runtime: runtime, identifier_field => curr_type.send(identifier_field))
+        if to_check.nil?
+          return ServiceResponse.error(message: "#{model} is not present in new runtime",
+                                       error_code: :missing_definition)
+        end
+
+        result = compare_version(curr_type.parsed_version, to_check.parsed_version)
+
+        unless result
+          return ServiceResponse.error(message: "#{model} is outdated",
+                                       error_code: :outdated_definition)
+        end
+      end
+      ServiceResponse.success
+    end
+
+    # true: compatible
+    # false: not compatible
+    def compare_version(primary_version, to_check_version)
+      return false if primary_version.segments[0] != to_check_version.segments[0]
+      return false if primary_version.segments[1] > to_check_version.segments[1]
+
+      true
+    end
+  end
+end
diff --git a/app/services/runtimes/data_types/update_service.rb b/app/services/runtimes/data_types/update_service.rb
index 9257fae5..043f8532 100644
--- a/app/services/runtimes/data_types/update_service.rb
+++ b/app/services/runtimes/data_types/update_service.rb
@@ -24,6 +24,8 @@ def execute
             end
           end
 
+          UpdateRuntimeCompatibilityJob.perform_later({ runtime_id: current_runtime.id })
+
           ServiceResponse.success(message: 'Updated data types', payload: data_types)
         end
       end
diff --git a/app/services/runtimes/flow_types/update_service.rb b/app/services/runtimes/flow_types/update_service.rb
index 8f0b6838..34391057 100644
--- a/app/services/runtimes/flow_types/update_service.rb
+++ b/app/services/runtimes/flow_types/update_service.rb
@@ -24,6 +24,8 @@ def execute
             end
           end
 
+          UpdateRuntimeCompatibilityJob.perform_later({ runtime_id: current_runtime.id })
+
           ServiceResponse.success(message: 'Updated data types', payload: flow_types)
         end
       end
diff --git a/app/services/runtimes/runtime_function_definitions/update_service.rb b/app/services/runtimes/runtime_function_definitions/update_service.rb
index 00d8d3f6..47f68d18 100644
--- a/app/services/runtimes/runtime_function_definitions/update_service.rb
+++ b/app/services/runtimes/runtime_function_definitions/update_service.rb
@@ -25,6 +25,8 @@ def execute
             end
           end
 
+          UpdateRuntimeCompatibilityJob.perform_later({ runtime_id: current_runtime.id })
+
           ServiceResponse.success(message: 'Updated runtime function definition', payload: runtime_function_definitions)
         end
       end
diff --git a/config/environments/test.rb b/config/environments/test.rb
index 983be8e7..bffdd608 100644
--- a/config/environments/test.rb
+++ b/config/environments/test.rb
@@ -46,6 +46,9 @@
   # ActionMailer::Base.deliveries array.
   config.action_mailer.delivery_method = :test
 
+  # Use test adapter for ActiveJob to avoid connection leaks from GoodJob
+  config.active_job.queue_adapter = :test
+
   # Print deprecation notices to the stderr.
   config.active_support.deprecation = :stderr
 
diff --git a/db/migrate/20251109141754_add_is_compatible_to_primary_runtime.rb b/db/migrate/20251109141754_add_is_compatible_to_primary_runtime.rb
new file mode 100644
index 00000000..04d79557
--- /dev/null
+++ b/db/migrate/20251109141754_add_is_compatible_to_primary_runtime.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AddIsCompatibleToPrimaryRuntime < Code0::ZeroTrack::Database::Migration[1.0]
+  def change
+    add_column :namespace_project_runtime_assignments, :compatible, :boolean, null: false, default: false
+  end
+end
diff --git a/db/schema_migrations/20251109141754 b/db/schema_migrations/20251109141754
new file mode 100644
index 00000000..1aac43df
--- /dev/null
+++ b/db/schema_migrations/20251109141754
@@ -0,0 +1 @@
+d8a8171eddb13a575d76518ba6092f9f96d3b1e238d04da86104efc117ffbf14
\ No newline at end of file
diff --git a/db/structure.sql b/db/structure.sql
index 70da55b8..bd28c700 100644
--- a/db/structure.sql
+++ b/db/structure.sql
@@ -465,7 +465,8 @@ CREATE TABLE namespace_project_runtime_assignments (
     runtime_id bigint NOT NULL,
     namespace_project_id bigint NOT NULL,
     created_at timestamp with time zone NOT NULL,
-    updated_at timestamp with time zone NOT NULL
+    updated_at timestamp with time zone NOT NULL,
+    compatible boolean DEFAULT false NOT NULL
 );
 
 CREATE SEQUENCE namespace_project_runtime_assignments_id_seq
diff --git a/docs/graphql/enum/errorcodeenum.md b/docs/graphql/enum/errorcodeenum.md
index 6df06179..6f37393f 100644
--- a/docs/graphql/enum/errorcodeenum.md
+++ b/docs/graphql/enum/errorcodeenum.md
@@ -45,9 +45,11 @@ Represents the available error responses
 | `LOADING_IDENTITY_FAILED` | Failed to load user identity from external provider |
 | `MFA_FAILED` | Invalid MFA data provided |
 | `MFA_REQUIRED` | MFA is required |
+| `MISSING_DEFINITION` | The primary runtime has more definitions than this one |
 | `MISSING_IDENTITY_DATA` | This external identity is missing data |
 | `MISSING_PARAMETER` | Not all required parameters are present |
 | `MISSING_PERMISSION` | The user is not permitted to perform this operation |
+| `MISSING_PRIMARY_RUNTIME` | The project is missing a primary runtime |
 | `NAMESPACE_MEMBER_NOT_FOUND` | The namespace member with the given identifier was not found |
 | `NAMESPACE_NOT_FOUND` | The namespace with the given identifier was not found |
 | `NAMESPACE_PROJECT_NOT_FOUND` | The namespace project with the given identifier was not found |
@@ -55,6 +57,7 @@ Represents the available error responses
 | `NO_FREE_LICENSE_SEATS` | There are no free license seats to complete this operation |
 | `NO_PRIMARY_RUNTIME` | The project does not have a primary runtime |
 | `ORGANIZATION_NOT_FOUND` | The organization with the given identifier was not found |
+| `OUTDATED_DEFINITION` | The primary runtime has a newer definition than this one |
 | `PRIMARY_LEVEL_NOT_FOUND` | **Deprecated:** Outdated concept |
 | `PROJECT_NOT_FOUND` | The namespace project with the given identifier was not found |
 | `REGISTRATION_DISABLED` | Self-registration is disabled |
diff --git a/spec/jobs/update_runtime_compatibility_job_spec.rb b/spec/jobs/update_runtime_compatibility_job_spec.rb
new file mode 100644
index 00000000..c23f773d
--- /dev/null
+++ b/spec/jobs/update_runtime_compatibility_job_spec.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe UpdateRuntimeCompatibilityJob do
+  include ActiveJob::TestHelper
+
+  it 'calls the compatibility service for each assignment and updates compatible' do
+    assignment1 = create(:namespace_project_runtime_assignment, compatible: false)
+    assignment2 = create(:namespace_project_runtime_assignment, compatible: false)
+
+    success_res = ServiceResponse.success
+    err_response = ServiceResponse.error(error_code: :outdated_definition, message: 'Runtime is outdated')
+
+    service1 = instance_double(Runtimes::CheckRuntimeCompatibilityService, execute: success_res)
+    service2 = instance_double(Runtimes::CheckRuntimeCompatibilityService, execute: err_response)
+
+    allow(Runtimes::CheckRuntimeCompatibilityService).to receive(:new)
+      .with(assignment1.runtime, assignment1.namespace_project).and_return(service1)
+    allow(Runtimes::CheckRuntimeCompatibilityService).to receive(:new)
+      .with(assignment2.runtime, assignment2.namespace_project).and_return(service2)
+
+    conditions = { id: [assignment1.id, assignment2.id] }
+
+    perform_enqueued_jobs do
+      described_class.perform_later(conditions)
+    end
+
+    expect(assignment1.reload.compatible).to be true
+    expect(assignment2.reload.compatible).to be false
+  end
+end
diff --git a/spec/services/runtimes/check_runtime_compatibility_service_spec.rb b/spec/services/runtimes/check_runtime_compatibility_service_spec.rb
new file mode 100644
index 00000000..85f943cd
--- /dev/null
+++ b/spec/services/runtimes/check_runtime_compatibility_service_spec.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe Runtimes::CheckRuntimeCompatibilityService do
+  subject(:service_response) do
+    described_class.new(runtime, project).execute
+  end
+
+  let(:primary_runtime) { create(:runtime) }
+  let(:runtime) { create(:runtime) }
+  let(:project) { create(:namespace_project, primary_runtime: primary_runtime) }
+
+  context 'when primary runtime is missing' do
+    let(:project) { create(:namespace_project) }
+
+    it 'returns an error with :missing_primary_runtime payload' do
+      expect(service_response).to be_error
+      expect(service_response.payload[:error_code]).to eq(:missing_primary_runtime)
+    end
+  end
+
+  context 'when a model has fewer types on the runtime than on the primary' do
+    before do
+      create(:data_type, runtime: primary_runtime)
+    end
+
+    it 'returns missing_datatypes error' do
+      expect(service_response.error?).to be true
+      expect(service_response.payload[:error_code]).to eq(:missing_definition)
+    end
+  end
+
+  context 'when secondary runtime has outdated definitions' do
+    before do
+      create(:data_type, runtime: primary_runtime, identifier: 'dt1', version: '1.3.0')
+      create(:data_type, runtime: runtime, identifier: 'dt1', version: '1.2.0')
+    end
+
+    it 'returns outdated_data_type error' do
+      expect(service_response.error?).to be true
+      expect(service_response.payload[:error_code]).to eq(:outdated_definition)
+    end
+  end
+
+  context 'when all models are compatible' do
+    before do
+      create(:data_type, runtime: primary_runtime, identifier: 'dt1', version: '1.3.0')
+      create(:data_type, runtime: runtime, identifier: 'dt1', version: '1.3.0')
+      create(:flow_type, runtime: primary_runtime, identifier: 'ft1', version: '2.1.0')
+      create(:flow_type, runtime: runtime, identifier: 'ft1', version: '2.2.0')
+      create(:runtime_function_definition, runtime_name: 'rfd1', runtime: primary_runtime, version: '3.0.0')
+      create(:runtime_function_definition, runtime_name: 'rfd1', runtime: runtime, version: '3.1.0')
+    end
+
+    it 'returns success with the runtime as payload' do
+      expect(service_response).to be_success
+      expect(service_response.payload).to eq(runtime)
+    end
+  end
+end