diff --git a/common/src/main/kotlin/com/google/ai/client/generativeai/common/Request.kt b/common/src/main/kotlin/com/google/ai/client/generativeai/common/Request.kt
index 4e484266..4bcd4275 100644
--- a/common/src/main/kotlin/com/google/ai/client/generativeai/common/Request.kt
+++ b/common/src/main/kotlin/com/google/ai/client/generativeai/common/Request.kt
@@ -27,12 +27,12 @@ sealed interface Request
 
 @Serializable
 data class GenerateContentRequest(
-  val model: String,
   val contents: List<Content>,
+  val model: String? = null,
   @SerialName("safety_settings") val safetySettings: List<SafetySetting>? = null,
   @SerialName("generation_config") val generationConfig: GenerationConfig? = null,
   val tools: List<Tool>? = null,
 ) : Request
 
 @Serializable
-data class CountTokensRequest(val model: String, val contents: List<Content>) : Request
+data class CountTokensRequest(val contents: List<Content>, val model: String? = null) : Request
diff --git a/common/src/test/java/com/google/ai/client/generativeai/common/util/tests.kt b/common/src/test/java/com/google/ai/client/generativeai/common/util/tests.kt
index d753a9bf..efa2a87e 100644
--- a/common/src/test/java/com/google/ai/client/generativeai/common/util/tests.kt
+++ b/common/src/test/java/com/google/ai/client/generativeai/common/util/tests.kt
@@ -47,7 +47,7 @@ internal fun prepareResponse(response: GenerateContentResponse) =
 internal fun createRequest(vararg text: String): GenerateContentRequest {
   val contents = text.map { Content(parts = listOf(TextPart(it))) }
 
-  return GenerateContentRequest("gemini", contents)
+  return GenerateContentRequest(contents, "gemini")
 }
 
 internal fun createResponse(text: String) = createResponses(text).single()
diff --git a/generativeai/src/main/java/com/google/ai/client/generativeai/GenerativeModel.kt b/generativeai/src/main/java/com/google/ai/client/generativeai/GenerativeModel.kt
index 690f5be4..7c75347f 100644
--- a/generativeai/src/main/java/com/google/ai/client/generativeai/GenerativeModel.kt
+++ b/generativeai/src/main/java/com/google/ai/client/generativeai/GenerativeModel.kt
@@ -173,14 +173,13 @@ internal constructor(
 
   private fun constructRequest(vararg prompt: Content) =
     GenerateContentRequest(
-      modelName,
-      prompt.map { it.toInternal() },
-      safetySettings?.map { it.toInternal() },
-      generationConfig?.toInternal()
+      contents = prompt.map { it.toInternal() },
+      safetySettings = safetySettings?.map { it.toInternal() },
+      generationConfig = generationConfig?.toInternal()
     )
 
   private fun constructCountTokensRequest(vararg prompt: Content) =
-    CountTokensRequest(modelName, prompt.map { it.toInternal() })
+    CountTokensRequest(prompt.map { it.toInternal() })
 
   private fun GenerateContentResponse.validate() = apply {
     if (candidates.isEmpty() && promptFeedback == null) {
diff --git a/generativeai/src/test/java/com/google/ai/client/generativeai/GenerativeModelTests.kt b/generativeai/src/test/java/com/google/ai/client/generativeai/GenerativeModelTests.kt
index bfc0b24c..b23d9c46 100644
--- a/generativeai/src/test/java/com/google/ai/client/generativeai/GenerativeModelTests.kt
+++ b/generativeai/src/test/java/com/google/ai/client/generativeai/GenerativeModelTests.kt
@@ -52,7 +52,6 @@ internal class GenerativeModelTests {
     coEvery {
       mockApiController.generateContent(
         GenerateContentRequest_Common(
-          "gemini-pro-1.0",
           contents = listOf(Content_Common(parts = listOf(TextPart_Common("Why's the sky blue?"))))
         )
       )
@@ -102,7 +101,6 @@ internal class GenerativeModelTests {
     coEvery {
       mockApiController.generateContent(
         GenerateContentRequest_Common(
-          "gemini-pro-1.0",
           contents = listOf(Content_Common(parts = listOf(TextPart_Common("Why's the sky blue?"))))
         )
       )
@@ -117,7 +115,6 @@ internal class GenerativeModelTests {
     coEvery {
       mockApiController.generateContentStream(
         GenerateContentRequest_Common(
-          "gemini-pro-1.0",
           contents = listOf(Content_Common(parts = listOf(TextPart_Common("Why's the sky blue?"))))
         )
       )