diff --git a/CHANGELOG.md b/CHANGELOG.md
index a4966c4..6db46e9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,14 @@ All notable changes to this project will be documented in this file.
 ### Added
 - Support for `truffleruby`;
 
+## [0.31.0] - 2026-06-24
+### Changed
+- Performance: nested / dot-notated reads (`config['a.b.c.d.e.f']`, `config.dig(...)`)
+  are now memoized inside each config instance instead of re-splitting and re-digging
+  the key on every access. The cache is dropped on any mutation and the invalidation
+  cascades up through all parent config instances ("matryoshka" cache invalidation),
+  so nested configs (which are separate instances) never serve stale values.
+
 ## [0.30.0] - 2024-12-14
 ### Changed
 - Updated development dependencies;
diff --git a/Gemfile.lock b/Gemfile.lock
index 7645085..4515809 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    qonfig (0.30.0)
+    qonfig (0.31.0)
       base64 (>= 0.2)
 
 GEM
diff --git a/gemfiles/with_external_deps.gemfile.lock b/gemfiles/with_external_deps.gemfile.lock
index 20e7dab..a363440 100644
--- a/gemfiles/with_external_deps.gemfile.lock
+++ b/gemfiles/with_external_deps.gemfile.lock
@@ -1,7 +1,7 @@
 PATH
   remote: ..
   specs:
-    qonfig (0.30.0)
+    qonfig (0.31.0)
       base64 (>= 0.2)
 
 GEM
diff --git a/gemfiles/without_external_deps.gemfile.lock b/gemfiles/without_external_deps.gemfile.lock
index 8c23a05..f7b3e1e 100644
--- a/gemfiles/without_external_deps.gemfile.lock
+++ b/gemfiles/without_external_deps.gemfile.lock
@@ -1,7 +1,7 @@
 PATH
   remote: ..
   specs:
-    qonfig (0.30.0)
+    qonfig (0.31.0)
       base64 (>= 0.2)
 
 GEM
diff --git a/lib/qonfig/commands/definition/add_nested_option.rb b/lib/qonfig/commands/definition/add_nested_option.rb
index b1b55bd..ef4bc4a 100644
--- a/lib/qonfig/commands/definition/add_nested_option.rb
+++ b/lib/qonfig/commands/definition/add_nested_option.rb
@@ -41,10 +41,14 @@ def initialize(key, nested_definitions)
   #
   # @api private
   # @since 0.1.0
+  # @version 0.31.0
   def call(data_set, settings)
     nested_settings = nested_data_set_klass.new.settings
 
-    nested_settings.__mutation_callbacks__.add(settings.__mutation_callbacks__)
+    # NOTE:
+    #   The nested instance is wired into the host's mutation-callback chain by
+    #   Qonfig::Settings#__define_setting__ itself (see __store_setting_value__),
+    #   so every nested-settings entry point shares one wiring path.
     settings.__define_setting__(key, nested_settings)
   end
 end
diff --git a/lib/qonfig/commands/definition/re_define_option.rb b/lib/qonfig/commands/definition/re_define_option.rb
index 7e26333..552ded0 100644
--- a/lib/qonfig/commands/definition/re_define_option.rb
+++ b/lib/qonfig/commands/definition/re_define_option.rb
@@ -48,10 +48,14 @@ def initialize(key, value, nested_definitions)
   #
   # @api private
   # @since 0.20.0
+  # @version 0.31.0
   def call(data_set, settings)
     if nested_data_set_klass
       nested_settings = nested_data_set_klass.new.settings
-      nested_settings.__mutation_callbacks__.add(settings.__mutation_callbacks__)
+      # NOTE:
+      #   The nested instance is wired into the host's mutation-callback chain by
+      #   Qonfig::Settings#__define_setting__ itself (see __store_setting_value__),
+      #   so every nested-settings entry point shares one wiring path.
       settings.__define_setting__(key, nested_settings, with_redefinition: true)
     else
       settings.__define_setting__(key, value, with_redefinition: true)
diff --git a/lib/qonfig/settings.rb b/lib/qonfig/settings.rb
index 3a57762..2e94602 100644
--- a/lib/qonfig/settings.rb
+++ b/lib/qonfig/settings.rb
@@ -48,10 +48,24 @@ class Qonfig::Settings # NOTE: Layout/ClassStructure is disabled only for CORE_M
 
   # @api private
   # @since 0.1.0
+  # @version 0.31.0
   def initialize(__mutation_callbacks__)
     @__options__ = {}
     @__lock__ = Lock.new
     @__mutation_callbacks__ = __mutation_callbacks__
+    @__deep_access_cache__ = {}
+
+    # NOTE:
+    #   Register a cache invalidator inside our own mutation callbacks.
+    #   Nested settings add their parent's callbacks object to their own callbacks
+    #   (see #__store_setting_value__), so a mutation of any nested config propagates
+    #   upwards through the chain and drops the cached digging results on EACH config
+    #   instance along the way ("matryoshka" cache invalidation).
+    #
+    #   It is prepended so that it runs BEFORE the validation callback — full
+    #   data-set validators read setting values back through #__dig__, so the
+    #   cache must already be dropped by the time they run.
+    @__mutation_callbacks__.prepend(method(:__invalidate_deep_access_cache__))
   end
 
   # @param block [Proc]
@@ -93,7 +107,7 @@ def __deep_each_setting__(initial_setting_key = nil, yield_all: false, &block)
   #
   # @api private
   # @since 0.1.0
-  # @version 0.20.0
+  # @version 0.31.0
   def __define_setting__(key, value, with_redefinition: false) # rubocop:disable Metrics/AbcSize
     __lock__.thread_safe_definition do
       key = __indifferently_accessable_option_key__(key)
@@ -102,11 +116,11 @@ def __define_setting__(key, value, with_redefinition: false) # rubocop:disable M
 
       case
       when with_redefinition || !__options__.key?(key)
-        __options__[key] = value
+        __store_setting_value__(key, value)
       when __is_a_setting__(__options__[key]) && __is_a_setting__(value)
         __options__[key].__append_settings__(value)
       else
-        __options__[key] = value
+        __store_setting_value__(key, value)
       end
 
       __define_option_reader__(key)
@@ -175,16 +189,21 @@ def __apply_values__(settings_map)
   #
   # @api private
   # @since 0.2.0
+  # @version 0.31.0
   def __dig__(*keys)
     __lock__.thread_safe_access do
-      begin
-        __deep_access__(*keys)
-      rescue Qonfig::UnknownSettingError
-        if keys.size == 1
-          __deep_access__(*__parse_dot_notated_key__(keys.first))
-        else
-          raise
-        end
+      # NOTE:
+      #   Resolving a dot-notated/nested key (config['a.b.c.d']) is expensive:
+      #   it splits and re-joins string fragments and digs through every nested
+      #   config instance on each access. We memoize the resolved value per key
+      #   set; the cache is dropped on any mutation (see __invalidate...).
+      cache = @__deep_access_cache__
+      cache_key = __deep_access_cache_key__(keys)
+
+      if cache.key?(cache_key)
+        cache[cache_key]
+      else
+        __resolve_deep_access__(*keys).tap { |value| cache[cache_key] = value }
       end
     end
   end
@@ -575,6 +594,75 @@ def __set_value__(key, value)
     __invoke_mutation_callbacks__
   end
 
+  # @param key [String]
+  # @param value [Object]
+  # @return [void]
+  #
+  # @api private
+  # @since 0.31.0
+  def __store_setting_value__(key, value)
+    __options__[key] = value
+
+    # NOTE:
+    #   A nested settings instance can arrive here "foreign" — built under another
+    #   data set and merged into us by reference (compose / load_from_* / expose_* /
+    #   option re-definition). Its mutation callbacks would then still point only at
+    #   the discarded foreign parent, so a mutation of the nested config would never
+    #   invalidate OUR deep-access cache (=> stale reads). Wire the nested instance
+    #   into our callback chain on assignment so invalidation always cascades upwards
+    #   ("matryoshka"), regardless of how the nested settings instance got here.
+    value.__mutation_callbacks__.add(__mutation_callbacks__) if __is_a_setting__(value)
+  end
+
+  # @param keys [Array<String, Symbol>]
+  # @return [Object]
+  #
+  # @raise [Qonfig::UnknownSettingError]
+  #
+  # @api private
+  # @since 0.31.0
+  def __resolve_deep_access__(*keys)
+    __deep_access__(*keys)
+  rescue Qonfig::UnknownSettingError
+    if keys.size == 1
+      __deep_access__(*__parse_dot_notated_key__(keys.first))
+    else
+      raise
+    end
+  end
+
+  # @param keys [Array<String, Symbol>]
+  # @return [String, Array<String>]
+  #
+  # @api private
+  # @since 0.31.0
+  def __deep_access_cache_key__(keys)
+    # NOTE:
+    #   Stringify keys so that symbol/string variants share a single cache slot
+    #   (indifferent access), while preserving key boundaries — ['a.b', 'c'] and
+    #   ['a', 'b', 'c'] resolve differently and must not collide. The single-key
+    #   case (the dominant config['a.b.c'] form) avoids an extra array allocation.
+    (keys.size == 1) ? keys.first.to_s : keys.map(&:to_s)
+  end
+
+  # @return [void]
+  #
+  # @api private
+  # @since 0.31.0
+  def __invalidate_deep_access_cache__
+    # NOTE:
+    #   Reassign (instead of #clear) so concurrent readers never observe a
+    #   half-cleared hash — invalidation can propagate upwards from a nested
+    #   mutation WITHOUT holding our access lock.
+    #
+    #   The reassignment must be UNCONDITIONAL. A `unless empty?` guard would skip
+    #   the swap during the window where a concurrent reader has already resolved a
+    #   now-stale value but has not yet written it into the (still-empty) cache —
+    #   the stale write would then survive and be served forever. Rebinding the ivar
+    #   to a fresh hash makes such a late write land in an orphaned hash instead.
+    @__deep_access_cache__ = {}
+  end
+
   # @param keys [Array<Symbol, String>]
   # @return [Object]
   #
diff --git a/lib/qonfig/settings/callbacks.rb b/lib/qonfig/settings/callbacks.rb
index 7ea30f0..4a20cb8 100644
--- a/lib/qonfig/settings/callbacks.rb
+++ b/lib/qonfig/settings/callbacks.rb
@@ -35,6 +35,15 @@ def add(callback)
     thread_safe { callbacks << callback }
   end
 
+  # @param callback [Proc, Qonfig::Settings::Callbacks, #call]
+  # @return [void]
+  #
+  # @api private
+  # @since 0.31.0
+  def prepend(callback)
+    thread_safe { callbacks.unshift(callback) }
+  end
+
   private
 
   # @return [Array<Proc>]
diff --git a/lib/qonfig/version.rb b/lib/qonfig/version.rb
index c1068bc..91f0af1 100644
--- a/lib/qonfig/version.rb
+++ b/lib/qonfig/version.rb
@@ -5,5 +5,5 @@ module Qonfig
   #
   # @api public
   # @since 0.1.0
-  VERSION = '0.30.0'
+  VERSION = '0.31.0'
 end
diff --git a/spec/features/nested_access_caching_spec.rb b/spec/features/nested_access_caching_spec.rb
new file mode 100644
index 0000000..e4630f3
--- /dev/null
+++ b/spec/features/nested_access_caching_spec.rb
@@ -0,0 +1,134 @@
+# frozen_string_literal: true
+
+describe 'Nested access caching (with matryoshka cache invalidation)' do
+  let(:config) do
+    Qonfig::DataSet.build do
+      setting :a do
+        setting :b do
+          setting :c do
+            setting :d, 1
+          end
+        end
+      end
+
+      setting :flat, 'value'
+    end
+  end
+
+  specify 'repeated dot-notated / nested reads return the same (memoized) result' do
+    expect(config['a.b.c.d']).to eq(1)
+    expect(config['a.b.c.d']).to eq(1)
+
+    nested = config['a.b.c']
+    expect(nested).to be_a(Qonfig::Settings)
+    # the very same nested settings instance is returned from the cache
+    expect(config['a.b.c']).to equal(nested)
+    expect(config.dig(:a, :b, :c)).to equal(nested)
+  end
+
+  specify 'symbol and string key variants share the cache (indifferent access)' do
+    expect(config[:a][:b][:c][:d]).to eq(1)
+    expect(config['a.b.c.d']).to eq(1)
+    expect(config.dig('a', :b, 'c', :d)).to eq(1)
+  end
+
+  specify 'assigning a value invalidates the cache' do
+    expect(config['a.b.c.d']).to eq(1)
+
+    config['a.b.c.d'] = 2
+    expect(config['a.b.c.d']).to eq(2)
+  end
+
+  specify 'mutating a nested config instance invalidates every parent cache (matryoshka)' do
+    # warm up caches on every level
+    expect(config['a.b.c.d']).to eq(1)
+    expect(config['a.b.c']['d']).to eq(1)
+
+    # mutate through a directly-grabbed nested instance
+    nested = config['a.b.c']
+    nested['d'] = 99
+
+    # the mutation must be visible from the root through the (now stale) cache
+    expect(config['a.b.c.d']).to eq(99)
+    expect(config['a.b']['c.d']).to eq(99)
+    expect(nested['d']).to eq(99)
+  end
+
+  specify 'a flat value mutation invalidates the cache' do
+    expect(config['flat']).to eq('value')
+    config['flat'] = 'changed'
+    expect(config['flat']).to eq('changed')
+  end
+
+  specify '#clear! invalidates the cache' do
+    expect(config['a.b.c.d']).to eq(1)
+    config.clear!
+    expect(config['a.b.c.d']).to be_nil
+  end
+
+  specify 'full data-set validators observe fresh values after mutation (no stale cache)' do
+    validated_config = Class.new(Qonfig::DataSet) do
+      setting :nested do
+        setting :flag, :yes
+      end
+
+      validate { settings.nested.flag.is_a?(Symbol) }
+    end
+
+    instance = validated_config.new
+    # warm the cache through the validator-read path
+    expect(instance.settings.nested.flag).to eq(:yes)
+
+    expect { instance.settings.nested.flag = 123 }.to raise_error(Qonfig::ValidationError)
+  end
+
+  specify 'composed nested settings invalidate the host cache on mutation' do
+    shared = Class.new(Qonfig::DataSet) do
+      setting :s do
+        setting :v, 1
+      end
+    end
+
+    host = Qonfig::DataSet.build { compose shared }
+
+    expect(host['s.v']).to eq(1) # warm up the cache through the host
+    host['s.v'] = 88
+    # the nested instance was merged in "by reference"; mutating it must still
+    # cascade invalidation up to the host (otherwise the host serves a stale 1)
+    expect(host['s.v']).to eq(88)
+  end
+
+  specify 're-defined nested settings invalidate the cache on mutation' do
+    redefined_config = Class.new(Qonfig::DataSet) do
+      setting :s do
+        setting :v, 1
+      end
+
+      re_setting :s do
+        setting :v, 10
+      end
+    end
+
+    instance = redefined_config.new
+
+    expect(instance['s.v']).to eq(10) # warm up the cache
+    instance['s.v'] = 77
+    expect(instance['s.v']).to eq(77)
+  end
+
+  specify 'cache invalidation always swaps in a fresh hash, even when already empty' do
+    # Guards the lock-free invalidation contract: invalidation may propagate up
+    # from a nested mutation without holding our access lock, so the swap must be
+    # unconditional. A `unless empty?` guard would let a concurrent reader that has
+    # resolved a stale value (but not yet written it) persist that value forever.
+    settings = config.settings
+    empty_cache = settings.instance_variable_get(:@__deep_access_cache__)
+    expect(empty_cache).to be_empty
+
+    settings.send(:__invalidate_deep_access_cache__)
+
+    swapped_cache = settings.instance_variable_get(:@__deep_access_cache__)
+    expect(swapped_cache).to be_empty
+    expect(swapped_cache).not_to equal(empty_cache)
+  end
+end