diff --git a/server/src/main/java/org/elasticsearch/TransportVersions.java b/server/src/main/java/org/elasticsearch/TransportVersions.java
index fc4323e418b72..e3f4f99ee0425 100644
--- a/server/src/main/java/org/elasticsearch/TransportVersions.java
+++ b/server/src/main/java/org/elasticsearch/TransportVersions.java
@@ -184,6 +184,7 @@ static TransportVersion def(int id) {
     public static final TransportVersion ADD_RESOURCE_ALREADY_UPLOADED_EXCEPTION = def(8_643_00_0);
     public static final TransportVersion ESQL_MV_ORDERING_SORTED_ASCENDING = def(8_644_00_0);
     public static final TransportVersion ESQL_PAGE_MAPPING_TO_ITERATOR = def(8_645_00_0);
+    public static final TransportVersion ML_QUESTION_ANSWERING_CONFIG_REQUIRE_QUESTION_NON_NULL = def(8_646_00_0);
 
     /*
      * STOP! READ THIS FIRST! No, really,
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/inference/trainedmodel/QuestionAnsweringConfig.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/inference/trainedmodel/QuestionAnsweringConfig.java
index 134933deab917..02baa5f715223 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/inference/trainedmodel/QuestionAnsweringConfig.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/inference/trainedmodel/QuestionAnsweringConfig.java
@@ -148,7 +148,11 @@ public QuestionAnsweringConfig(StreamInput in) throws IOException {
         vocabularyConfig = new VocabularyConfig(in);
         tokenization = in.readNamedWriteable(Tokenization.class);
         resultsField = in.readOptionalString();
-        question = in.readOptionalString();
+        if (in.getTransportVersion().onOrAfter(TransportVersions.ML_QUESTION_ANSWERING_CONFIG_REQUIRE_QUESTION_NON_NULL)) {
+            question = in.readString();
+        } else {
+            question = in.readOptionalString();
+        }
     }
 
     @Override
@@ -158,7 +162,11 @@ public void writeTo(StreamOutput out) throws IOException {
         vocabularyConfig.writeTo(out);
         out.writeNamedWriteable(tokenization);
         out.writeOptionalString(resultsField);
-        out.writeOptionalString(question);
+        if (out.getTransportVersion().onOrAfter(TransportVersions.ML_QUESTION_ANSWERING_CONFIG_REQUIRE_QUESTION_NON_NULL)) {
+            out.writeString(question);
+        } else {
+            out.writeOptionalString(question);
+        }
     }
 
     @Override
@@ -171,9 +179,7 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
         if (resultsField != null) {
             builder.field(RESULTS_FIELD.getPreferredName(), resultsField);
         }
-        if (question != null) {
-            builder.field(QUESTION.getPreferredName(), question);
-        }
+        builder.field(QUESTION.getPreferredName(), question);
         builder.endObject();
         return builder;
     }
diff --git a/x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ml/inference/trainedmodel/QuestionAnsweringConfigUpdateTests.java b/x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ml/inference/trainedmodel/QuestionAnsweringConfigUpdateTests.java
index e787b770b5da5..800eb1a3797b9 100644
--- a/x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ml/inference/trainedmodel/QuestionAnsweringConfigUpdateTests.java
+++ b/x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ml/inference/trainedmodel/QuestionAnsweringConfigUpdateTests.java
@@ -35,6 +35,7 @@ public static QuestionAnsweringConfigUpdate randomUpdate() {
         );
     }
 
+    // TODO add test for question
     public static QuestionAnsweringConfigUpdate mutateForVersion(QuestionAnsweringConfigUpdate instance, TransportVersion version) {
         if (version.before(TransportVersions.V_8_1_0)) {
             return new QuestionAnsweringConfigUpdate(
@@ -45,6 +46,15 @@ public static QuestionAnsweringConfigUpdate mutateForVersion(QuestionAnsweringCo
                 null
             );
         }
+        if (version.before(TransportVersions.ML_QUESTION_ANSWERING_CONFIG_REQUIRE_QUESTION_NON_NULL)) {
+            return new QuestionAnsweringConfigUpdate(
+                instance.getQuestion() == null ? instance.getQuestion() : null,
+                instance.getNumTopClasses(),
+                instance.getMaxAnswerLength(),
+                instance.getResultsField(),
+                instance.getTokenizationUpdate()
+            );
+        }
         return instance;
     }
 
diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/tokenizers/BertTokenizer.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/tokenizers/BertTokenizer.java
index 45571ea2a8238..464c8eac8c9dd 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/tokenizers/BertTokenizer.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/tokenizers/BertTokenizer.java
@@ -236,6 +236,10 @@ public NlpTask.RequestBuilder requestBuilder() {
         ).buildRequest(requestId, truncate);
     }
 
+    /**
+     * @param seq cannot be null
+     * @return InnerTokenization
+     */
     @Override
     public InnerTokenization innerTokenize(String seq) {
         List<Integer> tokenPositionMap = new ArrayList<>();
diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/tokenizers/RobertaTokenizer.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/tokenizers/RobertaTokenizer.java
index d604b52a55cc4..e884e84faa85d 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/tokenizers/RobertaTokenizer.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/tokenizers/RobertaTokenizer.java
@@ -178,6 +178,10 @@ TokenizationResult.TokensBuilder createTokensBuilder(int clsTokenId, int sepToke
         return new RobertaTokenizationResult.RobertaTokensBuilder(withSpecialTokens, clsTokenId, sepTokenId);
     }
 
+    /**
+     * @param seq cannot be null
+     * @return InnerTokenization
+     */
     @Override
     public InnerTokenization innerTokenize(String seq) {
         List<Integer> tokenPositionMap = new ArrayList<>();
diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/tokenizers/XLMRobertaTokenizer.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/tokenizers/XLMRobertaTokenizer.java
index 3c7d54cd547bf..7a856d8e4735a 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/tokenizers/XLMRobertaTokenizer.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/tokenizers/XLMRobertaTokenizer.java
@@ -173,6 +173,10 @@ TokenizationResult.TokensBuilder createTokensBuilder(int clsTokenId, int sepToke
         return new XLMRobertaTokenizationResult.XLMRobertaTokensBuilder(withSpecialTokens, clsTokenId, sepTokenId);
     }
 
+    /**
+     * @param seq cannot be null
+     * @return InnerTokenization
+     */
     @Override
     public InnerTokenization innerTokenize(String seq) {
         List<Integer> tokenPositionMap = new ArrayList<>();