diff --git a/spring-ai-core/src/main/java/org/springframework/ai/model/function/FunctionCallingOptionsBuilder.java b/spring-ai-core/src/main/java/org/springframework/ai/model/function/FunctionCallingOptionsBuilder.java
index 685618da51..28346f3927 100644
--- a/spring-ai-core/src/main/java/org/springframework/ai/model/function/FunctionCallingOptionsBuilder.java
+++ b/spring-ai-core/src/main/java/org/springframework/ai/model/function/FunctionCallingOptionsBuilder.java
@@ -16,6 +16,7 @@
 package org.springframework.ai.model.function;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
@@ -111,14 +112,18 @@ public FunctionCallingOptionsBuilder withProxyToolCalls(Boolean proxyToolCalls)
 
 	public FunctionCallingOptionsBuilder withToolContext(Map<String, Object> context) {
 		Assert.notNull(context, "Tool context must not be null");
-		this.options.getToolContext().putAll(context);
+		Map<String, Object> newContext = new HashMap<>(this.options.getToolContext());
+		newContext.putAll(context);
+		this.options.setToolContext(newContext);
 		return this;
 	}
 
 	public FunctionCallingOptionsBuilder withToolContext(String key, Object value) {
 		Assert.notNull(key, "Key must not be null");
 		Assert.notNull(value, "Value must not be null");
-		this.options.getToolContext().put(key, value);
+		Map<String, Object> newContext = new HashMap<>(this.options.getToolContext());
+		newContext.put(key, value);
+		this.options.setToolContext(newContext);
 		return this;
 	}
 
@@ -158,22 +163,22 @@ public static FunctionCallingOptionsBuilder builder() {
 
 		@Override
 		public List<FunctionCallback> getFunctionCallbacks() {
-			return this.functionCallbacks;
+			return Collections.unmodifiableList(this.functionCallbacks);
 		}
 
 		public void setFunctionCallbacks(List<FunctionCallback> functionCallbacks) {
 			Assert.notNull(functionCallbacks, "FunctionCallbacks must not be null");
-			this.functionCallbacks = functionCallbacks;
+			this.functionCallbacks = new ArrayList<>(functionCallbacks);
 		}
 
 		@Override
 		public Set<String> getFunctions() {
-			return this.functions;
+			return Collections.unmodifiableSet(this.functions);
 		}
 
 		public void setFunctions(Set<String> functions) {
 			Assert.notNull(functions, "Functions must not be null");
-			this.functions = functions;
+			this.functions = new HashSet<>(functions);
 		}
 
 		@Override
@@ -258,11 +263,12 @@ public void setProxyToolCalls(Boolean proxyToolCalls) {
 		}
 
 		public Map<String, Object> getToolContext() {
-			return context;
+			return Collections.unmodifiableMap(this.context);
 		}
 
 		public void setToolContext(Map<String, Object> context) {
-			this.context = context;
+			Assert.notNull(context, "Context must not be null");
+			this.context = new HashMap<>(context);
 		}
 
 		@Override
@@ -271,14 +277,14 @@ public ChatOptions copy() {
 				.withFrequencyPenalty(this.frequencyPenalty)
 				.withMaxTokens(this.maxTokens)
 				.withPresencePenalty(this.presencePenalty)
-				.withStopSequences(this.stopSequences)
+				.withStopSequences(this.stopSequences != null ? new ArrayList<>(this.stopSequences) : null)
 				.withTemperature(this.temperature)
 				.withTopK(this.topK)
 				.withTopP(this.topP)
-				.withFunctions(this.functions)
-				.withFunctionCallbacks(this.functionCallbacks)
+				.withFunctions(new HashSet<>(this.functions))
+				.withFunctionCallbacks(new ArrayList<>(this.functionCallbacks))
 				.withProxyToolCalls(this.proxyToolCalls)
-				.withToolContext(this.getToolContext())
+				.withToolContext(new HashMap<>(this.getToolContext()))
 				.build();
 		}