diff --git a/temporalio/lib/temporalio/activity/context.rb b/temporalio/lib/temporalio/activity/context.rb
index 9d51769a..edaef5e3 100644
--- a/temporalio/lib/temporalio/activity/context.rb
+++ b/temporalio/lib/temporalio/activity/context.rb
@@ -48,6 +48,12 @@ def info
         raise NotImplementedError
       end
 
+      # @return [Object, nil] Activity class instance. This should always be present except for advanced cases where the
+      #   definition was manually created without any instance getter/creator.
+      def instance
+        raise NotImplementedError
+      end
+
       # Record a heartbeat on the activity.
       #
       # Heartbeats should be used for all non-immediately-returning, non-local activities and they are required to
diff --git a/temporalio/lib/temporalio/activity/definition.rb b/temporalio/lib/temporalio/activity/definition.rb
index 58d8641a..7e06a585 100644
--- a/temporalio/lib/temporalio/activity/definition.rb
+++ b/temporalio/lib/temporalio/activity/definition.rb
@@ -105,7 +105,10 @@ class Info
         # @return [String, Symbol, nil] Name of the activity, or nil if the activity is dynamic.
         attr_reader :name
 
-        # @return [Proc] Proc for the activity.
+        # @return [Object, Proc, nil] The pre-created instance or the proc to create/return it.
+        attr_reader :instance
+
+        # @return [Proc] Proc for the activity. Should use {Context#instance} to access the instance.
         attr_reader :proc
 
         # @return [Symbol] Name of the executor. Default is `:default`.
@@ -134,18 +137,20 @@ def self.from_activity(activity)
             details = activity._activity_definition_details
             new(
               name: details[:activity_name],
+              instance: proc { activity.new },
               executor: details[:activity_executor],
               cancel_raise: details[:activity_cancel_raise],
               raw_args: details[:activity_raw_args]
-            ) { |*args| activity.new.execute(*args) } # Instantiate and call
+            ) { |*args| Context.current.instance&.execute(*args) }
           when Definition
             details = activity.class._activity_definition_details
             new(
               name: details[:activity_name],
+              instance: activity,
               executor: details[:activity_executor],
               cancel_raise: details[:activity_cancel_raise],
               raw_args: details[:activity_raw_args]
-            ) { |*args| activity.execute(*args) } # Just and call
+            ) { |*args| Context.current.instance&.execute(*args) }
           when Info
             activity
           else
@@ -156,12 +161,21 @@ def self.from_activity(activity)
         # Manually create activity definition info. Most users will use an instance/class of {Definition}.
         #
         # @param name [String, Symbol, nil] Name of the activity or nil for dynamic activity.
+        # @param instance [Object, Proc, nil] The pre-created instance or the proc to create/return it.
         # @param executor [Symbol] Name of the executor.
         # @param cancel_raise [Boolean] Whether to raise in thread/fiber on cancellation.
         # @param raw_args [Boolean] Whether to use {Converters::RawValue}s as arguments.
         # @yield Use this block as the activity.
-        def initialize(name:, executor: :default, cancel_raise: true, raw_args: false, &block)
+        def initialize(
+          name:,
+          instance: nil,
+          executor: :default,
+          cancel_raise: true,
+          raw_args: false,
+          &block
+        )
           @name = name
+          @instance = instance
           raise ArgumentError, 'Must give block' unless block_given?
 
           @proc = block
diff --git a/temporalio/lib/temporalio/internal/worker/activity_worker.rb b/temporalio/lib/temporalio/internal/worker/activity_worker.rb
index 46cd0f1f..595a63e6 100644
--- a/temporalio/lib/temporalio/internal/worker/activity_worker.rb
+++ b/temporalio/lib/temporalio/internal/worker/activity_worker.rb
@@ -210,7 +210,7 @@ def execute_activity(task_token, defn, start)
           )
           Activity::Context._current_executor&.set_activity_context(defn, activity)
           set_running_activity(task_token, activity)
-          run_activity(activity, input)
+          run_activity(defn, activity, input)
         rescue Exception => e # rubocop:disable Lint/RescueException We are intending to catch everything here
           @scoped_logger.warn("Failed starting or sending completion for activity #{start.activity_type}")
           @scoped_logger.warn(e)
@@ -236,8 +236,11 @@ def execute_activity(task_token, defn, start)
           remove_running_activity(task_token)
         end
 
-        def run_activity(activity, input)
+        def run_activity(defn, activity, input)
           result = begin
+            # Create the instance. We choose to do this before interceptors so that it is available in the interceptor.
+            activity.instance = defn.instance.is_a?(Proc) ? defn.instance.call : defn.instance # steep:ignore
+
             # Build impl with interceptors
             # @type var impl: Temporalio::Worker::Interceptor::Activity::Inbound
             impl = InboundImplementation.new(self)
@@ -293,7 +296,7 @@ def run_activity(activity, input)
 
         class RunningActivity < Activity::Context
           attr_reader :info, :cancellation, :worker_shutdown_cancellation, :payload_converter, :logger
-          attr_accessor :_outbound_impl, :_server_requested_cancel
+          attr_accessor :instance, :_outbound_impl, :_server_requested_cancel
 
           def initialize( # rubocop:disable Lint/MissingSuper
             info:,
diff --git a/temporalio/lib/temporalio/internal/worker/workflow_instance/context.rb b/temporalio/lib/temporalio/internal/worker/workflow_instance/context.rb
index 6736bd4f..eb094970 100644
--- a/temporalio/lib/temporalio/internal/worker/workflow_instance/context.rb
+++ b/temporalio/lib/temporalio/internal/worker/workflow_instance/context.rb
@@ -122,6 +122,10 @@ def info
             @instance.info
           end
 
+          def instance
+            @instance.instance
+          end
+
           def initialize_continue_as_new_error(error)
             @outbound.initialize_continue_as_new_error(
               Temporalio::Worker::Interceptor::Workflow::InitializeContinueAsNewErrorInput.new(error:)
diff --git a/temporalio/lib/temporalio/testing/activity_environment.rb b/temporalio/lib/temporalio/testing/activity_environment.rb
index 68fc2c72..6d504ac3 100644
--- a/temporalio/lib/temporalio/testing/activity_environment.rb
+++ b/temporalio/lib/temporalio/testing/activity_environment.rb
@@ -80,6 +80,8 @@ def run(activity, *args)
           Activity::Context._current_executor = executor
           executor.set_activity_context(defn, Context.new(
                                                 info: @info.dup,
+                                                instance:
+                                                  defn.instance.is_a?(Proc) ? defn.instance.call : defn.instance,
                                                 on_heartbeat: @on_heartbeat,
                                                 cancellation: @cancellation,
                                                 worker_shutdown_cancellation: @worker_shutdown_cancellation,
@@ -102,17 +104,19 @@ def run(activity, *args)
 
       # @!visibility private
       class Context < Activity::Context
-        attr_reader :info, :cancellation, :worker_shutdown_cancellation, :payload_converter, :logger
+        attr_reader :info, :instance, :cancellation, :worker_shutdown_cancellation, :payload_converter, :logger
 
         def initialize( # rubocop:disable Lint/MissingSuper
-          info: ActivityEnvironment.default_info,
-          on_heartbeat: nil,
-          cancellation: Cancellation.new,
-          worker_shutdown_cancellation: Cancellation.new,
-          payload_converter: Converters::PayloadConverter.default,
-          logger: Logger.new(nil)
+          info:,
+          instance:,
+          on_heartbeat:,
+          cancellation:,
+          worker_shutdown_cancellation:,
+          payload_converter:,
+          logger:
         )
           @info = info
+          @instance = instance
           @on_heartbeat = on_heartbeat
           @cancellation = cancellation
           @worker_shutdown_cancellation = worker_shutdown_cancellation
diff --git a/temporalio/lib/temporalio/workflow.rb b/temporalio/lib/temporalio/workflow.rb
index 2b7e9d6f..c13da19c 100644
--- a/temporalio/lib/temporalio/workflow.rb
+++ b/temporalio/lib/temporalio/workflow.rb
@@ -220,6 +220,12 @@ def self.info
       _current.info
     end
 
+    # @return [Definition, nil] Workflow class instance. This should always be present except in
+    #   {Worker::Interceptor::Workflow::Inbound.init} where it will be nil.
+    def self.instance
+      _current.instance
+    end
+
     # @return [Logger] Logger for the workflow. This is a scoped logger that automatically appends workflow details to
     #   every log and takes care not to log during replay.
     def self.logger
diff --git a/temporalio/sig/temporalio/activity/context.rbs b/temporalio/sig/temporalio/activity/context.rbs
index 5aec9089..930522b4 100644
--- a/temporalio/sig/temporalio/activity/context.rbs
+++ b/temporalio/sig/temporalio/activity/context.rbs
@@ -9,6 +9,7 @@ module Temporalio
       def self._current_executor=: (Worker::ActivityExecutor? executor) -> void
 
       def info: -> Info
+      def instance: -> Definition?
       def heartbeat: (*Object? details) -> void
       def cancellation: -> Cancellation
       def worker_shutdown_cancellation: -> Cancellation
diff --git a/temporalio/sig/temporalio/activity/definition.rbs b/temporalio/sig/temporalio/activity/definition.rbs
index b838fb7b..9b46d29e 100644
--- a/temporalio/sig/temporalio/activity/definition.rbs
+++ b/temporalio/sig/temporalio/activity/definition.rbs
@@ -18,6 +18,7 @@ module Temporalio
 
       class Info
         attr_reader name: String | Symbol | nil
+        attr_reader instance: Object | Proc | nil
         attr_reader proc: Proc
         attr_reader executor: Symbol
         attr_reader cancel_raise: bool
@@ -27,6 +28,7 @@ module Temporalio
 
         def initialize: (
           name: String | Symbol | nil,
+          ?instance: Object | Proc | nil,
           ?executor: Symbol,
           ?cancel_raise: bool,
           ?raw_args: bool
diff --git a/temporalio/sig/temporalio/internal/worker/activity_worker.rbs b/temporalio/sig/temporalio/internal/worker/activity_worker.rbs
index af6364e2..651f3caf 100644
--- a/temporalio/sig/temporalio/internal/worker/activity_worker.rbs
+++ b/temporalio/sig/temporalio/internal/worker/activity_worker.rbs
@@ -21,11 +21,13 @@ module Temporalio
 
         def execute_activity: (String task_token, Activity::Definition::Info defn, untyped start) -> void
         def run_activity: (
+          Activity::Definition::Info defn,
           RunningActivity activity,
           Temporalio::Worker::Interceptor::Activity::ExecuteInput input
         ) -> void
 
         class RunningActivity < Activity::Context
+          attr_accessor instance: Activity::Definition?
           attr_accessor _outbound_impl: Temporalio::Worker::Interceptor::Activity::Outbound?
           attr_accessor _server_requested_cancel: bool
 
diff --git a/temporalio/sig/temporalio/internal/worker/workflow_instance.rbs b/temporalio/sig/temporalio/internal/worker/workflow_instance.rbs
index f4504ad0..19716d40 100644
--- a/temporalio/sig/temporalio/internal/worker/workflow_instance.rbs
+++ b/temporalio/sig/temporalio/internal/worker/workflow_instance.rbs
@@ -40,7 +40,7 @@ module Temporalio
 
         def add_command: (untyped command) -> void
 
-        def instance: -> Object
+        def instance: -> Temporalio::Workflow::Definition
 
         def search_attributes: -> SearchAttributes
 
@@ -58,7 +58,7 @@ module Temporalio
 
         def activate_internal: (untyped activation) -> untyped
 
-        def create_instance: -> Object
+        def create_instance: -> Temporalio::Workflow::Definition
 
         def apply: (untyped job) -> void
 
diff --git a/temporalio/sig/temporalio/internal/worker/workflow_instance/context.rbs b/temporalio/sig/temporalio/internal/worker/workflow_instance/context.rbs
index 0dbf5eae..552fab8d 100644
--- a/temporalio/sig/temporalio/internal/worker/workflow_instance/context.rbs
+++ b/temporalio/sig/temporalio/internal/worker/workflow_instance/context.rbs
@@ -53,6 +53,8 @@ module Temporalio
 
           def info: -> Workflow::Info
 
+          def instance: -> Temporalio::Workflow::Definition?
+
           def initialize_continue_as_new_error: (Workflow::ContinueAsNewError error) -> void
 
           def logger: -> ReplaySafeLogger
diff --git a/temporalio/sig/temporalio/workflow.rbs b/temporalio/sig/temporalio/workflow.rbs
index 9a55ff72..2fded9bd 100644
--- a/temporalio/sig/temporalio/workflow.rbs
+++ b/temporalio/sig/temporalio/workflow.rbs
@@ -64,6 +64,8 @@ module Temporalio
 
     def self.info: -> Info
 
+    def self.instance: -> Definition?
+
     def self.logger: -> ScopedLogger
 
     def self.memo: -> Hash[String, Object?]
diff --git a/temporalio/test/worker_activity_test.rb b/temporalio/test/worker_activity_test.rb
index 5ed29788..8c870066 100644
--- a/temporalio/test/worker_activity_test.rb
+++ b/temporalio/test/worker_activity_test.rb
@@ -857,6 +857,50 @@ def test_dynamic_activity_raw_args
                  execute_activity(DynamicActivityRawArgs, 'arg1', nil, 123, override_name: 'does-not-exist')
   end
 
+  class ContextInstanceInterceptor
+    include Temporalio::Worker::Interceptor::Activity
+
+    def intercept_activity(next_interceptor)
+      Inbound.new(next_interceptor)
+    end
+
+    class Inbound < Temporalio::Worker::Interceptor::Activity::Inbound
+      def init(outbound)
+        Temporalio::Activity::Context.current.instance.events&.<< 'interceptor-init' # steep:ignore
+        super
+      end
+
+      def execute(input)
+        Temporalio::Activity::Context.current.instance.events&.<< 'interceptor-execute' # steep:ignore
+        super
+      end
+    end
+  end
+
+  class ContextInstanceActivity < Temporalio::Activity::Definition
+    def events
+      @events ||= []
+    end
+
+    def execute
+      events << 'execute' # steep:ignore
+    end
+  end
+
+  def test_context_instance
+    # Instance-per-attempt (twice)
+    assert_equal %w[interceptor-init interceptor-execute execute],
+                 execute_activity(ContextInstanceActivity, interceptors: [ContextInstanceInterceptor.new])
+    assert_equal %w[interceptor-init interceptor-execute execute],
+                 execute_activity(ContextInstanceActivity, interceptors: [ContextInstanceInterceptor.new])
+    # Shared instance
+    shared_instance = ContextInstanceActivity.new
+    assert_equal %w[interceptor-init interceptor-execute execute],
+                 execute_activity(shared_instance, interceptors: [ContextInstanceInterceptor.new])
+    assert_equal %w[interceptor-init interceptor-execute execute interceptor-init interceptor-execute execute],
+                 execute_activity(shared_instance, interceptors: [ContextInstanceInterceptor.new])
+  end
+
   # steep:ignore
   def execute_activity(
     activity,
diff --git a/temporalio/test/worker_workflow_test.rb b/temporalio/test/worker_workflow_test.rb
index ff6491ca..50a5100f 100644
--- a/temporalio/test/worker_workflow_test.rb
+++ b/temporalio/test/worker_workflow_test.rb
@@ -1738,6 +1738,37 @@ def test_confirm_garbage_collect
     end
   end
 
+  class ContextInstanceInterceptor
+    include Temporalio::Worker::Interceptor::Workflow
+
+    def intercept_workflow(next_interceptor)
+      Inbound.new(next_interceptor)
+    end
+
+    class Inbound < Temporalio::Worker::Interceptor::Workflow::Inbound
+      def execute(input)
+        Temporalio::Workflow.instance.events << 'interceptor-execute'
+        super
+      end
+    end
+  end
+
+  class ContextInstanceWorkflow < Temporalio::Workflow::Definition
+    def execute
+      events << 'execute'
+    end
+
+    workflow_query
+    def events
+      @events ||= []
+    end
+  end
+
+  def test_context_instance
+    assert_equal %w[interceptor-execute execute],
+                 execute_workflow(ContextInstanceWorkflow, interceptors: [ContextInstanceInterceptor.new])
+  end
+
   # TODO(cretz): To test
   # * Common
   #   * Eager workflow start
diff --git a/temporalio/test/workflow_utils.rb b/temporalio/test/workflow_utils.rb
index 92d896d4..61afc0b2 100644
--- a/temporalio/test/workflow_utils.rb
+++ b/temporalio/test/workflow_utils.rb
@@ -27,7 +27,8 @@ def execute_workflow(
     workflow_payload_codec_thread_pool: nil,
     id_conflict_policy: Temporalio::WorkflowIDConflictPolicy::UNSPECIFIED,
     max_heartbeat_throttle_interval: 60.0,
-    task_timeout: nil
+    task_timeout: nil,
+    interceptors: []
   )
     worker = Temporalio::Worker.new(
       client:,
@@ -38,7 +39,8 @@ def execute_workflow(
       max_cached_workflows:,
       logger: logger || client.options.logger,
       workflow_payload_codec_thread_pool:,
-      max_heartbeat_throttle_interval:
+      max_heartbeat_throttle_interval:,
+      interceptors:
     )
     worker.run do
       handle = client.start_workflow(