Read max model length from nested fields in config.json

src/llm/servable_initializer.cpp

@@ -532,6 +532,20 @@ Status parseModelsPath(std::string& outPath, std::string modelsPath, std::string
     return StatusCode::LLM_NODE_PATH_DOES_NOT_EXIST_AND_NOT_GGUFFILE;
 }
 
+static std::optional<uint32_t> findMaxLengthField(const rapidjson::Value& config) {
+    if (!config.IsObject()) {
+        return std::nullopt;
+    }
+    static const std::vector<std::string> maxLengthFields = {"max_position_embeddings", "n_positions", "seq_len", "seq_length", "n_ctx", "sliding_window"};
+    for (const auto& field : maxLengthFields) {
+        auto it = config.FindMember(field.c_str());
+        if (it != config.MemberEnd() && it->value.IsUint()) {
+            return it->value.GetUint();
+        }
+    }
+    return std::nullopt;
+}
+
 std::optional<uint32_t> parseMaxModelLength(std::string& modelsPath) {
     std::string configPath = FileSystem::appendSlash(modelsPath) + "config.json";
     std::optional<uint32_t> maxModelLength;
@@ -546,12 +560,11 @@ std::optional<uint32_t> parseMaxModelLength(std::string& modelsPath) {
         if (parseResult.Code()) {
             return maxModelLength;
         }
-        std::vector<std::string> maxLengthFields = {"max_position_embeddings", "n_positions", "seq_len", "seq_length", "n_ctx", "sliding_window"};
-        for (auto field : maxLengthFields) {
-            if (modelConfig.HasMember(field.c_str()) && modelConfig[field.c_str()].IsUint()) {
-                maxModelLength = modelConfig[field.c_str()].GetUint();
-                break;
-            }
+        maxModelLength = findMaxLengthField(modelConfig);
+        // Composite VLM/omni configs (e.g. Qwen3.5-Omni) nest the language model's
+        // parameters under "text_config" instead of the top level.
+        if (!maxModelLength.has_value() && modelConfig.HasMember("text_config") && modelConfig["text_config"].IsObject()) {
+            maxModelLength = findMaxLengthField(modelConfig["text_config"]);
         }
     }
     return maxModelLength;

src/test/llm/max_model_length_test.cpp

@@ -142,3 +142,27 @@ TEST_F(MaxModelLengthTest, maxModelLength_parsingOrder) {
     ASSERT_TRUE(maxModelLength.has_value());
     EXPECT_EQ(maxModelLength.value(), 5);
 }
+
+TEST_F(MaxModelLengthTest, maxModelLength_textConfig_VALID) {
+    // Composite VLM/omni configs (e.g. Qwen3.5-Omni) nest the field under "text_config".
+    std::string modelConfigContent = R"({"model_type" : "qwen3_5", "text_config" : {"max_position_embeddings" : 262144}})";
+    createConfigFileWithContent(modelConfigContent, configFilePath);
+    auto maxModelLength = parseMaxModelLength(directoryPath);
+    ASSERT_TRUE(maxModelLength.has_value());
+    EXPECT_EQ(maxModelLength.value(), 262144);
+}
+
+TEST_F(MaxModelLengthTest, maxModelLength_topLevelTakesPriorityOverTextConfig) {
+    std::string modelConfigContent = R"({"max_position_embeddings" : 5, "text_config" : {"max_position_embeddings" : 262144}})";
+    createConfigFileWithContent(modelConfigContent, configFilePath);
+    auto maxModelLength = parseMaxModelLength(directoryPath);
+    ASSERT_TRUE(maxModelLength.has_value());
+    EXPECT_EQ(maxModelLength.value(), 5);
+}
+
+TEST_F(MaxModelLengthTest, maxModelLength_textConfig_notAnObject) {
+    std::string modelConfigContent = R"({"text_config" : "INVALID"})";
+    createConfigFileWithContent(modelConfigContent, configFilePath);
+    auto maxModelLength = parseMaxModelLength(directoryPath);
+    EXPECT_FALSE(maxModelLength.has_value());
+}