diff --git a/langchain4j-google-ai-gemini/src/test/java/dev/langchain4j/model/googleai/GoogleAiGeminiChatRequestParametersTest.java b/langchain4j-google-ai-gemini/src/test/java/dev/langchain4j/model/googleai/GoogleAiGeminiChatRequestParametersTest.java
new file mode 100644
index 0000000000..bc9aeb127d
--- /dev/null
+++ b/langchain4j-google-ai-gemini/src/test/java/dev/langchain4j/model/googleai/GoogleAiGeminiChatRequestParametersTest.java
@@ -0,0 +1,146 @@
+package dev.langchain4j.model.googleai;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import dev.langchain4j.model.chat.request.DefaultChatRequestParameters;
+import org.junit.jupiter.api.Test;
+
+class GoogleAiGeminiChatRequestParametersTest {
+
+    @Test
+    void should_build_with_gemini_specific_parameters() {
+        GoogleAiGeminiChatRequestParameters parameters = GoogleAiGeminiChatRequestParameters.builder()
+                .temperature(0.7)
+                .aspectRatio("16:9")
+                .imageSize("2K")
+                .cachedContentName("cachedContents/abc123")
+                .build();
+
+        assertThat(parameters.temperature()).isEqualTo(0.7);
+        assertThat(parameters.aspectRatio()).isEqualTo("16:9");
+        assertThat(parameters.imageSize()).isEqualTo("2K");
+        assertThat(parameters.cachedContentName()).isEqualTo("cachedContents/abc123");
+    }
+
+    @Test
+    void should_default_gemini_specific_parameters_to_null() {
+        assertThat(GoogleAiGeminiChatRequestParameters.EMPTY.aspectRatio()).isNull();
+        assertThat(GoogleAiGeminiChatRequestParameters.EMPTY.imageSize()).isNull();
+        assertThat(GoogleAiGeminiChatRequestParameters.EMPTY.cachedContentName())
+                .isNull();
+    }
+
+    @Test
+    void image_aspect_ratio_should_be_an_alias_for_aspect_ratio() {
+        GoogleAiGeminiChatRequestParameters parameters = GoogleAiGeminiChatRequestParameters.builder()
+                .imageAspectRatio("4:3")
+                .build();
+
+        assertThat(parameters.aspectRatio()).isEqualTo("4:3");
+    }
+
+    @Test
+    void overrideWith_should_override_gemini_specific_parameters() {
+        GoogleAiGeminiChatRequestParameters original = GoogleAiGeminiChatRequestParameters.builder()
+                .aspectRatio("1:1")
+                .imageSize("1K")
+                .cachedContentName("cachedContents/original")
+                .build();
+
+        GoogleAiGeminiChatRequestParameters override = GoogleAiGeminiChatRequestParameters.builder()
+                .aspectRatio("16:9")
+                .cachedContentName("cachedContents/override")
+                .build();
+
+        GoogleAiGeminiChatRequestParameters result = original.overrideWith(override);
+
+        assertThat(result.aspectRatio()).isEqualTo("16:9");
+        assertThat(result.imageSize()).isEqualTo("1K"); // not set in the override, so original value is kept
+        assertThat(result.cachedContentName()).isEqualTo("cachedContents/override");
+    }
+
+    @Test
+    void overrideWith_should_keep_gemini_specific_parameters_when_overriding_with_common_parameters() {
+        GoogleAiGeminiChatRequestParameters original = GoogleAiGeminiChatRequestParameters.builder()
+                .aspectRatio("16:9")
+                .imageSize("2K")
+                .cachedContentName("cachedContents/abc123")
+                .build();
+
+        GoogleAiGeminiChatRequestParameters result = original.overrideWith(
+                DefaultChatRequestParameters.builder().temperature(0.1).build());
+
+        assertThat(result.temperature()).isEqualTo(0.1);
+        assertThat(result.aspectRatio()).isEqualTo("16:9");
+        assertThat(result.imageSize()).isEqualTo("2K");
+        assertThat(result.cachedContentName()).isEqualTo("cachedContents/abc123");
+    }
+
+    @Test
+    void defaultedBy_should_apply_defaults_to_gemini_specific_parameters() {
+        GoogleAiGeminiChatRequestParameters original = GoogleAiGeminiChatRequestParameters.builder()
+                .cachedContentName("cachedContents/original")
+                .build();
+
+        GoogleAiGeminiChatRequestParameters fallback = GoogleAiGeminiChatRequestParameters.builder()
+                .aspectRatio("1:1") // should be defaulted from fallback
+                .imageSize("4K") // should be defaulted from fallback
+                .cachedContentName("cachedContents/fallback") // should be ignored as original has it
+                .build();
+
+        GoogleAiGeminiChatRequestParameters result = original.defaultedBy(fallback);
+
+        assertThat(result.aspectRatio()).isEqualTo("1:1");
+        assertThat(result.imageSize()).isEqualTo("4K");
+        assertThat(result.cachedContentName()).isEqualTo("cachedContents/original");
+    }
+
+    @Test
+    void defaultedBy_should_keep_parameters_when_defaulted_by_common_parameters() {
+        GoogleAiGeminiChatRequestParameters original = GoogleAiGeminiChatRequestParameters.builder()
+                .aspectRatio("16:9")
+                .imageSize("2K")
+                .cachedContentName("cachedContents/abc123")
+                .build();
+
+        GoogleAiGeminiChatRequestParameters result = original.defaultedBy(
+                DefaultChatRequestParameters.builder().temperature(0.1).build());
+
+        assertThat(result.temperature()).isEqualTo(0.1);
+        assertThat(result.aspectRatio()).isEqualTo("16:9");
+        assertThat(result.imageSize()).isEqualTo("2K");
+        assertThat(result.cachedContentName()).isEqualTo("cachedContents/abc123");
+    }
+
+    @Test
+    void equals_and_hashCode() {
+        GoogleAiGeminiChatRequestParameters one = GoogleAiGeminiChatRequestParameters.builder()
+                .temperature(0.7)
+                .aspectRatio("16:9")
+                .imageSize("2K")
+                .cachedContentName("cachedContents/abc123")
+                .build();
+        GoogleAiGeminiChatRequestParameters two = GoogleAiGeminiChatRequestParameters.builder()
+                .temperature(0.7)
+                .aspectRatio("16:9")
+                .imageSize("2K")
+                .cachedContentName("cachedContents/abc123")
+                .build();
+        GoogleAiGeminiChatRequestParameters differentAspectRatio = GoogleAiGeminiChatRequestParameters.builder()
+                .temperature(0.7)
+                .aspectRatio("1:1")
+                .imageSize("2K")
+                .cachedContentName("cachedContents/abc123")
+                .build();
+        GoogleAiGeminiChatRequestParameters differentTemperature = GoogleAiGeminiChatRequestParameters.builder()
+                .temperature(0.3)
+                .aspectRatio("16:9")
+                .imageSize("2K")
+                .cachedContentName("cachedContents/abc123")
+                .build();
+
+        assertThat(one).isEqualTo(two).hasSameHashCodeAs(two);
+        assertThat(one).isNotEqualTo(differentAspectRatio);
+        assertThat(one).isNotEqualTo(differentTemperature);
+    }
+}