diff --git a/lib/log_struct/builders/active_job.rb b/lib/log_struct/builders/active_job.rb
index 5691bf8..d7c8fa0 100644
--- a/lib/log_struct/builders/active_job.rb
+++ b/lib/log_struct/builders/active_job.rb
@@ -21,9 +21,12 @@ def self.safe_executions(job)
         job.respond_to?(:executions) ? job.executions : nil
       end
 
+      # Respect log_arguments? setting on job classes.
+      # Arguments are logged by default but can be opted-out per job class.
+      # When logged, sensitive keys are filtered by Formatter.process_values.
       sig { params(job: T.untyped).returns(T.nilable(T::Array[T.untyped])) }
       def self.safe_arguments(job)
-        return nil unless job.class.respond_to?(:log_arguments?)
+        return job.arguments unless job.class.respond_to?(:log_arguments?)
         job.class.log_arguments? ? job.arguments : nil
       end
 
diff --git a/lib/log_struct/config_struct/filters.rb b/lib/log_struct/config_struct/filters.rb
index 09fe14f..56600f4 100644
--- a/lib/log_struct/config_struct/filters.rb
+++ b/lib/log_struct/config_struct/filters.rb
@@ -88,11 +88,32 @@ class Filters < T::Struct
       # Default: false
       prop :mac_addresses, T::Boolean, default: false
 
+      # Default regex pattern for matching sensitive keys.
+      # Matches keys containing: password, token, secret, auth, cred
+      # Also matches specific key patterns: api_key, secret_key, private_key, access_key, encryption_key
+      # Examples: access_token, api_key, auth_header, credentials
+      # Uses start/end of string or underscore/hyphen boundaries to prevent
+      # false positives like "keyboard" or "turkey" (which contain "key" mid-word)
+      # Note: "key" alone is too broad (matches cron_key, primary_key), so we only match
+      # specific sensitive key patterns
+      DEFAULT_SENSITIVE_KEY_PATTERN = T.let(
+        /(^|[_-])(password|token|secret|auth|cred)([_-]|$)|(^|[_-])(api|secret|private|access|encryption)_key([_-]|$)/i,
+        Regexp
+      )
+
       # Additional filter matchers built from Rails filter_parameters entries that aren't simple symbols.
       # Each matcher receives the key (String) and optional value, returning true when the pair should be filtered.
+      # By default, includes a regex matcher for common sensitive key patterns.
       prop :filter_matchers,
         T::Array[FilterMatcher],
-        factory: -> { [] }
+        factory: -> {
+          [
+            FilterMatcher.new(
+              callable: ->(key, _value) { DEFAULT_SENSITIVE_KEY_PATTERN.match?(key) },
+              label: "default_sensitive_pattern"
+            )
+          ]
+        }
     end
   end
 end
diff --git a/lib/log_struct/integrations/active_record.rb b/lib/log_struct/integrations/active_record.rb
index 45eeed0..2e0e03d 100644
--- a/lib/log_struct/integrations/active_record.rb
+++ b/lib/log_struct/integrations/active_record.rb
@@ -281,6 +281,12 @@ def self.looks_sensitive?(value)
         return true if value.match?(/\A[A-Za-z0-9+\/]{20,}={0,2}\z/)  # Base64
         return true if value.match?(/(password|secret|token|key|auth)/i)
 
+        # Filter JWT tokens (header.payload.signature format, starts with "ey")
+        return true if value.match?(/\Aey[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\z/)
+
+        # Filter Bearer tokens
+        return true if value.match?(/\ABearer\s+/i)
+
         false
       end
     end
diff --git a/lib/log_struct/integrations/good_job/log_subscriber.rb b/lib/log_struct/integrations/good_job/log_subscriber.rb
index 5dad56c..e63fa26 100644
--- a/lib/log_struct/integrations/good_job/log_subscriber.rb
+++ b/lib/log_struct/integrations/good_job/log_subscriber.rb
@@ -148,11 +148,21 @@ def build_base_fields(job, payload)
             job_id: job&.job_id,
             job_class: job&.job_class,
             queue_name: job&.queue_name&.to_sym,
-            arguments: job&.arguments,
+            arguments: safe_arguments(job),
             executions: execution&.executions
           )
         end
 
+        # Respect log_arguments? setting on job classes (consistent with ActiveJob behavior).
+        # Arguments are logged by default but can be opted-out per job class.
+        # When logged, sensitive keys are filtered by Formatter.process_values.
+        sig { params(job: T.untyped).returns(T.nilable(T::Array[T.untyped])) }
+        def safe_arguments(job)
+          return nil unless job
+          return job.arguments unless job.class.respond_to?(:log_arguments?)
+          job.class.log_arguments? ? job.arguments : nil
+        end
+
         # Calculate wait time from job creation to execution start
         sig { params(execution: T.untyped).returns(T.nilable(Float)) }
         def calculate_wait_time(execution)
diff --git a/lib/log_struct/shared/merge_additional_data_fields.rb b/lib/log_struct/shared/merge_additional_data_fields.rb
index 186fbf4..e865cef 100644
--- a/lib/log_struct/shared/merge_additional_data_fields.rb
+++ b/lib/log_struct/shared/merge_additional_data_fields.rb
@@ -2,6 +2,7 @@
 # frozen_string_literal: true
 
 require_relative "interfaces/additional_data_field"
+require_relative "../enums/source"
 
 module LogStruct
   module Log
@@ -13,12 +14,24 @@ module MergeAdditionalDataFields
         requires_ancestor { T::Struct }
         requires_ancestor { Interfaces::AdditionalDataField }
 
+        # Reserved keys that cannot be overwritten by additional_data.
+        # These are the core log structure fields that must not be modified.
+        RESERVED_KEYS = T.let(%i[src evt lvl ts].freeze, T::Array[Symbol])
+
         sig { params(hash: T::Hash[Symbol, T.untyped]).void }
         def merge_additional_data_fields(hash)
           ad = additional_data
           return unless ad
           ad.each do |key, value|
-            hash[key.to_sym] = value
+            sym_key = key.to_sym
+            if RESERVED_KEYS.include?(sym_key)
+              LogStruct.handle_exception(
+                ArgumentError.new("additional_data attempted to overwrite reserved key: #{sym_key}"),
+                source: Source::Internal
+              )
+              next
+            end
+            hash[sym_key] = value
           end
         end
       end
diff --git a/rails_test_app/create_app.rb b/rails_test_app/create_app.rb
index e133fd3..482e8cc 100755
--- a/rails_test_app/create_app.rb
+++ b/rails_test_app/create_app.rb
@@ -132,6 +132,9 @@ def rails_supports_skip_kamal?(clean_env)
   "BUNDLER_SETUP" => nil,
   "GEM_HOME" => nil,
   "GEM_PATH" => nil,
+  # Install gems locally to avoid issues with world-writable system gem directories on CI
+  # (Ruby 4.0 bundler rejects reinstalling gems in world-writable directories for security)
+  "BUNDLE_PATH" => File.join(RAILS_APP_DIR, "vendor", "bundle"),
   # Silence noisy warnings from duplicate gems during generator execution
   "RUBYOPT" => "-W0"
 }
diff --git a/scripts/merge_coverage.sh b/scripts/merge_coverage.sh
index ed5626d..8aa9f26 100755
--- a/scripts/merge_coverage.sh
+++ b/scripts/merge_coverage.sh
@@ -1,3 +1,3 @@
 #!/usr/bin/env bash
 
-rake coverage:merge
+bundle exec rake coverage:merge
diff --git a/scripts/rails_tests.sh b/scripts/rails_tests.sh
index 0642fe0..7044b8f 100755
--- a/scripts/rails_tests.sh
+++ b/scripts/rails_tests.sh
@@ -75,6 +75,10 @@ export RUBYOPT="-W0"
 # Set CI=true so LogStruct is enabled for integration tests
 export CI=true
 
+# Install gems locally to avoid issues with world-writable system gem directories on CI
+# (Ruby 4.0 bundler rejects reinstalling gems in world-writable directories for security)
+export BUNDLE_PATH="$TEST_APP_DIR/vendor/bundle"
+
 # Install gems for the test app under the selected Ruby
 bundle install
 
diff --git a/test/log_struct/integrations/active_record_test.rb b/test/log_struct/integrations/active_record_test.rb
index 3278a26..c433b3a 100644
--- a/test/log_struct/integrations/active_record_test.rb
+++ b/test/log_struct/integrations/active_record_test.rb
@@ -293,6 +293,58 @@ class ActiveRecordTest < ActiveSupport::TestCase
         assert_includes T.must(log).bind_params, 123
       end
 
+      test "filters JWT tokens in bind parameters" do
+        LogStruct.config.integrations.sql_log_bind_params = true
+        setup_activerecord_for_test
+
+        # Real-looking JWT token (header.payload.signature format, starts with "ey")
+        # cspell:disable-next-line
+        jwt_token = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c"
+
+        logged_events = []
+        LogStruct.stub(:info, ->(log) { logged_events << log }) do
+          simulate_sql_notification(
+            binds: [jwt_token, "normal_value"],
+            type_casted_binds: [jwt_token, "normal_value"]
+          )
+        end
+
+        assert_equal 1, logged_events.size
+        log = T.let(logged_events.first, T.nilable(LogStruct::Log::SQL))
+
+        assert_not_nil log
+
+        # JWT token should be filtered
+        assert_includes T.must(log).bind_params, "[FILTERED]"
+        # Normal value should pass through
+        assert_includes T.must(log).bind_params, "normal_value"
+      end
+
+      test "filters Bearer tokens in bind parameters" do
+        LogStruct.config.integrations.sql_log_bind_params = true
+        setup_activerecord_for_test
+
+        bearer_token = "Bearer abc123def456"
+
+        logged_events = []
+        LogStruct.stub(:info, ->(log) { logged_events << log }) do
+          simulate_sql_notification(
+            binds: [bearer_token, "safe_value"],
+            type_casted_binds: [bearer_token, "safe_value"]
+          )
+        end
+
+        assert_equal 1, logged_events.size
+        log = T.let(logged_events.first, T.nilable(LogStruct::Log::SQL))
+
+        assert_not_nil log
+
+        # Bearer token should be filtered
+        assert_includes T.must(log).bind_params, "[FILTERED]"
+        # Safe value should pass through
+        assert_includes T.must(log).bind_params, "safe_value"
+      end
+
       test "excludes bind parameters when disabled" do
         LogStruct.config.integrations.sql_log_bind_params = false
         setup_activerecord_for_test
diff --git a/test/log_struct/integrations/good_job/log_subscriber_test.rb b/test/log_struct/integrations/good_job/log_subscriber_test.rb
index 99ece8a..b0b3145 100644
--- a/test/log_struct/integrations/good_job/log_subscriber_test.rb
+++ b/test/log_struct/integrations/good_job/log_subscriber_test.rb
@@ -266,6 +266,67 @@ class LogSubscriberTest < ActiveSupport::TestCase
           assert_nil wait_time
         end
 
+        test "respects log_arguments? when job class opts out" do
+          clear_log_buffer(@log_output)
+
+          # Create a job class that opts out of logging arguments
+          job_class = Class.new do
+            def self.log_arguments?
+              false
+            end
+          end
+          Object.const_set(:NoLogArgsJob, job_class)
+
+          begin
+            log = run_enqueue_with_job_class(:NoLogArgsJob)
+
+            refute log.key?("arguments")
+          ensure
+            Object.send(:remove_const, :NoLogArgsJob)
+          end
+        end
+
+        test "logs arguments by default when job class does not define log_arguments?" do
+          clear_log_buffer(@log_output)
+
+          # Standard job without log_arguments? defined - should log arguments
+          job = create_mock_job("StandardJob", "job_123", "default")
+          event_data = create_test_event({
+            job: job,
+            duration: 0.1
+          })
+
+          @subscriber.enqueue(event_data)
+          ::SemanticLogger.flush
+
+          output = @log_output.string
+          log = JSON.parse(output.lines.first.strip)
+
+          # Arguments should be present by default
+          assert log.key?("arguments")
+          assert_equal ["arg1", "arg2"], log["arguments"]
+        end
+
+        test "logs arguments when job class log_arguments? returns true" do
+          clear_log_buffer(@log_output)
+
+          job_class = Class.new do
+            def self.log_arguments?
+              true
+            end
+          end
+          Object.const_set(:LogArgsJob, job_class)
+
+          begin
+            log = run_enqueue_with_job_class(:LogArgsJob)
+
+            assert log.key?("arguments")
+            assert_equal ["arg1", "arg2"], log["arguments"]
+          ensure
+            Object.send(:remove_const, :LogArgsJob)
+          end
+        end
+
         private
 
         def create_test_event(payload_data, start_time: nil, finish_time: nil)
@@ -293,6 +354,35 @@ def create_mock_job(job_class, job_id, queue_name, extra_attributes = {})
           }.merge(extra_attributes))
         end
 
+        # Create a mock job where job.class returns the actual job class (for testing log_arguments?)
+        def create_mock_job_with_class(klass, job_id, queue_name, extra_attributes = {})
+          mock = Object.new
+          mock.define_singleton_method(:class) { klass }
+          mock.define_singleton_method(:job_class) { klass.name }
+          mock.define_singleton_method(:job_id) { job_id }
+          mock.define_singleton_method(:queue_name) { queue_name }
+          mock.define_singleton_method(:arguments) { ["arg1", "arg2"] }
+          mock.define_singleton_method(:priority) { 0 }
+          mock.define_singleton_method(:scheduled_at) { nil }
+          mock.define_singleton_method(:enqueue_caller_location) { nil }
+          extra_attributes.each do |key, value|
+            mock.define_singleton_method(key) { value }
+          end
+          mock
+        end
+
+        # Run an enqueue event with a job class that has log_arguments? method and return the parsed log
+        def run_enqueue_with_job_class(job_class)
+          # rubocop:disable Sorbet/ConstantsFromStrings
+          klass = Object.const_get(job_class)
+          # rubocop:enable Sorbet/ConstantsFromStrings
+          job = create_mock_job_with_class(klass, "job_123", "default")
+          event_data = create_test_event({job: job, duration: 0.1})
+          @subscriber.enqueue(event_data)
+          ::SemanticLogger.flush
+          JSON.parse(@log_output.string.lines.first.strip)
+        end
+
         def create_mock_execution(attributes = {})
           OpenStruct.new({
             executions: 1,
diff --git a/test/log_struct/integrations/lograge_formatter_test.rb b/test/log_struct/integrations/lograge_formatter_test.rb
index c529ea4..51cce60 100644
--- a/test/log_struct/integrations/lograge_formatter_test.rb
+++ b/test/log_struct/integrations/lograge_formatter_test.rb
@@ -180,6 +180,41 @@ def test_prefers_payload_request_id_over_header
 
         assert_equal "payload-request-id", options[:request_id]
       end
+
+      def test_additional_data_cannot_overwrite_reserved_keys
+        # Reserved keys are: src, evt, lvl, ts
+        data = {
+          method: "GET",
+          path: "/users",
+          status: 200,
+          duration: 12.34,
+          # These should be in additional_data but NOT overwrite the real values
+          src: "attacker",
+          evt: "spoofed",
+          lvl: "fake",
+          ts: "2000-01-01T00:00:00Z"
+        }
+
+        exceptions_reported = []
+        LogStruct.stub(:handle_exception, ->(exc, source:) { exceptions_reported << [exc, source] }) do
+          log = @formatter.call(data)
+          json_hash = log.serialize
+
+          # Reserved keys should retain their real values
+          assert_equal "rails", json_hash[:src]
+          assert_equal "request", json_hash[:evt]
+          assert_equal "info", json_hash[:lvl]
+          refute_equal "2000-01-01T00:00:00Z", json_hash[:ts]
+        end
+
+        # Should have reported 4 exceptions (one for each reserved key attempted)
+        assert_equal 4, exceptions_reported.size
+        exceptions_reported.each do |exc, source|
+          assert_kind_of ArgumentError, exc
+          assert_match(/additional_data attempted to overwrite reserved key/, exc.message)
+          assert_equal LogStruct::Source::Internal, source
+        end
+      end
     end
   end
 end
diff --git a/test/log_struct/param_filters_test.rb b/test/log_struct/param_filters_test.rb
index 323bda6..eef1a74 100644
--- a/test/log_struct/param_filters_test.rb
+++ b/test/log_struct/param_filters_test.rb
@@ -103,5 +103,51 @@ class ParamFiltersTest < ActiveSupport::TestCase
 
       assert_equal Integer, s5[:_class]
     end
+
+    test "default regex filter matcher catches common sensitive key patterns" do
+      # Reset config to use fresh defaults (with default filter_matchers)
+      LogStruct.configuration = LogStruct::Configuration.new
+
+      # Should filter keys containing sensitive patterns with word boundaries
+      assert ParamFilters.should_filter_key?(:access_token)
+      assert ParamFilters.should_filter_key?(:refresh_token)
+      assert ParamFilters.should_filter_key?(:api_key)
+      assert ParamFilters.should_filter_key?(:private_key)
+      assert ParamFilters.should_filter_key?(:secret_key)
+      assert ParamFilters.should_filter_key?(:access_key)
+      assert ParamFilters.should_filter_key?(:encryption_key)
+      assert ParamFilters.should_filter_key?(:client_secret)
+      assert ParamFilters.should_filter_key?(:auth_header)
+      assert ParamFilters.should_filter_key?(:auth_token)
+      assert ParamFilters.should_filter_key?(:credentials)
+      assert ParamFilters.should_filter_key?(:password_hash)
+
+      # Case insensitive
+      assert ParamFilters.should_filter_key?(:ACCESS_TOKEN)
+      assert ParamFilters.should_filter_key?(:Api_Key)
+    end
+
+    test "default regex filter matcher does not match false positives" do
+      # Reset config to use fresh defaults (with default filter_matchers)
+      LogStruct.configuration = LogStruct::Configuration.new
+
+      # Word boundaries should prevent these false positives
+      refute ParamFilters.should_filter_key?(:keyboard)
+      refute ParamFilters.should_filter_key?(:turkey)
+      refute ParamFilters.should_filter_key?(:monkey)
+      refute ParamFilters.should_filter_key?(:hockey)
+      refute ParamFilters.should_filter_key?(:credenza)
+
+      # "key" alone is too broad - these should NOT be filtered
+      refute ParamFilters.should_filter_key?(:cron_key)
+      refute ParamFilters.should_filter_key?(:primary_key)
+      refute ParamFilters.should_filter_key?(:foreign_key)
+      refute ParamFilters.should_filter_key?(:unique_key)
+
+      # Normal fields should not be filtered
+      refute ParamFilters.should_filter_key?(:username)
+      refute ParamFilters.should_filter_key?(:email_address)
+      refute ParamFilters.should_filter_key?(:first_name)
+    end
   end
 end