feat: RAG - add mode config to RagEngineConfig with Spanner and Serverless (#7016)

* feat: RAG - add mode config to RagEngineConfig with Spanner and Serverless
feat: RAG - deprecate tier from RagEngineConfig
docs: A comment for message `RagManagedDbConfig` is changed
docs: A comment for field `scaled` in message `.google.cloud.aiplatform.v1beta1.RagManagedDbConfig` is changed
docs: A comment for field `basic` in message `.google.cloud.aiplatform.v1beta1.RagManagedDbConfig` is changed
docs: A comment for field `unprovisioned` in message `.google.cloud.aiplatform.v1beta1.RagManagedDbConfig` is changed

PiperOrigin-RevId: 858643621

Source-Link: googleapis/googleapis@87e3579

Source-Link: googleapis/googleapis-gen@ae1d526
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* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
Co-authored-by: miguel <miguelvelezsa@google.com>

Author: gcf-owl-bot[bot]

packages/google-cloud-aiplatform/protos/google/cloud/aiplatform/v1beta1/vertex_rag_data.proto

@@ -1,4 +1,4 @@
-// Copyright 2025 Google LLC
+// Copyright 2026 Google LLC
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -798,7 +798,7 @@ message RagManagedDbConfig {
   // * Latency insensitive workload.
   // * Only using RAG Engine with external vector DBs.
   //
-  // NOTE: This is the default tier if not explicitly chosen.
+  // NOTE: This is the default tier under Spanner mode if not explicitly chosen.
   message Basic {}
 
   // Disables the RAG Engine service and deletes all your data held
@@ -809,20 +809,52 @@ message RagManagedDbConfig {
   // UpdateRagEngineConfig API.
   message Unprovisioned {}
 
+  // Message to configure the Spanner database used by RagManagedDb.
+  message Spanner {
+    // The tier of the RagManagedDb, built on top of Spanner.
+    oneof tier {
+      // Sets the RagManagedDb to the Scaled tier.
+      Scaled scaled = 1;
+
+      // Sets the RagManagedDb to the Basic tier. This is the default tier for
+      // Spanner mode if not explicitly chosen.
+      Basic basic = 2;
+
+      // Sets the RagManagedDb to the Unprovisioned tier.
+      Unprovisioned unprovisioned = 3;
+    }
+  }
+
+  // Message to configure the serverless mode offered by RAG Engine.
+  message Serverless {}
+
   // The tier of the RagManagedDb.
   oneof tier {
     // Sets the RagManagedDb to the Enterprise tier.
     Enterprise enterprise = 1 [deprecated = true];
 
-    // Sets the RagManagedDb to the Scaled tier. This is the default tier
-    // if not explicitly chosen.
-    Scaled scaled = 4;
+    // Deprecated: Use `mode` instead to set the tier under Spanner.
+    // Sets the RagManagedDb to the Scaled tier.
+    Scaled scaled = 4 [deprecated = true];
 
+    // Deprecated: Use `mode` instead to set the tier under Spanner.
     // Sets the RagManagedDb to the Basic tier.
-    Basic basic = 2;
+    Basic basic = 2 [deprecated = true];
 
+    // Deprecated: Use `mode` instead to set the tier under Spanner.
     // Sets the RagManagedDb to the Unprovisioned tier.
-    Unprovisioned unprovisioned = 3;
+    Unprovisioned unprovisioned = 3 [deprecated = true];
+  }
+
+  // The choice of backend for your RagEngine.
+  oneof mode {
+    // Sets the backend to be the serverless mode offered by RAG Engine.
+    Serverless serverless = 5;
+
+    // Sets the RAG Engine backend to be RagManagedDb, built on top of Spanner.
+    //
+    // NOTE: This is the default mode (w/ Basic Tier) if not explicitly chosen.
+    Spanner spanner = 6;
   }
 }
 

packages/google-cloud-aiplatform/protos/google/cloud/aiplatform/v1beta1/vertex_rag_data_service.proto

@@ -1,4 +1,4 @@
-// Copyright 2025 Google LLC
+// Copyright 2026 Google LLC
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.

packages/google-cloud-aiplatform/protos/google/cloud/aiplatform/v1beta1/vertex_rag_service.proto

@@ -1,4 +1,4 @@
-// Copyright 2025 Google LLC
+// Copyright 2026 Google LLC
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.