diff --git a/models/spring-ai-openai/src/main/java/org/springframework/ai/openai/OpenAiChatOptions.java b/models/spring-ai-openai/src/main/java/org/springframework/ai/openai/OpenAiChatOptions.java
index 703134b509c..3dc6b23b020 100644
--- a/models/spring-ai-openai/src/main/java/org/springframework/ai/openai/OpenAiChatOptions.java
+++ b/models/spring-ai-openai/src/main/java/org/springframework/ai/openai/OpenAiChatOptions.java
@@ -25,6 +25,8 @@
 import java.util.Objects;
 import java.util.Set;
 
+import com.fasterxml.jackson.annotation.JsonAnyGetter;
+import com.fasterxml.jackson.annotation.JsonAnySetter;
 import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.annotation.JsonInclude.Include;
@@ -292,7 +294,7 @@ public class OpenAiChatOptions implements ToolCallingChatOptions {
 	 *     .build()
 	 * }</pre>
 	 */
-	private @JsonProperty("extra_body") Map<String, Object> extraBody;
+	private Map<String, Object> extraBody = new HashMap<>();
 
 	// @formatter:on
 
@@ -338,7 +340,7 @@ public static OpenAiChatOptions fromOptions(OpenAiChatOptions fromOptions) {
 			.serviceTier(fromOptions.getServiceTier())
 			.promptCacheKey(fromOptions.getPromptCacheKey())
 			.safetyIdentifier(fromOptions.getSafetyIdentifier())
-			.extraBody(fromOptions.getExtraBody())
+			.extraBody(fromOptions.extraBody())
 			.build();
 	}
 
@@ -535,12 +537,29 @@ public void setParallelToolCalls(Boolean parallelToolCalls) {
 		this.parallelToolCalls = parallelToolCalls;
 	}
 
-	public Map<String, Object> getExtraBody() {
+	/**
+	 * Overrides the default accessor to add @JsonAnyGetter annotation. This causes
+	 * Jackson to flatten the extraBody map contents to the top level of the JSON,
+	 * matching the behavior expected by OpenAI-compatible servers like vLLM, Ollama, etc.
+	 * @return The extraBody map, or null if not set.
+	 */
+	@JsonAnyGetter
+	public Map<String, Object> extraBody() {
 		return this.extraBody;
 	}
 
-	public void setExtraBody(Map<String, Object> extraBody) {
-		this.extraBody = extraBody;
+	/**
+	 * Handles deserialization of unknown properties into the extraBody map. This enables
+	 * JSON with extra fields to be deserialized into ChatCompletionRequest, which is
+	 * useful for implementing OpenAI API proxy servers with @RestController.
+	 * @param key The property name
+	 * @param value The property value
+	 */
+	@JsonAnySetter
+	private void setExtraBodyProperty(String key, Object value) {
+		if (this.extraBody != null) {
+			this.extraBody.put(key, value);
+		}
 	}
 
 	@Override
diff --git a/spring-ai-model/src/main/java/org/springframework/ai/model/ModelOptionsUtils.java b/spring-ai-model/src/main/java/org/springframework/ai/model/ModelOptionsUtils.java
index 079c8089ee5..dda307236ae 100644
--- a/spring-ai-model/src/main/java/org/springframework/ai/model/ModelOptionsUtils.java
+++ b/spring-ai-model/src/main/java/org/springframework/ai/model/ModelOptionsUtils.java
@@ -18,6 +18,7 @@
 
 import java.beans.PropertyDescriptor;
 import java.lang.reflect.Field;
+import java.lang.reflect.Method;
 import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -28,6 +29,7 @@
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.stream.Collectors;
 
+import com.fasterxml.jackson.annotation.JsonAnyGetter;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.core.type.TypeReference;
@@ -83,7 +85,7 @@ public abstract class ModelOptionsUtils {
 
 	private static final List<String> BEAN_MERGE_FIELD_EXCISIONS = List.of("class");
 
-	private static final ConcurrentHashMap<Class<?>, List<String>> REQUEST_FIELD_NAMES_PER_CLASS = new ConcurrentHashMap<>();
+	private static final ConcurrentHashMap<Class<?>, JsonPropertyResult> REQUEST_FIELD_NAMES_PER_CLASS = new ConcurrentHashMap<>();
 
 	private static final AtomicReference<SchemaGenerator> SCHEMA_GENERATOR_CACHE = new AtomicReference<>();
 
@@ -182,10 +184,14 @@ public static <T> T merge(Object source, Object target, Class<T> clazz, List<Str
 		}
 
 		List<String> requestFieldNames = CollectionUtils.isEmpty(acceptedFieldNames)
-				? REQUEST_FIELD_NAMES_PER_CLASS.computeIfAbsent(clazz, ModelOptionsUtils::getJsonPropertyValues)
+				? REQUEST_FIELD_NAMES_PER_CLASS.computeIfAbsent(clazz, ModelOptionsUtils::getJsonPropertyResult)
+					.properties()
 				: acceptedFieldNames;
 
-		if (CollectionUtils.isEmpty(requestFieldNames)) {
+		boolean acceptAllFields = REQUEST_FIELD_NAMES_PER_CLASS.containsKey(clazz)
+				&& REQUEST_FIELD_NAMES_PER_CLASS.get(clazz).acceptAllFields;
+
+		if (!acceptAllFields && CollectionUtils.isEmpty(requestFieldNames)) {
 			throw new IllegalArgumentException("No @JsonProperty fields found in the " + clazz.getName());
 		}
 
@@ -199,7 +205,7 @@ public static <T> T merge(Object source, Object target, Class<T> clazz, List<Str
 
 		targetMap = targetMap.entrySet()
 			.stream()
-			.filter(e -> requestFieldNames.contains(e.getKey()))
+			.filter(e -> acceptAllFields || requestFieldNames.contains(e.getKey()))
 			.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
 
 		return ModelOptionsUtils.mapToClass(targetMap, clazz);
@@ -263,20 +269,34 @@ public static <T> T mapToClass(Map<String, Object> source, Class<T> clazz) {
 	}
 
 	/**
-	 * Returns the list of name values of the {@link JsonProperty} annotations.
+	 * Returns the result contains tag of accept all fields or list of json fields.
 	 * @param clazz the class that contains fields annotated with {@link JsonProperty}.
-	 * @return the list of values of the {@link JsonProperty} annotations.
+	 * @return the result contains tag of method has {@link JsonAnyGetter} annotation or
+	 * list of values of the {@link JsonProperty} annotations.
 	 */
-	public static List<String> getJsonPropertyValues(Class<?> clazz) {
+	public static JsonPropertyResult getJsonPropertyResult(Class<?> clazz) {
 		List<String> values = new ArrayList<>();
 		Field[] fields = clazz.getDeclaredFields();
+		Method[] methods = clazz.getDeclaredMethods();
+		boolean hasAnyGetter = false;
+
+		for (Method method : methods) {
+			// Iterate through the method to check JsonAnyGetter annotation to ensure that
+			// unknown parameters can be copied
+			JsonAnyGetter anyGetterAnnotation = method.getAnnotation(JsonAnyGetter.class);
+			if (anyGetterAnnotation != null) {
+				hasAnyGetter = true;
+				return new JsonPropertyResult(hasAnyGetter, values);
+			}
+		}
+
 		for (Field field : fields) {
 			JsonProperty jsonPropertyAnnotation = field.getAnnotation(JsonProperty.class);
 			if (jsonPropertyAnnotation != null) {
 				values.add(jsonPropertyAnnotation.value());
 			}
 		}
-		return values;
+		return new JsonPropertyResult(false, values);
 	}
 
 	/**
@@ -452,4 +472,13 @@ public static <T> T mergeOption(T runtimeValue, T defaultValue) {
 		return ObjectUtils.isEmpty(runtimeValue) ? defaultValue : runtimeValue;
 	}
 
+	/**
+	 * Record the decision result of {@link #getJsonPropertyResult(Class)}
+	 *
+	 * @param acceptAllFields the current class allows tags for all properties
+	 * @param properties list of properties allowed by the current class
+	 */
+	public record JsonPropertyResult(boolean acceptAllFields, List<String> properties) {
+	}
+
 }
diff --git a/spring-ai-model/src/test/java/org/springframework/ai/model/ModelOptionsUtilsTests.java b/spring-ai-model/src/test/java/org/springframework/ai/model/ModelOptionsUtilsTests.java
index 732a5cba1a4..91c7a047342 100644
--- a/spring-ai-model/src/test/java/org/springframework/ai/model/ModelOptionsUtilsTests.java
+++ b/spring-ai-model/src/test/java/org/springframework/ai/model/ModelOptionsUtilsTests.java
@@ -16,8 +16,11 @@
 
 package org.springframework.ai.model;
 
+import java.util.HashMap;
 import java.util.Map;
 
+import com.fasterxml.jackson.annotation.JsonAnyGetter;
+import com.fasterxml.jackson.annotation.JsonAnySetter;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.DeserializationFeature;
@@ -45,6 +48,9 @@ public void merge() {
 		specificOptions.setName("Mike");
 		specificOptions.setSpecificField("SpecificField");
 
+		TestSpecificOptions extraOptions = new TestSpecificOptions();
+		extraOptions.setExtraBodyProperty("key", "value");
+
 		assertThatThrownBy(
 				() -> ModelOptionsUtils.merge(portableOptions, specificOptions, TestPortableOptionsImpl.class))
 			.isInstanceOf(IllegalArgumentException.class)
@@ -56,6 +62,10 @@ public void merge() {
 		assertThat(specificOptions2.getName()).isEqualTo("John"); // !!! Overridden by the
 		// portableOptions
 		assertThat(specificOptions2.getSpecificField()).isEqualTo("SpecificField");
+
+		var extraSpecOptions = ModelOptionsUtils.merge(extraOptions, specificOptions, TestSpecificOptions.class);
+		assertThat(extraSpecOptions.extraBody()).containsKey("key");
+		assertThat(extraSpecOptions.extraBody().get("key")).isEqualTo("value");
 	}
 
 	@Test
@@ -171,12 +181,24 @@ public void pojo_emptyStringAsNullObject() throws Exception {
 	}
 
 	@Test
-	public void getJsonPropertyValues() {
+	public void getJsonPropertyResult() {
 		record TestRecord(@JsonProperty("field1") String fieldA, @JsonProperty("field2") String fieldB) {
 
 		}
-		assertThat(ModelOptionsUtils.getJsonPropertyValues(TestRecord.class)).hasSize(2);
-		assertThat(ModelOptionsUtils.getJsonPropertyValues(TestRecord.class)).containsExactly("field1", "field2");
+		assertThat(ModelOptionsUtils.getJsonPropertyResult(TestRecord.class).properties()).hasSize(2);
+		assertThat(ModelOptionsUtils.getJsonPropertyResult(TestRecord.class).properties()).containsExactly("field1",
+				"field2");
+
+		record TestAnyGetterRecord(Map<String, Object> extraBody) {
+
+			@JsonAnyGetter
+			public Map<String, Object> extraBody() {
+				return this.extraBody;
+			}
+		}
+
+		assertThat(ModelOptionsUtils.getJsonPropertyResult(TestAnyGetterRecord.class).acceptAllFields())
+			.isEqualTo(true);
 	}
 
 	@Test
@@ -357,6 +379,8 @@ public static class TestSpecificOptions implements TestPortableOptions {
 		@JsonProperty("age")
 		private Integer age;
 
+		private Map<String, Object> extraBody = new HashMap<>();
+
 		@Override
 		public String getName() {
 			return this.name;
@@ -385,6 +409,32 @@ public void setSpecificField(String modelSpecificField) {
 			this.specificField = modelSpecificField;
 		}
 
+		/**
+		 * Overrides the default accessor to add @JsonAnyGetter annotation. This causes
+		 * Jackson to flatten the extraBody map contents to the top level of the JSON,
+		 * matching the behavior expected by OpenAI-compatible servers like vLLM, Ollama,
+		 * etc.
+		 * @return The extraBody map, or null if not set.
+		 */
+		@JsonAnyGetter
+		public Map<String, Object> extraBody() {
+			return this.extraBody;
+		}
+
+		/**
+		 * Handles deserialization of unknown properties into the extraBody map. This
+		 * enables JSON with extra fields to be deserialized into ChatCompletionRequest,
+		 * which is useful for implementing OpenAI API proxy servers with @RestController.
+		 * @param key The property name
+		 * @param value The property value
+		 */
+		@JsonAnySetter
+		private void setExtraBodyProperty(String key, Object value) {
+			if (this.extraBody != null) {
+				this.extraBody.put(key, value);
+			}
+		}
+
 		@Override
 		public String toString() {
 			return "TestModelSpecificOptions{" + "specificField='" + this.specificField + '\'' + ", name='" + this.name