diff --git a/.changes/apparatus-bubble-direction-drug.json b/.changes/apparatus-bubble-direction-drug.json
new file mode 100644
index 00000000..801f4f2d
--- /dev/null
+++ b/.changes/apparatus-bubble-direction-drug.json
@@ -0,0 +1 @@
+{"type":"MINOR","changes":["Ensure model names are always prefixed with 'models/'"]}
diff --git a/generativeai/src/main/java/com/google/ai/client/generativeai/internal/api/APIController.kt b/generativeai/src/main/java/com/google/ai/client/generativeai/internal/api/APIController.kt
index 73a8c239..e46016ca 100644
--- a/generativeai/src/main/java/com/google/ai/client/generativeai/internal/api/APIController.kt
+++ b/generativeai/src/main/java/com/google/ai/client/generativeai/internal/api/APIController.kt
@@ -44,7 +44,7 @@ import kotlinx.coroutines.launch
 import kotlinx.serialization.json.Json
 
 // TODO: Should these stay here or be moved elsewhere?
-internal const val DOMAIN = "https://generativelanguage.googleapis.com/v1/models"
+internal const val DOMAIN = "https://generativelanguage.googleapis.com/v1"
 
 internal val JSON = Json {
   ignoreUnknownKeys = true
@@ -63,9 +63,11 @@ internal val JSON = Json {
  */
 internal class APIController(
   private val key: String,
-  private val model: String,
+  model: String,
   httpEngine: HttpClientEngine = OkHttp.create()
 ) {
+  private val model = fullModelName(model)
+
   private val client =
     HttpClient(httpEngine) {
       install(HttpTimeout) {
@@ -106,6 +108,14 @@ internal class APIController(
   }
 }
 
+/**
+ * Ensures the model name provided has a `models/` prefix
+ *
+ * Models must be prepended with the `models/` prefix when communicating with the backend.
+ */
+private fun fullModelName(name: String): String =
+  name.takeIf { it.startsWith("models/") } ?: "models/$name"
+
 /**
  * Makes a POST request to the specified [url] and returns a [Flow] of deserialized response objects
  * of type [R]. The response is expected to be a stream of JSON objects that are parsed in real-time