DEV: Use default LLM model

Author: keegangeorge

config/locales/client.en.yml

@@ -183,7 +183,7 @@ en:
 
       default_llm:
         title: "Default LLM model"
-        description: "The default LLM model to use for all AI features. This will be used if no LLM is specified in the feature configuration or persona."
+        description: "The default LLM model to use for all AI features. This will be used if no LLM is specified in the feature configuration or persona. If no default LLM is specified, the last created LLM will be used."
 
       features:
         short_title: "Features"

config/settings.yml

@@ -109,7 +109,7 @@ discourse_ai:
     default: false
     client: true
     area: "ai-features/ai_helper"
-  ai_helper_model:
+  ai_helper_model:  # Deprecated. TODO(keegan): Remove 2025-09-01
     default: ""
     allow_any: false
     type: enum
@@ -155,7 +155,7 @@ discourse_ai:
       - "context_menu"
       - "image_caption"
     area: "ai-features/ai_helper"
-  ai_helper_image_caption_model:
+  ai_helper_image_caption_model:  # Deprecated. TODO(keegan): Remove 2025-09-01
     default: ""
     type: enum
     enum: "DiscourseAi::Configuration::LlmVisionEnumerator"
@@ -266,7 +266,7 @@ discourse_ai:
     client: true
     validator: "DiscourseAi::Configuration::LlmDependencyValidator"
     area: "ai-features/embeddings"
-  ai_embeddings_semantic_search_hyde_model:
+  ai_embeddings_semantic_search_hyde_model:  # Deprecated. TODO(keegan): Remove 2025-09-01
     default: ""
     type: enum
     allow_any: false
@@ -322,7 +322,7 @@ discourse_ai:
     client: true
     validator: "DiscourseAi::Configuration::LlmDependencyValidator"
     area: "ai-features/summarization"
-  ai_summarization_model:
+  ai_summarization_model: # Deprecated. TODO(keegan): Remove 2025-09-01
     default: ""
     allow_any: false
     type: enum

db/migrate/20250710173803_seed_ai_default_llm_model.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+class SeedAiDefaultLlmModel < ActiveRecord::Migration[7.2]
+  def up
+    return if DB.query_single("SELECT 1 FROM llm_models LIMIT 1").empty?
+
+    last_model_id = DB.query_single("SELECT id FROM llm_models ORDER BY id DESC LIMIT 1").first
+
+    if last_model_id.present?
+      execute "UPDATE site_settings SET value = 'custom:#{last_model_id}' WHERE name = 'ai_default_llm_model' AND (value IS NULL OR value = '');"
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end

db/migrate/20250710180401_copy_ai_summarization_model_to_persona_default.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+class CopyAiSummarizationModelToPersonaDefault < ActiveRecord::Migration[7.2]
+  def up
+    ai_summarization_model =
+      DB.query_single("SELECT value FROM site_settings WHERE name = 'ai_summarization_model'").first
+
+    if ai_summarization_model.present? && ai_summarization_model.start_with?("custom:")
+      # Extract the model ID from the setting value (e.g., "custom:-5" -> "-5")
+      model_id = ai_summarization_model.split(":").last
+
+      # Update the summarization personas (IDs -11 and -12) with the extracted model ID
+      execute(<<~SQL)
+        UPDATE ai_personas
+        SET default_llm_id = #{model_id}
+        WHERE id IN (-11, -12) AND default_llm_id IS NULL
+      SQL
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end

db/migrate/20250710181656_copy_ai_helper_model_to_persona_default.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+class CopyAiHelperModelToPersonaDefault < ActiveRecord::Migration[7.2]
+  def up
+    ai_helper_model =
+      DB.query_single("SELECT value FROM site_settings WHERE name = 'ai_helper_model'").first
+
+    if ai_helper_model.present? && ai_helper_model.start_with?("custom:")
+      # Extract the model ID from the setting value (e.g., "custom:1" -> "1")
+      model_id = ai_helper_model.split(":").last
+
+      # Update the helper personas with the extracted model ID
+      execute(<<~SQL)
+        UPDATE ai_personas
+        SET default_llm_id = #{model_id}
+        WHERE id IN (-18, -19, -20, -21, -22, -23, -24, -25, -26) AND default_llm_id IS NULL
+      SQL
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end

lib/ai_helper/assistant.rb

@@ -312,18 +312,10 @@ def find_ai_helper_model(helper_mode, persona_klass)
 
       # Priorities are:
       #   1. Persona's default LLM
-      #   2. Hidden `ai_helper_model` setting, or `ai_helper_image_caption_model` for image_caption.
-      #   3. Newest LLM config
+      #   2. SiteSetting.ai_default_llm_id (or newest LLM if not set)
       def self.find_ai_helper_model(helper_mode, persona_klass)
-        model_id = persona_klass.default_llm_id
-
-        if !model_id
-          if helper_mode == IMAGE_CAPTION
-            model_id = SiteSetting.ai_helper_image_caption_model&.split(":")&.last
-          else
-            model_id = SiteSetting.ai_helper_model&.split(":")&.last
-          end
-        end
+        model_id =
+          persona_klass.default_llm_id || SiteSetting.ai_default_llm_model&.split(":")&.last # Remove legacy custom provider.
 
         if model_id.present?
           LlmModel.find_by(id: model_id)

lib/embeddings/semantic_search.rb

@@ -210,11 +210,10 @@ def hypothetical_post_from(search_term)
 
       # Priorities are:
       #   1. Persona's default LLM
-      #   2. `ai_embeddings_semantic_search_hyde_model` setting.
+      #   2. SiteSetting.ai_default_llm_id (or newest LLM if not set)
       def find_ai_hyde_model(persona_klass)
         model_id =
-          persona_klass.default_llm_id ||
-            SiteSetting.ai_embeddings_semantic_search_hyde_model&.split(":")&.last
+          persona_klass.default_llm_id || SiteSetting.ai_default_llm_model&.split(":")&.last # Remove legacy custom provider.
 
         return if model_id.blank?
 

lib/summarization.rb

@@ -54,11 +54,10 @@ def chat_channel_summary(channel, time_window_in_hours)
 
       # Priorities are:
       #   1. Persona's default LLM
-      #   2. Hidden `ai_summarization_model` setting
-      #   3. Newest LLM config
+      #   2. SiteSetting.ai_default_llm_id (or newest LLM if not set)
       def find_summarization_model(persona_klass)
         model_id =
-          persona_klass.default_llm_id || SiteSetting.ai_summarization_model&.split(":")&.last # Remove legacy custom provider.
+          persona_klass.default_llm_id || SiteSetting.ai_default_llm_model&.split(":")&.last # Remove legacy custom provider.
 
         if model_id.present?
           LlmModel.find_by(id: model_id)