diff --git a/.buildkite/pipeline.yml b/.buildkite/pipeline.yml
index 0227b5830e..2196eee35b 100644
--- a/.buildkite/pipeline.yml
+++ b/.buildkite/pipeline.yml
@@ -5,7 +5,7 @@ steps:
     env:
       RUBY_VERSION: "{{ matrix.ruby }}"
       TEST_SUITE: "{{ matrix.suite }}"
-      STACK_VERSION: 8.16.3-SNAPSHOT
+      STACK_VERSION: 8.16.5-SNAPSHOT
       TRANSPORT_VERSION: "{{ matrix.transport }}"
       RUBY_SOURCE: "{{ matrix.ruby_source }}"
       QUIET: false
@@ -62,7 +62,7 @@ steps:
       provider: "gcp"
     env:
       RUBY_VERSION: "3.3"
-      STACK_VERSION: 8.16.3-SNAPSHOT
+      STACK_VERSION: 8.16.5-SNAPSHOT
       ES_YAML_TESTS_BRANCH: 8.16
       TRANSPORT_VERSION: "8.3"
       RUBY_SOURCE: "ruby"
diff --git a/.github/workflows/8.16.yml b/.github/workflows/8.16.yml
index d49b453ce4..2c9d61c11e 100644
--- a/.github/workflows/8.16.yml
+++ b/.github/workflows/8.16.yml
@@ -26,7 +26,7 @@ jobs:
         sudo sysctl -w vm.max_map_count=262144
     - uses: elastic/elastic-github-actions/elasticsearch@master
       with:
-        stack-version: 8.16.3-SNAPSHOT
+        stack-version: 8.16.5-SNAPSHOT
         security-enabled: false
     - uses: ruby/setup-ruby@v1
       with:
@@ -40,4 +40,4 @@ jobs:
     - name: elasticsearch
       run: cd elasticsearch && bundle exec rake test:all
     - name: elasticsearch-api
-      run: rake es:download_artifacts[8.16.3-SNAPSHOT] && cd elasticsearch-api && bundle exec rake test:spec test:platinum:unit
+      run: rake es:download_artifacts[8.16.5-SNAPSHOT] && cd elasticsearch-api && bundle exec rake test:spec test:platinum:unit
diff --git a/.github/workflows/otel.yml b/.github/workflows/otel.yml
index 292d2bcfc3..697f8dd086 100644
--- a/.github/workflows/otel.yml
+++ b/.github/workflows/otel.yml
@@ -28,7 +28,7 @@ jobs:
           sudo sysctl -w vm.max_map_count=262144
       - uses: elastic/elastic-github-actions/elasticsearch@master
         with:
-          stack-version: 8.16.3-SNAPSHOT
+          stack-version: 8.16.5-SNAPSHOT
           security-enabled: false
       - uses: ruby/setup-ruby@v1
         with:
@@ -42,4 +42,4 @@ jobs:
       - name: elasticsearch
         run: cd elasticsearch && bundle exec rake test:all
       - name: elasticsearch-api
-        run: rake es:download_artifacts[8.16.3-SNAPSHOT] && cd elasticsearch-api && bundle exec rake test:spec test:platinum:unit
+        run: rake es:download_artifacts[8.16.5-SNAPSHOT] && cd elasticsearch-api && bundle exec rake test:spec test:platinum:unit
diff --git a/elasticsearch-api/elasticsearch-api.gemspec b/elasticsearch-api/elasticsearch-api.gemspec
index a458ed60d1..f2149ebda2 100644
--- a/elasticsearch-api/elasticsearch-api.gemspec
+++ b/elasticsearch-api/elasticsearch-api.gemspec
@@ -59,15 +59,10 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'yard'
 
   # Gems for testing integrations
-  s.add_development_dependency 'jsonify'
+  s.add_development_dependency 'activesupport'
   s.add_development_dependency 'hashie'
-  # Temporary support for Ruby 2.6, since it's EOL March 2022:
-  if RUBY_VERSION < '2.7.0'
-    s.add_development_dependency 'jbuilder', '< 7.0.0'
-  else
-    s.add_development_dependency 'activesupport'
-    s.add_development_dependency 'jbuilder'
-  end
+  s.add_development_dependency 'jbuilder'
+  s.add_development_dependency 'jsonify'
 
   s.add_development_dependency 'cane'
   s.add_development_dependency 'escape_utils' unless defined? JRUBY_VERSION
diff --git a/elasticsearch-api/spec/spec_helper.rb b/elasticsearch-api/spec/spec_helper.rb
index fe0099ed41..b1d56ee023 100644
--- a/elasticsearch-api/spec/spec_helper.rb
+++ b/elasticsearch-api/spec/spec_helper.rb
@@ -25,15 +25,16 @@
   require 'debug'
 end
 require 'yaml'
-require 'active_support/isolated_execution_state' unless RUBY_VERSION < '2.7.0'
+# Require logger before jbuilder to avoid concurrent-ruby error uninitialized constant
+# ActiveSupport::LoggerThreadSafeLevel::Logger. Dependencies are fun.
+require 'logger'
 require 'jbuilder'
 require 'jsonify'
 require 'elasticsearch'
 require 'elasticsearch-api'
 require 'openssl'
-require 'logger'
 
-tracer = ::Logger.new(STDERR)
+tracer = ::Logger.new($stderr)
 tracer.formatter = lambda { |s, d, p, m| "#{m.gsub(/^.*$/) { |n| '   ' + n } }\n" }
 
 module HelperModule