diff --git a/app/graphql/timdex_schema.rb b/app/graphql/timdex_schema.rb
index 697f5ec..1d2f19f 100644
--- a/app/graphql/timdex_schema.rb
+++ b/app/graphql/timdex_schema.rb
@@ -3,4 +3,26 @@ class TimdexSchema < GraphQL::Schema
   trace_class(GraphQL::Tracing::LegacyTrace)
 
   query(Types::QueryType)
+
+  use GraphQL::Schema::Visibility
+
+  # Hide arguments marked as "INTERNAL USE ONLY" from introspection queries
+  def self.visible?(member, context)
+    # 1. Detect if the member is one of your internal arguments
+    if member.respond_to?(:description) && member.description&.include?('INTERNAL USE ONLY')
+
+      # 2. Extract the root operation fields being requested
+      selected_fields = context.query&.selected_operation&.selections || []
+
+      # 3. Check if any root field is an introspection entrypoint (__schema or __type)
+      is_introspection = selected_fields.any? do |selection|
+        selection.respond_to?(:name) && %w[__schema __type].include?(selection.name)
+      end
+
+      # 4. Hide the arguments if GraphiQL/Introspection is sniffing the schema
+      return false if is_introspection
+    end
+
+    super
+  end
 end
diff --git a/app/graphql/types/query_type.rb b/app/graphql/types/query_type.rb
index 4aff58b..62b32dd 100644
--- a/app/graphql/types/query_type.rb
+++ b/app/graphql/types/query_type.rb
@@ -105,18 +105,38 @@ def record_id(id:, index:)
       argument :subjects_filter, [String], required: false, default_value: nil,
                                            description: 'Filter by subject terms. Use the `contentType` aggregation ' \
                                                         'for a list of possible values. Multiple values are ANDed.'
+
+      # Internal semantic query tuning parameters (not documented publicly). Must start with `INTERNAL USE ONLY` to be
+      # excluded from public documentation.
+      argument :semantic_must_boost_threshold, Float, required: false, default_value: nil,
+                                                      description: 'INTERNAL USE ONLY: Semantic query must boost ' \
+                                                                   'threshold (0.0-1.0)'
+      argument :semantic_drop_boost_threshold, Float, required: false, default_value: nil,
+                                                      description: 'INTERNAL USE ONLY: Semantic query drop boost ' \
+                                                                   'threshold (0.0-1.0)'
+      argument :semantic_short_query_max_tokens, Integer, required: false, default_value: nil,
+                                                          description: 'INTERNAL USE ONLY: Semantic query short ' \
+                                                                       'query max tokens'
     end
 
     def search(searchterm:, citation:, contributors:, funding_information:, geodistance:, geobox:, identifiers:,
                locations:, subjects:, title:, index:, source:, from:, boolean_type:, fulltext:, per_page: 20,
-               query_mode: 'keyword', use_global_scoring: false, **filters)
+               query_mode: 'keyword', use_global_scoring: false, semantic_must_boost_threshold: nil,
+               semantic_drop_boost_threshold: nil, semantic_short_query_max_tokens: nil, **filters)
       query = construct_query(searchterm, citation, contributors, funding_information, geodistance, geobox, identifiers,
                               locations, subjects, title, source, boolean_type, filters, per_page, query_mode)
 
+      semantic_options = {
+        must_boost_threshold: semantic_must_boost_threshold,
+        drop_boost_threshold: semantic_drop_boost_threshold,
+        short_query_max_tokens: semantic_short_query_max_tokens
+      }
+
       results = Opensearch.new.search(from, query, Timdex::OSClient, highlight: highlight_requested?, index: index,
                                                                      fulltext: fulltext, query_mode: query_mode,
                                                                      requested_aggregations: requested_aggregations,
-                                                                     use_global_scoring: use_global_scoring)
+                                                                     use_global_scoring: use_global_scoring,
+                                                                     semantic_options: semantic_options)
 
       response = {}
       response[:hits] = results['hits']['total']['value']
diff --git a/app/models/hybrid_query_builder.rb b/app/models/hybrid_query_builder.rb
index ddc4a88..4f791a8 100644
--- a/app/models/hybrid_query_builder.rb
+++ b/app/models/hybrid_query_builder.rb
@@ -1,5 +1,5 @@
 class HybridQueryBuilder
-  def build(params, fulltext: false)
+  def build(params, fulltext: false, semantic_options: {})
     query_text = params[:q].to_s.strip
 
     lexical_query = LexicalQueryBuilder.new.build(params, fulltext: fulltext)
@@ -8,7 +8,7 @@ def build(params, fulltext: false)
     return lexical_query if query_text.blank?
 
     begin
-      semantic_query = SemanticQueryBuilder.new.build(params, fulltext: fulltext)
+      semantic_query = SemanticQueryBuilder.new.build(params, fulltext: fulltext, semantic_options: semantic_options)
 
       # Both succeeded - combine them with should clause while preserving filters
       combine_queries(semantic_query, lexical_query)
diff --git a/app/models/opensearch.rb b/app/models/opensearch.rb
index da0e413..2ac492a 100644
--- a/app/models/opensearch.rb
+++ b/app/models/opensearch.rb
@@ -4,12 +4,13 @@ class Opensearch
   MAX_SIZE = 200
 
   def search(from, params, client, highlight: false, index: nil, fulltext: false, query_mode: 'keyword',
-             requested_aggregations: [], use_global_scoring: false)
+             requested_aggregations: [], use_global_scoring: false, semantic_options: {})
     @params = params
     @highlight = highlight
     @fulltext = fulltext?(fulltext)
     @query_mode = query_mode
     @requested_aggregations = requested_aggregations
+    @semantic_options = semantic_options
     index = default_index unless index.present?
     search_params = { index:, body: build_query(from) }
     search_params[:search_type] = 'dfs_query_then_fetch' if use_global_scoring
@@ -69,7 +70,12 @@ def query
                 LexicalQueryBuilder.new
               end
 
-    builder.build(@params, fulltext: @fulltext)
+    # Only pass semantic_options to builders that support it (semantic and hybrid)
+    if @query_mode.in?(%w[semantic hybrid])
+      builder.build(@params, fulltext: @fulltext, semantic_options: @semantic_options || {})
+    else
+      builder.build(@params, fulltext: @fulltext)
+    end
   end
 
   def sort_builder
diff --git a/app/models/semantic_query_builder.rb b/app/models/semantic_query_builder.rb
index dafffe3..dd83e34 100644
--- a/app/models/semantic_query_builder.rb
+++ b/app/models/semantic_query_builder.rb
@@ -2,7 +2,7 @@ class SemanticQueryBuilder
   # Dedicated exception for Lambda invocation failures (not parsing/validation errors)
   class LambdaError < StandardError; end
 
-  def build(params, fulltext: false)
+  def build(params, fulltext: false, semantic_options: {})
     query_text = params[:q].to_s.strip
 
     # If no query text provided, return a match_all query with filters applied
@@ -14,7 +14,8 @@ def build(params, fulltext: false)
       return { match_all: {} }
     end
 
-    lambda_response = invoke_semantic_builder(query_text)
+    lambda_response = invoke_semantic_builder(query_text, semantic_options)
+
     semantic_query = parse_lambda_response(lambda_response)
 
     # Validate the query structure has a bool clause before applying filters
@@ -31,8 +32,23 @@ def build(params, fulltext: false)
 
   private
 
-  def invoke_semantic_builder(query_text)
+  def invoke_semantic_builder(query_text, semantic_options = {})
     payload = { query: query_text }
+
+    # Add optional semantic tuning parameters if provided
+    if semantic_options[:must_boost_threshold].present?
+      payload[:must_boost_threshold] =
+        semantic_options[:must_boost_threshold]
+    end
+    if semantic_options[:drop_boost_threshold].present?
+      payload[:drop_boost_threshold] =
+        semantic_options[:drop_boost_threshold]
+    end
+    if semantic_options[:short_query_max_tokens].present?
+      payload[:short_query_max_tokens] =
+        semantic_options[:short_query_max_tokens]
+    end
+
     function_name = ENV.fetch('TIMDEX_SEMANTIC_BUILDER_FUNCTION_NAME')
 
     begin
diff --git a/test/controllers/graphql_controller_test.rb b/test/controllers/graphql_controller_test.rb
index e4c723a..3f8484b 100644
--- a/test/controllers/graphql_controller_test.rb
+++ b/test/controllers/graphql_controller_test.rb
@@ -1224,4 +1224,96 @@ class GraphqlControllerTest < ActionDispatch::IntegrationTest
                               }' }
     assert_equal(200, response.status)
   end
+
+  test 'graphql introspection hides internal semantic arguments via __schema' do
+    post '/graphql', params: { query: '{
+                                __schema {
+                                  queryType {
+                                    fields(includeDeprecated: true) {
+                                      name
+                                      args {
+                                        name
+                                      }
+                                    }
+                                  }
+                                }
+                              }' }
+    assert_equal(200, response.status)
+    json = JSON.parse(response.body)
+
+    # Find the 'search' field
+    search_field = json['data']['__schema']['queryType']['fields'].find { |f| f['name'] == 'search' }
+    assert(search_field, 'search field should exist in schema')
+
+    # Get all argument names for the search field
+    arg_names = search_field['args'].map { |arg| arg['name'] }
+
+    # Verify internal semantic arguments are NOT present
+    assert_not_includes arg_names, 'semanticMustBoostThreshold'
+    assert_not_includes arg_names, 'semanticDropBoostThreshold'
+    assert_not_includes arg_names, 'semanticShortQueryMaxTokens'
+
+    # Verify other expected arguments ARE present
+    assert_includes arg_names, 'searchterm'
+    assert_includes arg_names, 'sourceFilter'
+  end
+
+  test 'graphql introspection hides internal semantic arguments via __type' do
+    post '/graphql', params: { query: '{
+                                __type(name: "Query") {
+                                  fields(includeDeprecated: true) {
+                                    name
+                                    args {
+                                      name
+                                    }
+                                  }
+                                }
+                              }' }
+    assert_equal(200, response.status)
+    json = JSON.parse(response.body)
+
+    # Find the 'search' field
+    search_field = json['data']['__type']['fields'].find { |f| f['name'] == 'search' }
+    assert(search_field, 'search field should exist in Query type')
+
+    # Get all argument names for the search field
+    arg_names = search_field['args'].map { |arg| arg['name'] }
+
+    # Verify internal semantic arguments are NOT present
+    assert_not_includes arg_names, 'semanticMustBoostThreshold'
+    assert_not_includes arg_names, 'semanticDropBoostThreshold'
+    assert_not_includes arg_names, 'semanticShortQueryMaxTokens'
+
+    # Verify other expected arguments ARE present
+    assert_includes arg_names, 'searchterm'
+    assert_includes arg_names, 'sourceFilter'
+  end
+
+  test 'graphql internal semantic arguments still work in actual queries' do
+    VCR.use_cassette('opensearch init') do
+      VCR.use_cassette('graphql search data analytics') do
+        # Verify that the arguments work when sent in a real query
+        # (they are just hidden from introspection)
+        post '/graphql', params: { query: '{
+                                    search(
+                                      searchterm: "data analytics",
+                                      semanticMustBoostThreshold: 0.5,
+                                      semanticDropBoostThreshold: 0.2,
+                                      semanticShortQueryMaxTokens: 10
+                                    ) {
+                                      records {
+                                        title
+                                      }
+                                    }
+                                  }' }
+        assert_equal(200, response.status)
+        json = JSON.parse(response.body)
+
+        # Verify the query succeeded and returned records
+        assert_nil json['errors'], "Query should not have errors: #{json['errors']}"
+        assert_equal('Data analytics and big data',
+                     json['data']['search']['records'].first['title'])
+      end
+    end
+  end
 end
diff --git a/test/models/semantic_query_builder_test.rb b/test/models/semantic_query_builder_test.rb
index 756511f..b8ae9b9 100644
--- a/test/models/semantic_query_builder_test.rb
+++ b/test/models/semantic_query_builder_test.rb
@@ -198,4 +198,186 @@ def setup_mock_lambda(response_data)
     assert_includes result[:bool].keys, :filter
     assert_equal [], result[:bool][:filter]
   end
+
+  # Tests for semantic_options in Lambda payload
+
+  test 'includes semantic options in lambda payload' do
+    query_text = 'test query'
+    mock_response = {
+      'query' => {
+        'bool' => {
+          'should' => [
+            { 'rank_feature' => { 'field' => 'embedding_full_record.test', 'boost' => 5.0 } }
+          ]
+        }
+      }
+    }
+
+    captured_payload = nil
+    Aws::Lambda::Client.any_instance.expects(:invoke).with do |args|
+      captured_payload = JSON.parse(args[:payload])
+      true
+    end.returns(Struct.new(:payload).new(StringIO.new(mock_response.to_json)))
+
+    params = { q: query_text }
+    semantic_options = { must_boost_threshold: 0.5 }
+    @builder.build(params, semantic_options: semantic_options)
+
+    # Verify the payload contains the semantic option
+    assert_equal 0.5, captured_payload['must_boost_threshold']
+  end
+
+  test 'includes multiple semantic options in lambda payload' do
+    query_text = 'test query'
+    mock_response = {
+      'query' => {
+        'bool' => {
+          'should' => [
+            { 'rank_feature' => { 'field' => 'embedding_full_record.test', 'boost' => 5.0 } }
+          ]
+        }
+      }
+    }
+
+    captured_payload = nil
+    Aws::Lambda::Client.any_instance.expects(:invoke).with do |args|
+      captured_payload = JSON.parse(args[:payload])
+      true
+    end.returns(Struct.new(:payload).new(StringIO.new(mock_response.to_json)))
+
+    params = { q: query_text }
+    semantic_options = {
+      must_boost_threshold: 0.5,
+      drop_boost_threshold: 0.2,
+      short_query_max_tokens: 10
+    }
+    @builder.build(params, semantic_options: semantic_options)
+
+    # Verify all semantic options are in the payload
+    assert_equal 0.5, captured_payload['must_boost_threshold']
+    assert_equal 0.2, captured_payload['drop_boost_threshold']
+    assert_equal 10, captured_payload['short_query_max_tokens']
+  end
+
+  test 'omits nil semantic options from lambda payload' do
+    query_text = 'test query'
+    mock_response = {
+      'query' => {
+        'bool' => {
+          'should' => [
+            { 'rank_feature' => { 'field' => 'embedding_full_record.test', 'boost' => 5.0 } }
+          ]
+        }
+      }
+    }
+
+    captured_payload = nil
+    Aws::Lambda::Client.any_instance.expects(:invoke).with do |args|
+      captured_payload = JSON.parse(args[:payload])
+      true
+    end.returns(Struct.new(:payload).new(StringIO.new(mock_response.to_json)))
+
+    params = { q: query_text }
+    semantic_options = {
+      must_boost_threshold: 0.5,
+      drop_boost_threshold: nil,
+      short_query_max_tokens: nil
+    }
+    @builder.build(params, semantic_options: semantic_options)
+
+    # Verify only non-nil options are in the payload
+    assert_equal 0.5, captured_payload['must_boost_threshold']
+    # Verify they are not keys in the payload hash
+    refute captured_payload.key?('drop_boost_threshold')
+    refute captured_payload.key?('short_query_max_tokens')
+  end
+
+  test 'omits empty string semantic options from lambda payload' do
+    query_text = 'test query'
+    mock_response = {
+      'query' => {
+        'bool' => {
+          'should' => [
+            { 'rank_feature' => { 'field' => 'embedding_full_record.test', 'boost' => 5.0 } }
+          ]
+        }
+      }
+    }
+
+    captured_payload = nil
+    Aws::Lambda::Client.any_instance.expects(:invoke).with do |args|
+      captured_payload = JSON.parse(args[:payload])
+      true
+    end.returns(Struct.new(:payload).new(StringIO.new(mock_response.to_json)))
+
+    params = { q: query_text }
+    semantic_options = {
+      must_boost_threshold: '',
+      drop_boost_threshold: 0.2
+    }
+    @builder.build(params, semantic_options: semantic_options)
+
+    # Verify empty string options are not included
+    refute captured_payload.key?('must_boost_threshold')
+    assert_equal 0.2, captured_payload['drop_boost_threshold']
+  end
+
+  test 'includes only query key when no semantic options provided' do
+    query_text = 'test query'
+    mock_response = {
+      'query' => {
+        'bool' => {
+          'should' => [
+            { 'rank_feature' => { 'field' => 'embedding_full_record.test', 'boost' => 5.0 } }
+          ]
+        }
+      }
+    }
+
+    captured_payload = nil
+    Aws::Lambda::Client.any_instance.expects(:invoke).with do |args|
+      captured_payload = JSON.parse(args[:payload])
+      true
+    end.returns(Struct.new(:payload).new(StringIO.new(mock_response.to_json)))
+
+    params = { q: query_text }
+    @builder.build(params, semantic_options: {})
+
+    # Verify only query key is in the payload
+    assert_equal({ 'query' => query_text }, captured_payload)
+  end
+
+  test 'semantic options payload contains both query and options' do
+    query_text = 'test query'
+    mock_response = {
+      'query' => {
+        'bool' => {
+          'should' => [
+            { 'rank_feature' => { 'field' => 'embedding_full_record.test', 'boost' => 5.0 } }
+          ]
+        }
+      }
+    }
+
+    captured_payload = nil
+    Aws::Lambda::Client.any_instance.expects(:invoke).with do |args|
+      captured_payload = JSON.parse(args[:payload])
+      true
+    end.returns(Struct.new(:payload).new(StringIO.new(mock_response.to_json)))
+
+    params = { q: query_text }
+    semantic_options = {
+      must_boost_threshold: 0.75,
+      short_query_max_tokens: 5
+    }
+    @builder.build(params, semantic_options: semantic_options)
+
+    # Verify payload structure contains query and both options
+    expected_payload = {
+      'query' => query_text,
+      'must_boost_threshold' => 0.75,
+      'short_query_max_tokens' => 5
+    }
+    assert_equal expected_payload, captured_payload
+  end
 end