FEATURE: configure a default LLM model for all features

assets/javascripts/discourse/components/ai-default-llm-selector.gjs

@@ -0,0 +1,46 @@
+import Component from "@glimmer/component";
+import { tracked } from "@glimmer/tracking";
+import { ajax } from "discourse/lib/ajax";
+import { i18n } from "discourse-i18n";
+import SiteSettingComponent from "admin/components/site-setting";
+import SiteSetting from "admin/models/site-setting";
+
+export default class AiDefaultLlmSelector extends Component {
+  @tracked defaultLlmSetting = null;
+
+  constructor() {
+    super(...arguments);
+    this.#loadDefaultLlmSetting();
+  }
+
+  async #loadDefaultLlmSetting() {
+    const { site_settings } = await ajax("/admin/config/site_settings.json", {
+      data: {
+        plugin: "discourse-ai",
+        category: "discourse_ai",
+      },
+    });
+
+    const defaultLlmSetting = site_settings.find(
+      (setting) => setting.setting === "ai_default_llm_model"
+    );
+
+    this.defaultLlmSetting = SiteSetting.create(defaultLlmSetting);
+  }
+
+  <template>
+    <div class="ai-configure-default-llm">
+      <div class="ai-configure-default-llm__header">
+        <h3>{{i18n "discourse_ai.default_llm.title"}}</h3>
+        <p>{{i18n "discourse_ai.default_llm.description"}}</p>
+      </div>
+
+      {{#if this.defaultLlmSetting}}
+        <SiteSettingComponent
+          @setting={{this.defaultLlmSetting}}
+          class="ai-configure-default-llm__setting"
+        />
+      {{/if}}
+    </div>
+  </template>
+}

assets/javascripts/discourse/components/ai-features.gjs

@@ -9,6 +9,7 @@ import DPageSubheader from "discourse/components/d-page-subheader";
 import DSelect from "discourse/components/d-select";
 import FilterInput from "discourse/components/filter-input";
 import { i18n } from "discourse-i18n";
+import AiDefaultLlmSelector from "./ai-default-llm-selector";
 import AiFeaturesList from "./ai-features-list";
 
 const ALL = "all";
@@ -202,6 +203,8 @@ export default class AiFeatures extends Component {
         />
       </div>
 
+      <AiDefaultLlmSelector />
+
       {{#if this.filteredFeatures.length}}
         <AiFeaturesList @modules={{this.filteredFeatures}} />
       {{else}}

assets/javascripts/discourse/components/ai-llms-list-editor.gjs

@@ -9,6 +9,7 @@ import I18n, { i18n } from "discourse-i18n";
 import AdminSectionLandingItem from "admin/components/admin-section-landing-item";
 import AdminSectionLandingWrapper from "admin/components/admin-section-landing-wrapper";
 import DTooltip from "float-kit/components/d-tooltip";
+import AiDefaultLlmSelector from "./ai-default-llm-selector";
 import AiLlmEditor from "./ai-llm-editor";
 
 function isPreseeded(llm) {
@@ -137,6 +138,9 @@ export default class AiLlmsListEditor extends Component {
           }}
           @learnMoreUrl="https://meta.discourse.org/t/discourse-ai-large-language-model-llm-settings-page/319903"
         />
+
+        <AiDefaultLlmSelector />
+
         {{#if this.hasLlmElements}}
           <section class="ai-llms-list-editor__configured">
             <DPageSubheader

assets/stylesheets/common/ai-features.scss

@@ -158,3 +158,51 @@
 .ai-expanded-list__toggle-button {
   padding: 0;
 }
+
+.ai-configure-default-llm {
+  display: flex;
+  align-items: center;
+  gap: var(--space-2);
+  background: var(--primary-very-low);
+  padding: 1rem;
+  margin-block: 1rem;
+  border-radius: var(--d-border-radius);
+
+  &__header {
+    flex: 3;
+  }
+
+  &__setting {
+    flex: 2;
+    display: flex;
+    gap: var(--space-2);
+    align-items: center;
+    justify-content: center;
+
+    .setting-controls__undo {
+      display: none;
+    }
+  }
+
+  h3 {
+    color: var(--primary);
+    font-size: var(--font-0);
+    margin-bottom: 0;
+  }
+
+  p {
+    margin-top: 0;
+    font-size: var(--font-down-1);
+    color: var(--primary-high-or-secondary-low);
+  }
+
+  .select-kit,
+  .btn {
+    font-size: var(--font-down-1);
+  }
+
+  .setting-label,
+  .desc {
+    display: none;
+  }
+}

config/locales/client.en.yml

@@ -181,6 +181,10 @@ en:
     discourse_ai:
       title: "AI"
 
+      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. If no default LLM is specified, the last created LLM will be used."
+
       features:
         short_title: "Features"
         description: "These are the AI features available to visitors on your site. These can be configured to use specific personas and LLMs, and can be access controlled by groups."

config/locales/server.en.yml

@@ -25,6 +25,7 @@ en:
         description: "Periodic report based on a large language model"
   site_settings:
     discourse_ai_enabled: "Enable the discourse AI plugin."
+    ai_default_llm_model: "The default LLM model to use for all AI features"
     ai_artifact_security: "The AI artifact system generates IFRAMEs with runnable code. Strict mode forces an extra click to run code. Lax mode runs code immediately. Hybrid mode allows user to supply data-ai-artifact-autorun to show right away. Disabled mode disables the artifact system."
     ai_toxicity_enabled: "Enable the toxicity module."
     ai_toxicity_inference_service_api_endpoint: "URL where the API is running for the toxicity module"

config/settings.yml

@@ -11,6 +11,12 @@ discourse_ai:
       - "lax"
       - "hybrid"
       - "strict"
+  ai_default_llm_model:
+    default: ""
+    type: enum
+    allow_any: false
+    enum: "DiscourseAi::Configuration::LlmEnumerator"
+    validator: "DiscourseAi::Configuration::SimpleLlmValidator"
 
   ai_sentiment_enabled:
     default: false
@@ -103,7 +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
@@ -149,7 +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"
@@ -260,7 +266,8 @@ 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
+    hidden: true
     default: ""
     type: enum
     allow_any: false
@@ -316,7 +323,7 @@ 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

db/migrate/20250710215720_copy_hyde_model_to_persona.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+class CopyHydeModelToPersona < ActiveRecord::Migration[7.2]
+  def up
+    hyde_model =
+      DB.query_single("SELECT value FROM site_settings WHERE name = 'ai_embeddings_semantic_search_hyde_model'").first
+
+    if hyde_model.present? && hyde_model.start_with?("custom:")
+      # Extract the model ID from the setting value (e.g., "custom:1" -> "1")
+      model_id = hyde_model.split(":").last
+
+      # Update the hyde persona with the extracted model ID
+      execute(<<~SQL)
+        UPDATE ai_personas
+        SET default_llm_id = #{model_id}
+        WHERE id IN (-32) AND default_llm_id IS NULL
+      SQL
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end

lib/ai_helper/assistant.rb

@@ -312,22 +312,21 @@ 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)
         else
+          last_model_id = LlmModel.last&.id
+
+          # SiteSetting.ai_default_llm_model shouldn't be empty, but if it is, we set it to the last model.
+          if last_model_id.present? && SiteSetting.ai_default_llm_model.empty?
+            SiteSetting.set_and_log("ai_default_llm_model", "custom:#{last_model_id}", Discourse.system_user) # Remove legacy custom provider.
+          end
+
           LlmModel.last
         end
       end

lib/ai_helper/painter.rb

@@ -66,7 +66,7 @@ def diffusion_prompt(text, user)
             messages: [{ type: :user, content: text, id: user.username }],
           )
 
-        DiscourseAi::Completions::Llm.proxy(SiteSetting.ai_helper_model).generate(
+        DiscourseAi::Completions::Llm.proxy(SiteSetting.ai_default_llm_model).generate(
           prompt,
           user: user,
           feature_name: "illustrate_post",

lib/configuration/llm_dependency_validator.rb

@@ -10,7 +10,8 @@ def initialize(opts = {})
       def valid_value?(val)
         return true if val == "f"
 
-        if @opts[:name] == :ai_summarization_enabled || @opts[:name] == :ai_helper_enabled
+        if @opts[:name] == :ai_summarization_enabled || @opts[:name] == :ai_helper_enabled ||
+             @opts[:name] == :ai_embeddings_semantic_search_enabled
           has_llms = LlmModel.count > 0
           @no_llms_configured = !has_llms
           has_llms

lib/configuration/simple_llm_validator.rb

@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+module DiscourseAi
+  module Configuration
+    class SimpleLlmValidator
+      def initialize(opts = {})
+        @opts = opts
+      end
+
+      def valid_value?(val)
+        return true if val == ""
+
+        run_test(val).tap { |result| @unreachable = result }
+      rescue StandardError => e
+        raise e if Rails.env.test?
+        @unreachable = true
+        true
+      end
+
+      def run_test(val)
+        if Rails.env.test?
+          # In test mode, we assume the model is reachable.
+          return true
+        end
+
+        DiscourseAi::Completions::Llm
+          .proxy(val)
+          .generate("How much is 1 + 1?", user: nil, feature_name: "llm_validator")
+          .present?
+      end
+
+      def error_message
+        return unless @unreachable
+
+        I18n.t("discourse_ai.llm.configuration.model_unreachable")
+      end
+    end
+  end
+end