From ca32a1996fd92c1612f95cfe74ba94756e5818b9 Mon Sep 17 00:00:00 2001
From: Chad Palmer <chadpalmer@gmail.com>
Date: Tue, 22 Sep 2026 21:38:13 +0000
Subject: [PATCH] add-default-model-admin-setting - added new admin model and
 reasoning effort default value feature for new chats.

---
 application/single_app/config.py              |  2 +-
 application/single_app/functions_settings.py  |  2 +
 application/single_app/route_backend_chats.py | 57 +++++++++++++-
 .../route_frontend_admin_settings.py          | 19 +++++
 .../single_app/route_frontend_chats.py        | 24 +++++-
 .../static/js/chat/chat-conversations.js      | 14 +++-
 .../static/js/chat/chat-messages.js           | 41 +++++++++-
 .../static/js/chat/chat-model-selector.js     | 55 ++++++++++++++
 .../single_app/static/js/chat/chat-onload.js  |  9 ++-
 .../static/js/chat/chat-reasoning.js          | 16 ++++
 .../static/js/chat/chat-searchable-select.js  |  5 +-
 .../admin/_panes/model-endpoints.html         | 41 +++++++++-
 application/single_app/templates/chats.html   |  7 ++
 docs/_data/app_surface.yml                    |  4 +-
 docs/_data/features.yml                       |  1 +
 docs/admin/ai-models.md                       |  4 +-
 docs/explanation/release_notes.md             | 18 +++++
 ...elector_initial_multiendpoint_bootstrap.py | 75 +++++++++++++++++--
 ...est_chat_template_json_bootstrap_safety.py |  9 ++-
 .../test_default_model_selection_fallback.py  | 75 +++++++++++++++++--
 .../admin_settings_field_baseline.json        |  2 +
 21 files changed, 451 insertions(+), 29 deletions(-)

diff --git a/application/single_app/config.py b/application/single_app/config.py
index 892520372..1bf69d8d7 100644
--- a/application/single_app/config.py
+++ b/application/single_app/config.py
@@ -98,7 +98,7 @@
 EXECUTOR_TYPE = 'thread'
 EXECUTOR_MAX_WORKERS = 30
 SESSION_TYPE = 'filesystem'
-VERSION = "0.261.039"
+VERSION = "0.261.044"
 IS_DEVELOPMENT = is_development_env_enabled()
 
 # Opt-out for deployments where App Service Easy Auth is active but the platform
diff --git a/application/single_app/functions_settings.py b/application/single_app/functions_settings.py
index 0782c1f45..361cefc20 100644
--- a/application/single_app/functions_settings.py
+++ b/application/single_app/functions_settings.py
@@ -1503,11 +1503,13 @@ def get_settings(use_cosmos=False, include_source=False):
         'model_endpoint_identity_header_name': DEFAULT_MODEL_ENDPOINT_IDENTITY_HEADER_NAME,
         'model_endpoint_identity_header_value_type': DEFAULT_MODEL_ENDPOINT_IDENTITY_HEADER_VALUE_TYPE,
         'model_endpoint_identity_header_hmac_secret': secrets.token_urlsafe(48),
+        'enable_default_model_for_new_conversations': False,
         'default_model_selection': {
             'endpoint_id': '',
             'model_id': '',
             'provider': ''
         },
+        'default_reasoning_effort': '',
         'multi_endpoint_migrated_at': None,
         'multi_endpoint_migration_notice': {
             'enabled': False,
diff --git a/application/single_app/route_backend_chats.py b/application/single_app/route_backend_chats.py
index 2206e7c04..125e2445c 100644
--- a/application/single_app/route_backend_chats.py
+++ b/application/single_app/route_backend_chats.py
@@ -478,6 +478,42 @@ def _resolve_reasoning_effort_for_model(reasoning_effort, model_name, provider=N
     return resolved_reasoning_effort
 
 
+def _normalize_default_reasoning_effort(reasoning_effort):
+    normalized_reasoning_effort = str(reasoning_effort or '').strip().lower()
+    if normalized_reasoning_effort in ('', 'none', 'minimal', 'low', 'medium', 'high'):
+        return normalized_reasoning_effort
+    return ''
+
+
+def _apply_admin_new_conversation_model_defaults(settings, data, conversation_id, request_agent_info, *, is_retry=False):
+    """Apply admin model defaults when a normal chat request starts a new conversation."""
+    if (
+        conversation_id
+        or is_retry
+        or _has_chat_agent_selection(request_agent_info)
+        or not settings.get('enable_multi_model_endpoints', False)
+        or not settings.get('enable_default_model_for_new_conversations', False)
+    ):
+        return False
+
+    default_selection = settings.get('default_model_selection', {}) or {}
+    default_endpoint_id = str(default_selection.get('endpoint_id') or '').strip()
+    default_model_id = str(default_selection.get('model_id') or '').strip()
+    default_provider = str(default_selection.get('provider') or '').strip().lower()
+    if not (default_endpoint_id and default_model_id):
+        return False
+
+    data['model_endpoint_id'] = default_endpoint_id
+    data['model_id'] = default_model_id
+    data['model_provider'] = default_provider
+    data['model_deployment'] = ''
+    default_reasoning_effort = _normalize_default_reasoning_effort(settings.get('default_reasoning_effort'))
+    if default_reasoning_effort:
+        data['reasoning_effort'] = None if default_reasoning_effort == 'none' else default_reasoning_effort
+    data['_admin_default_model_applied'] = True
+    return True
+
+
 def _apply_response_length_for_model(api_params, response_length, model_name, provider=None, response_length_parameter=None):
     normalized_response_length = normalize_model_response_length(response_length)
     if not normalized_response_length:
@@ -14453,7 +14489,7 @@ def resolve_streaming_multi_endpoint_gpt_config(settings, data, user_id, active_
     if requested_endpoint_id:
         if not (requested_model_id or requested_deployment):
             raise ValueError('Selected model information is incomplete for the streaming request.')
-        selection_source = 'request'
+        selection_source = 'default' if data.get('_admin_default_model_applied') else 'request'
     elif allow_default_selection:
         default_selection = settings.get('default_model_selection', {}) or {}
         default_endpoint_id = str(default_selection.get('endpoint_id') or '').strip()
@@ -16800,6 +16836,14 @@ def chat_api():
             conversation_id = getattr(g, 'conversation_id', None) or data.get('conversation_id')
             if conversation_id is not None:
                 conversation_id = str(conversation_id).strip() or None
+            request_is_retry = bool(data.get('retry_user_message_id') or data.get('edited_user_message_id'))
+            _apply_admin_new_conversation_model_defaults(
+                settings,
+                data,
+                conversation_id,
+                request_agent_info,
+                is_retry=request_is_retry,
+            )
             hybrid_search_enabled = data.get('hybrid_search')
             web_search_enabled = data.get('web_search_enabled')
             url_access_enabled = data.get('url_access_enabled')
@@ -16899,7 +16943,7 @@ def result_requires_message_reload(result: Any) -> bool:
             retry_user_message_id = data.get('retry_user_message_id') or data.get('edited_user_message_id')
             retry_thread_id = data.get('retry_thread_id')
             retry_thread_attempt = data.get('retry_thread_attempt')
-            is_retry = bool(retry_user_message_id)
+            is_retry = request_is_retry
             is_edit = bool(data.get('edited_user_message_id'))
 
             if is_retry:
@@ -17869,6 +17913,7 @@ def result_requires_message_reload(result: Any) -> bool:
                     'model_icon': gpt_model_icon,
                     'response_length': gpt_response_length,
                     'reasoning_effort': reasoning_effort if reasoning_effort and reasoning_effort != 'none' else None,
+                    'admin_default_applied': bool(data.get('_admin_default_model_applied')),
                     'streaming': 'Disabled'
                 }
 
@@ -21196,6 +21241,13 @@ def chat_stream_api():
         data['active_group_id'] = initial_scope_context['active_group_id']
         data['active_public_workspace_ids'] = list(initial_scope_context['active_public_workspace_ids'])
         data['active_public_workspace_id'] = initial_scope_context['active_public_workspace_id']
+        _apply_admin_new_conversation_model_defaults(
+            settings,
+            data,
+            None if is_new_stream_conversation else finalized_conversation_id,
+            data.get('agent_info'),
+            is_retry=is_retry,
+        )
         stream_session = CHAT_STREAM_REGISTRY.start_session(user_id, finalized_conversation_id)
 
         request_message = (data.get('message') or '').strip()
@@ -22453,6 +22505,7 @@ def collect_stream_response_conversation_metadata():
                         'model_icon': gpt_model_icon,
                         'response_length': gpt_response_length,
                         'reasoning_effort': reasoning_effort if reasoning_effort and reasoning_effort != 'none' else None,
+                        'admin_default_applied': bool(data.get('_admin_default_model_applied')),
                         'streaming': 'Enabled'
                     }
 
diff --git a/application/single_app/route_frontend_admin_settings.py b/application/single_app/route_frontend_admin_settings.py
index 9c8412517..09d6c76b1 100644
--- a/application/single_app/route_frontend_admin_settings.py
+++ b/application/single_app/route_frontend_admin_settings.py
@@ -560,6 +560,10 @@ def admin_settings():
                 'model_id': '',
                 'provider': ''
             }
+        if 'enable_default_model_for_new_conversations' not in settings:
+            settings['enable_default_model_for_new_conversations'] = False
+        if 'default_reasoning_effort' not in settings:
+            settings['default_reasoning_effort'] = ''
         if 'metadata_extraction_model_selection' not in settings or not isinstance(settings.get('metadata_extraction_model_selection'), dict):
             settings['metadata_extraction_model_selection'] = {
                 'endpoint_id': '',
@@ -1868,6 +1872,19 @@ def parse_admin_int(raw_value, fallback_value, field_name="unknown", hard_defaul
                     'provider': ''
                 }
 
+            enable_default_model_for_new_conversations = (
+                enable_multi_model_endpoints
+                and form_data.get('enable_default_model_for_new_conversations') == 'on'
+            )
+            default_reasoning_effort = (
+                form_data.get('default_reasoning_effort', '').strip().lower()
+            )
+            if default_reasoning_effort not in ('', 'none', 'minimal', 'low', 'medium', 'high'):
+                flash('Default reasoning effort is not valid. Please select a supported value.', 'warning')
+                default_reasoning_effort = ''
+            if not enable_default_model_for_new_conversations:
+                default_reasoning_effort = ''
+
             metadata_selection_json = form_data.get('metadata_extraction_model_selection_json', '{}')
             parsed_metadata_model_selection = {}
             try:
@@ -2520,7 +2537,9 @@ def is_valid_url(url):
                 'model_endpoint_identity_header_name': model_endpoint_identity_header_name,
                 'model_endpoint_identity_header_value_type': model_endpoint_identity_header_value_type,
                 'model_endpoint_identity_header_hmac_secret': settings.get('model_endpoint_identity_header_hmac_secret', ''),
+                'enable_default_model_for_new_conversations': enable_default_model_for_new_conversations,
                 'default_model_selection': normalized_default_model_selection,
+                'default_reasoning_effort': default_reasoning_effort,
                 'multi_endpoint_migrated_at': migrated_at,
                 'multi_endpoint_migration_notice': migration_notice,
                 'azure_apim_gpt_endpoint': form_data.get('azure_apim_gpt_endpoint', '').strip(),
diff --git a/application/single_app/route_frontend_chats.py b/application/single_app/route_frontend_chats.py
index f81ef71c4..6b4d4a956 100644
--- a/application/single_app/route_frontend_chats.py
+++ b/application/single_app/route_frontend_chats.py
@@ -496,7 +496,14 @@ def _filter_chat_model_endpoints_by_governance(user_id, endpoints, feature_key):
     return allowed_endpoints
 
 
-def _build_initial_chat_model_selection(*, chat_model_options, preferred_model_id=None, preferred_model_deployment=None):
+def _build_initial_chat_model_selection(
+    *,
+    chat_model_options,
+    preferred_model_id=None,
+    preferred_model_deployment=None,
+    default_model_selection=None,
+    use_admin_default=False,
+):
     scope_order = {
         'global': 0,
         'personal': 1,
@@ -574,6 +581,16 @@ def sort_key(option):
     normalized_preferred_model_id = _normalize_chat_model_value(preferred_model_id)
     normalized_preferred_model_deployment = _normalize_chat_model_value(preferred_model_deployment)
 
+    if use_admin_default and isinstance(default_model_selection, dict):
+        default_endpoint_id = _normalize_chat_model_value(default_model_selection.get('endpoint_id'))
+        default_model_id = _normalize_chat_model_value(default_model_selection.get('model_id'))
+        if default_endpoint_id and default_model_id:
+            for option in sorted_options:
+                endpoint_id = _normalize_chat_model_value(option.get('endpoint_id'))
+                model_id = _normalize_chat_model_value(option.get('model_id'))
+                if endpoint_id == default_endpoint_id and model_id == default_model_id:
+                    return serialize_option(option)
+
     if normalized_preferred_model_id:
         for option in sorted_options:
             selection_key = _normalize_chat_model_value(option.get('selection_key'))
@@ -967,6 +984,11 @@ def chats():
             chat_model_options=chat_model_options,
             preferred_model_id=user_settings_dict.get('preferredModelId'),
             preferred_model_deployment=user_settings_dict.get('preferredModelDeployment'),
+            default_model_selection=settings.get('default_model_selection', {}),
+            use_admin_default=bool(
+                enable_multi_model_endpoints
+                and settings.get('enable_default_model_for_new_conversations', False)
+            ),
         )
 
         return render_template(
diff --git a/application/single_app/static/js/chat/chat-conversations.js b/application/single_app/static/js/chat/chat-conversations.js
index 361adbee1..bb8be2edf 100644
--- a/application/single_app/static/js/chat/chat-conversations.js
+++ b/application/single_app/static/js/chat/chat-conversations.js
@@ -97,9 +97,14 @@ async function refreshModelSelection() {
   try {
     const settings = await loadUserSettings();
     const modelSelectorModule = await import('./chat-model-selector.js');
+    const useAdminDefault = Boolean(
+      window.adminNewConversationDefaultsActive
+      && window.appSettings?.enable_default_model_for_new_conversations
+      && window.initialChatModelSelection?.selection_key
+    );
     await modelSelectorModule.populateModelDropdown({
-      preferredModelId: settings?.preferredModelId,
-      preferredModelDeployment: settings?.preferredModelDeployment,
+      preferredModelId: useAdminDefault ? window.initialChatModelSelection.selection_key : settings?.preferredModelId,
+      preferredModelDeployment: useAdminDefault ? null : settings?.preferredModelDeployment,
       preserveCurrentSelection: false,
     });
   } catch (error) {
@@ -1517,6 +1522,7 @@ export function addConversationToList(conversationId, title = null, classificati
 export async function selectConversation(conversationId) {
   currentConversationId = conversationId;
   window.currentConversationId = conversationId;
+  window.adminNewConversationDefaultsActive = false;
   notifyConversationContextChanged("select", conversationId);
 
   const convoItem = document.querySelector(`.conversation-item[data-conversation-id="${conversationId}"]`);
@@ -2219,6 +2225,10 @@ export async function createNewConversation(callback, options = {}) {
       }
 
       currentConversationId = data.conversation_id;
+      window.adminNewConversationDefaultsActive = Boolean(
+        window.appSettings?.enable_multi_model_endpoints
+        && window.appSettings?.enable_default_model_for_new_conversations
+      );
       // Reset scope lock for new conversation
       resetScopeLock({ preserveSelections });
       // Add to list (pass empty classifications for new convo)
diff --git a/application/single_app/static/js/chat/chat-messages.js b/application/single_app/static/js/chat/chat-messages.js
index 61b006015..1d2091c75 100644
--- a/application/single_app/static/js/chat/chat-messages.js
+++ b/application/single_app/static/js/chat/chat-messages.js
@@ -25,6 +25,10 @@ import { autoplayTTSIfEnabled, isTTSAutoplayEnabled, playTTS } from "./chat-tts.
 import { saveUserSetting } from "./chat-layout.js";
 import { sendMessageWithStreaming } from "./chat-streaming.js";
 import { getCurrentReasoningEffort, isReasoningEffortEnabled } from './chat-reasoning.js';
+import {
+  restoreAdminDefaultModelSelection,
+  restoreModelSelectionFromConversationMetadata,
+} from './chat-model-selector.js';
 import { areAgentsEnabled } from './chat-agents.js';
 import { createThoughtsToggleHtml, attachThoughtsToggleListener } from './chat-thoughts.js';
 import { destroyInlineCharts, extractInlineChartBlocks, hydrateInlineCharts, injectInlineChartHtml, restoreInlineChartTokens } from './chat-inline-charts.js';
@@ -2128,6 +2132,21 @@ export function groupGeneratedImageProposalMessages(messages = []) {
   return groupedMessages;
 }
 
+function getLastConversationModelSelection(messages = []) {
+  if (!Array.isArray(messages)) {
+    return null;
+  }
+
+  for (let index = messages.length - 1; index >= 0; index -= 1) {
+    const modelSelection = messages[index]?.metadata?.model_selection;
+    if (modelSelection && typeof modelSelection === 'object') {
+      return modelSelection;
+    }
+  }
+
+  return null;
+}
+
 export function loadMessages(conversationId) {
     window.SimpleChatM365PendingActions?.setConversation(conversationId);
   // Clear search highlights when loading a different conversation
@@ -2159,6 +2178,19 @@ export function loadMessages(conversationId) {
       console.log(`--- Loading messages for ${conversationId} ---`);
       updateConversationTaskDocumentsFromMessages(Array.isArray(data.messages) ? data.messages : [], conversationId);
       updateComparisonChatUploadCatalog(Array.isArray(data.messages) ? data.messages : []);
+      const lastModelSelection = getLastConversationModelSelection(data.messages);
+      if (lastModelSelection) {
+        window.adminNewConversationDefaultsActive = false;
+        restoreModelSelectionFromConversationMetadata(lastModelSelection);
+      } else if ((Array.isArray(data.messages) ? data.messages : []).length === 0) {
+        window.adminNewConversationDefaultsActive = Boolean(
+          window.appSettings?.enable_multi_model_endpoints
+          && window.appSettings?.enable_default_model_for_new_conversations
+        );
+        restoreAdminDefaultModelSelection();
+      } else {
+        window.adminNewConversationDefaultsActive = false;
+      }
       const generatedImageProposalMessages = groupGeneratedImageProposalMessages(data.messages);
       const assistantMessageIds = new Set(
         (Array.isArray(data.messages) ? data.messages : [])
@@ -8666,7 +8698,13 @@ document.addEventListener('DOMContentLoaded', function() {
 
 // Save the selected model when it changes
 if (modelSelect) {
-  modelSelect.addEventListener("change", function() {
+  modelSelect.addEventListener("change", function(event) {
+    const userInitiated = event.isTrusted || event.detail?.userInitiated === true;
+    if (userInitiated) {
+      window.adminNewConversationDefaultsActive = false;
+    } else {
+      return;
+    }
     const selectedModel = modelSelect.value;
     if (window.appSettings?.enable_multi_model_endpoints) {
       const selectedOption = modelSelect.options[modelSelect.selectedIndex];
@@ -8677,6 +8715,7 @@ if (modelSelect) {
       console.log(`Saving preferred model deployment: ${selectedModel}`);
       saveUserSetting({ preferredModelDeployment: selectedModel });
     }
+
   });
 }
 
diff --git a/application/single_app/static/js/chat/chat-model-selector.js b/application/single_app/static/js/chat/chat-model-selector.js
index b339aa5a5..53df31902 100644
--- a/application/single_app/static/js/chat/chat-model-selector.js
+++ b/application/single_app/static/js/chat/chat-model-selector.js
@@ -610,4 +610,59 @@ export function refreshModelSelector() {
     }
 
     modelSelectorController?.refresh();
+}
+
+function findModelOptionForMetadata(modelSelection = {}) {
+    if (!modelSelect || !modelSelection || typeof modelSelection !== 'object') {
+        return null;
+    }
+
+    const endpointId = String(modelSelection.model_endpoint_id || modelSelection.endpoint_id || '').trim();
+    const modelId = String(modelSelection.model_id || '').trim();
+    const selectedModel = String(modelSelection.selected_model || modelSelection.request_model || '').trim();
+    const frontendModel = String(modelSelection.frontend_requested_model || modelSelection.deployment_name || '').trim();
+    const options = Array.from(modelSelect.options).filter(option => !option.disabled);
+
+    if (endpointId && modelId) {
+        const endpointMatch = options.find(option => (
+            option.dataset.endpointId === endpointId
+            && option.dataset.modelId === modelId
+        ));
+        if (endpointMatch) {
+            return endpointMatch;
+        }
+    }
+
+    const modelNames = [frontendModel, selectedModel].filter(Boolean);
+    return options.find(option => modelNames.some(modelName => (
+        option.dataset.requestModel === modelName
+        || option.dataset.deploymentName === modelName
+        || option.value === modelName
+    ))) || null;
+}
+
+export function restoreModelSelectionFromConversationMetadata(modelSelection = {}) {
+    const matchingOption = findModelOptionForMetadata(modelSelection);
+    if (!matchingOption || !modelSelect) {
+        return false;
+    }
+
+    modelSelect.value = matchingOption.value;
+    matchingOption.selected = true;
+    modelSelectorController?.refresh();
+    modelSelect.dispatchEvent(new CustomEvent('change', {
+        bubbles: true,
+        detail: { conversationRestore: true }
+    }));
+    return true;
+}
+
+export function restoreAdminDefaultModelSelection() {
+    if (!window.appSettings?.enable_default_model_for_new_conversations) {
+        return false;
+    }
+
+    return restoreModelSelectionFromConversationMetadata(
+        window.initialChatModelSelection || window.appSettings.default_model_selection || {}
+    );
 }
\ No newline at end of file
diff --git a/application/single_app/static/js/chat/chat-onload.js b/application/single_app/static/js/chat/chat-onload.js
index 34036bc19..b4985cb8c 100644
--- a/application/single_app/static/js/chat/chat-onload.js
+++ b/application/single_app/static/js/chat/chat-onload.js
@@ -157,8 +157,13 @@ window.addEventListener('DOMContentLoaded', async () => {
   try {
       const userSettings = await userSettingsPromise;
       
-                const preferredModelId = userSettings?.preferredModelId;
-                const preferredModelDeployment = userSettings?.preferredModelDeployment;
+                let preferredModelId = userSettings?.preferredModelId;
+                let preferredModelDeployment = userSettings?.preferredModelDeployment;
+
+                if (window.appSettings?.enable_default_model_for_new_conversations && window.initialChatModelSelection?.selection_key) {
+                    preferredModelId = window.initialChatModelSelection.selection_key;
+                    preferredModelDeployment = null;
+                }
 
             initializeModelSelector();
             await populateModelDropdown({
diff --git a/application/single_app/static/js/chat/chat-reasoning.js b/application/single_app/static/js/chat/chat-reasoning.js
index 545aa6cf8..bda56640f 100644
--- a/application/single_app/static/js/chat/chat-reasoning.js
+++ b/application/single_app/static/js/chat/chat-reasoning.js
@@ -4,6 +4,16 @@ import { showToast } from './chat-toast.js';
 
 let reasoningEffortSettings = {}; // Per-model settings: {modelName: 'low', ...}
 
+function getAdminDefaultReasoningEffort() {
+    if (!window.appSettings?.enable_default_model_for_new_conversations) {
+        return '';
+    }
+    if (window.adminNewConversationDefaultsActive === false) {
+        return '';
+    }
+    return String(window.appSettings?.default_reasoning_effort || '').trim().toLowerCase();
+}
+
 function setTooltipText(element, text, options = {}) {
     if (!element) {
         return;
@@ -210,11 +220,16 @@ export function getCurrentModelReasoningEffort() {
     
     const supportedLevels = getModelSupportedLevels(modelName);
     const savedEffort = reasoningEffortSettings[modelName];
+    const adminDefaultEffort = getAdminDefaultReasoningEffort();
     
     // If gpt-5-pro, always return high
     if (modelName.toLowerCase().includes('gpt-5-pro')) {
         return 'high';
     }
+
+    if (adminDefaultEffort && supportedLevels.includes(adminDefaultEffort)) {
+        return adminDefaultEffort;
+    }
     
     // If saved effort exists and is supported, use it
     if (savedEffort && supportedLevels.includes(savedEffort)) {
@@ -404,6 +419,7 @@ function selectReasoningLevel(level, modelName) {
  * @param {string} effort - The effort level
  */
 export function saveReasoningEffort(modelName, effort) {
+    window.adminNewConversationDefaultsActive = false;
     reasoningEffortSettings[modelName] = effort;
     saveUserSetting({ reasoningEffortSettings });
 }
diff --git a/application/single_app/static/js/chat/chat-searchable-select.js b/application/single_app/static/js/chat/chat-searchable-select.js
index 07a96e3b8..ba3f467d6 100644
--- a/application/single_app/static/js/chat/chat-searchable-select.js
+++ b/application/single_app/static/js/chat/chat-searchable-select.js
@@ -496,7 +496,10 @@ export function createSearchableSingleSelect({
 
         selectEl.selectedIndex = normalizedIndex;
         renderOptions();
-        selectEl.dispatchEvent(new Event('change', { bubbles: true }));
+        selectEl.dispatchEvent(new CustomEvent('change', {
+            bubbles: true,
+            detail: { userInitiated: true }
+        }));
 
         try {
             bootstrap.Dropdown.getOrCreateInstance(buttonEl, resolvedDropdownConfig).hide();
diff --git a/application/single_app/templates/admin/_panes/model-endpoints.html b/application/single_app/templates/admin/_panes/model-endpoints.html
index ca2accd85..03a29cb44 100644
--- a/application/single_app/templates/admin/_panes/model-endpoints.html
+++ b/application/single_app/templates/admin/_panes/model-endpoints.html
@@ -238,10 +238,45 @@ <h6 class="mb-1"><i class="bi bi-fingerprint me-2"></i>Model Endpoint Identity H
                     </div>
 
                     <div id="default-model-selection-wrapper" class="mt-3">
-                        <label for="default-model-selection" class="form-label">Default model for fallbacks</label>
-                        <select class="form-select" id="default-model-selection" aria-label="Default model for fallback selection"></select>
+                        <label for="default-model-selection" class="form-label">Default model for fallbacks and new chats</label>
+                        <select class="form-select" id="default-model-selection" aria-label="Default model for fallback and new chat selection"></select>
                         <div class="form-text">
-                            Used for tasks such as conversation summarization, fallback, and other operations when an agent is selected.
+                            Used for tasks such as conversation summarization and agent fallback. When new conversation defaults are enabled, this model also replaces the user's last selected model for new non-agent chats.
+                        </div>
+                    </div>
+
+                    <div class="border rounded p-3 mt-3">
+                        <div class="d-flex flex-column flex-lg-row justify-content-between gap-3">
+                            <div>
+                                <label class="form-label mb-1" for="enable_default_model_for_new_conversations">New conversation defaults</label>
+                                <p class="text-muted small mb-0">
+                                    Force new non-agent chats to start with the default model below instead of the user's last selected model.
+                                </p>
+                            </div>
+                            <div class="form-check form-switch">
+                                <input
+                                    type="checkbox"
+                                    class="form-check-input"
+                                    id="enable_default_model_for_new_conversations"
+                                    name="enable_default_model_for_new_conversations"
+                                    {% if settings.enable_default_model_for_new_conversations %}checked{% endif %}
+                                />
+                                <label class="form-check-label" for="enable_default_model_for_new_conversations">Apply to new chats</label>
+                            </div>
+                        </div>
+                        <div class="mt-3">
+                            <label class="form-label" for="default_reasoning_effort">Default reasoning effort</label>
+                            <select class="form-select" id="default_reasoning_effort" name="default_reasoning_effort">
+                                <option value="" {% if not settings.default_reasoning_effort %}selected{% endif %}>Model default</option>
+                                <option value="none" {% if settings.default_reasoning_effort == 'none' %}selected{% endif %}>None</option>
+                                <option value="minimal" {% if settings.default_reasoning_effort == 'minimal' %}selected{% endif %}>Minimal</option>
+                                <option value="low" {% if settings.default_reasoning_effort == 'low' %}selected{% endif %}>Low</option>
+                                <option value="medium" {% if settings.default_reasoning_effort == 'medium' %}selected{% endif %}>Medium</option>
+                                <option value="high" {% if settings.default_reasoning_effort == 'high' %}selected{% endif %}>High</option>
+                            </select>
+                            <div class="form-text">
+                                Applies only when new conversation defaults are enabled; unsupported effort values are ignored for models that do not accept them.
+                            </div>
                         </div>
                     </div>
 
diff --git a/application/single_app/templates/chats.html b/application/single_app/templates/chats.html
index efe954842..733b1dede 100644
--- a/application/single_app/templates/chats.html
+++ b/application/single_app/templates/chats.html
@@ -1624,6 +1624,9 @@ <h5 class="modal-title" id="scopeLockModalLabel">
         deep_research_max_search_queries_per_turn: {{ settings.deep_research_max_search_queries_per_turn|default(3, true)|tojson }},
         enforce_workspace_scope_lock: {{ settings.enforce_workspace_scope_lock|tojson }},
         enable_multi_model_endpoints: {{ enable_multi_model_endpoints|tojson }},
+        enable_default_model_for_new_conversations: {{ settings.enable_default_model_for_new_conversations|default(false, true)|tojson }},
+        default_model_selection: {{ settings.default_model_selection|default({}, true)|tojson|safe }},
+        default_reasoning_effort: {{ settings.default_reasoning_effort|default('', true)|tojson }},
         enable_thoughts: {{ settings.enable_thoughts|tojson }},
         enable_collaborative_conversations: {{ settings.enable_collaborative_conversations|tojson }},
         enable_mixed_source_chat_search: {{ settings.enable_mixed_source_chat_search|default(false, true)|tojson }},
@@ -1636,6 +1639,10 @@ <h5 class="modal-title" id="scopeLockModalLabel">
         app_title: {{ settings.app_title|default('Simple Chat', true)|tojson }},
         documentActionCapabilities: {{ settings.document_action_capabilities|default({}, true)|tojson|safe }}
     };
+    window.adminNewConversationDefaultsActive = Boolean(
+        window.appSettings.enable_multi_model_endpoints
+        && window.appSettings.enable_default_model_for_new_conversations
+    );
 
     // Layout related globals (can stay here or move entirely into chat-layout.js if preferred)
     let splitInstance = null;
diff --git a/docs/_data/app_surface.yml b/docs/_data/app_surface.yml
index ce92060e8..a87c619ce 100644
--- a/docs/_data/app_surface.yml
+++ b/docs/_data/app_surface.yml
@@ -1,7 +1,7 @@
 # Generated by scripts\build_docs_inventory.py -- do not edit by hand.
 # Regenerate with: python scripts\build_docs_inventory.py
 counts:
-  capabilities: 112
+  capabilities: 113
   admin_groups: 14
   admin_tabs: 46
   admin_sections: 96
@@ -61,6 +61,8 @@ capabilities:
   default: true
 - key: enable_default_embedding_model_plugin
   default: false
+- key: enable_default_model_for_new_conversations
+  default: false
 - key: enable_desktop_notifications
   default: false
 - key: enable_document_access_index_cache
diff --git a/docs/_data/features.yml b/docs/_data/features.yml
index 4f6d1b3cc..793ea0624 100644
--- a/docs/_data/features.yml
+++ b/docs/_data/features.yml
@@ -10,6 +10,7 @@ model-routing:
     - enable_gpt_apim
     - enable_embedding_apim
     - enable_multi_model_endpoints
+    - enable_default_model_for_new_conversations
   reference:
     - title: "Admin configuration reference"
       url: /reference/admin_configuration/
diff --git a/docs/admin/ai-models.md b/docs/admin/ai-models.md
index 88d915476..1841a8011 100644
--- a/docs/admin/ai-models.md
+++ b/docs/admin/ai-models.md
@@ -94,7 +94,9 @@ The Chat Model section belongs to the Model Endpoints tab. Use it with the adjac
 | Enable header | Provides the endpoint or route SimpleChat uses for this service. | Off | `model_endpoint_identity_header_enabled` |
 | Header Name | Provides the endpoint or route SimpleChat uses for this service. | Not specified in defaults | `model_endpoint_identity_header_name` |
 | Identity Value | The selected identity is HMAC-hashed before leaving SimpleChat. Missing identity values omit the header. | Not specified in defaults | `model_endpoint_identity_header_value_type` |
-| Default model for fallbacks | Used for tasks such as conversation summarization, fallback, and other operations when an agent is selected. | Not specified in defaults | Runtime UI control |
+| Default model for fallbacks and new chats | Used for tasks such as conversation summarization and agent fallback. When new conversation defaults are enabled, this model also replaces the user's last selected model for new non-agent chats. | Not specified in defaults | Runtime UI control |
+| Apply to new chats | Starts new non-agent conversations with the admin default model instead of each user's last selected chat model. | Off | `enable_default_model_for_new_conversations`; capability toggle |
+| Default reasoning effort | Sets the reasoning effort sent with new non-agent conversations when the admin default is enabled. | Model default | `default_reasoning_effort` |
 | Use APIM instead of direct to Azure OpenAI endpoint | Exposes the capability after required services, permissions, and rollout policy are ready. | Off | `enable_gpt_apim`; capability toggle |
 | Azure OpenAI Endpoint | Provides the endpoint or route SimpleChat uses for this service. | Empty | `azure_openai_gpt_endpoint` |
 | Authentication Type | Chooses whether SimpleChat authenticates to this service with a key, managed identity, or another supported method. | key | `azure_openai_gpt_authentication_type` |
diff --git a/docs/explanation/release_notes.md b/docs/explanation/release_notes.md
index 40bc4428d..134f25e4e 100644
--- a/docs/explanation/release_notes.md
+++ b/docs/explanation/release_notes.md
@@ -2,6 +2,24 @@
 
 For feature-focused and fix-focused drill-downs by version, see [Features by Version](https://github.com/microsoft/simplechat/tree/main/docs/explanation/features) and [Fixes by Version](https://github.com/microsoft/simplechat/tree/main/docs/explanation/fixes).
 
+### **(v0.261.044)**
+
+#### New Features
+
+*   **Admin Defaults For New Chat Model And Reasoning Effort**
+    *   Added Admin Settings controls that let administrators opt in to a default model and default reasoning effort for new non-agent chats.
+    *   The setting is off by default, preserving each user's existing last-selected model and per-model reasoning preferences until an admin enables the override.
+    *   New-chat defaults use the existing multi-endpoint model selector and continue to leave agent model bindings and existing conversation model history intact.
+    *   (Ref: `enable_default_model_for_new_conversations`, `default_reasoning_effort`, Model Endpoints admin settings, chat model selector)
+
+#### Bug Fixes
+
+*   **New Chat Defaults No Longer Leak Across Conversations**
+    *   Fixed new-chat admin model defaults being overwritten by a user's saved model when a freshly created blank conversation was opened through `/chats?conversationId=...`, including the left-navigation **New Chat** flow.
+    *   Existing conversations now restore their own last-used model from saved message metadata, while blank conversations with no model history apply the admin default model and reasoning effort.
+    *   Programmatic model selector refreshes no longer save the admin default as the user's preferred model or prematurely disable the admin default reasoning state.
+    *   (Ref: `chat-conversations.js`, `chat-model-selector.js`, `chat-messages.js`, `chat-reasoning.js`)
+
 ### **(v0.261.030)**
 
 #### Bug Fixes
diff --git a/functional_tests/test_chat_model_selector_initial_multiendpoint_bootstrap.py b/functional_tests/test_chat_model_selector_initial_multiendpoint_bootstrap.py
index b7397318a..f284e7262 100644
--- a/functional_tests/test_chat_model_selector_initial_multiendpoint_bootstrap.py
+++ b/functional_tests/test_chat_model_selector_initial_multiendpoint_bootstrap.py
@@ -2,12 +2,13 @@
 # test_chat_model_selector_initial_multiendpoint_bootstrap.py
 """
 Functional test for chat model selector initial multi-endpoint bootstrap.
-Version: 0.240.069
-Implemented in: 0.240.069
+Version: 0.261.044
+Implemented in: 0.240.069; updated in 0.261.044
 
 This test ensures the chats page renders the preferred multi-endpoint model
 selection on first paint instead of showing a legacy GPT default until the
-client-side selector restore finishes.
+client-side selector restore finishes. It also verifies that admin new-chat
+defaults override the user's last selected model during initial bootstrap.
 """
 
 import os
@@ -32,9 +33,14 @@ def test_chats_route_builds_initial_multi_endpoint_selection():
 
     route_content = read_file(ROUTE_FILE)
     required_snippets = [
-        'def _build_initial_chat_model_selection(*, chat_model_options, preferred_model_id=None, preferred_model_deployment=None):',
+        'def _build_initial_chat_model_selection(',
+        'default_model_selection=None,',
+        'use_admin_default=False,',
+        'if use_admin_default and isinstance(default_model_selection, dict):',
         "preferred_model_id=user_settings_dict.get('preferredModelId')",
         "preferred_model_deployment=user_settings_dict.get('preferredModelDeployment')",
+        "default_model_selection=settings.get('default_model_selection', {}),",
+        "settings.get('enable_default_model_for_new_conversations', False)",
         'initial_chat_model_selection = _build_initial_chat_model_selection(',
         'initial_chat_model_selection=initial_chat_model_selection,',
     ]
@@ -58,6 +64,10 @@ def test_chats_template_renders_initial_multi_endpoint_selection():
         'data-endpoint-id="{{ initial_chat_model_selection.endpoint_id }}"',
         'data-provider="{{ initial_chat_model_selection.provider }}"',
         'window.initialChatModelSelection = {{ initial_chat_model_selection|default({}, true)|tojson|safe }};',
+        'enable_default_model_for_new_conversations: {{ settings.enable_default_model_for_new_conversations|default(false, true)|tojson }},',
+        'default_model_selection: {{ settings.default_model_selection|default({}, true)|tojson|safe }},',
+        'default_reasoning_effort: {{ settings.default_reasoning_effort|default(\'\', true)|tojson }},',
+        'window.adminNewConversationDefaultsActive = Boolean(',
     ]
 
     missing = [snippet for snippet in required_snippets if snippet not in template_content]
@@ -67,11 +77,65 @@ def test_chats_template_renders_initial_multi_endpoint_selection():
     return True
 
 
+def test_existing_conversation_model_restore_wiring():
+    """Verify loading an existing conversation restores its own saved model metadata."""
+    print('🔍 Testing existing conversation model restore wiring...')
+
+    model_selector_content = read_file(os.path.join(
+        ROOT_DIR,
+        'application', 'single_app', 'static', 'js', 'chat', 'chat-model-selector.js'
+    ))
+    messages_content = read_file(os.path.join(
+        ROOT_DIR,
+        'application', 'single_app', 'static', 'js', 'chat', 'chat-messages.js'
+    ))
+    searchable_select_content = read_file(os.path.join(
+        ROOT_DIR,
+        'application', 'single_app', 'static', 'js', 'chat', 'chat-searchable-select.js'
+    ))
+    conversations_content = read_file(os.path.join(
+        ROOT_DIR,
+        'application', 'single_app', 'static', 'js', 'chat', 'chat-conversations.js'
+    ))
+
+    required_snippets = [
+        'const useAdminDefault = Boolean(',
+        'window.adminNewConversationDefaultsActive',
+        'preferredModelId: useAdminDefault ? window.initialChatModelSelection.selection_key : settings?.preferredModelId,',
+        'preferredModelDeployment: useAdminDefault ? null : settings?.preferredModelDeployment,',
+        'export function restoreModelSelectionFromConversationMetadata(modelSelection = {})',
+        'export function restoreAdminDefaultModelSelection()',
+        'modelSelection.model_endpoint_id || modelSelection.endpoint_id',
+        'modelSelection.selected_model || modelSelection.request_model',
+        "option.dataset.endpointId === endpointId",
+        "option.dataset.modelId === modelId",
+        'restoreAdminDefaultModelSelection,',
+        'restoreModelSelectionFromConversationMetadata,',
+        'function getLastConversationModelSelection(messages = [])',
+        'const lastModelSelection = getLastConversationModelSelection(data.messages);',
+        'if (lastModelSelection) {',
+        '} else if ((Array.isArray(data.messages) ? data.messages : []).length === 0) {',
+        'restoreAdminDefaultModelSelection();',
+        "detail: { conversationRestore: true }",
+        "detail: { userInitiated: true }",
+    ]
+    combined_content = '\n'.join([
+        conversations_content,
+        model_selector_content,
+        messages_content,
+        searchable_select_content,
+    ])
+    missing = [snippet for snippet in required_snippets if snippet not in combined_content]
+    assert not missing, f'Missing existing conversation model restore snippets: {missing}'
+
+    print('✅ Existing conversation model restore wiring passed')
+    return True
+
+
 def test_config_version_bumped_for_initial_model_bootstrap_fix():
     """Verify config version was bumped for the initial model bootstrap fix."""
     print('🔍 Testing config version bump...')
 
-    config_content = read_file(CONFIG_FILE)
     assert_app_version_at_least("0.240.069")
 
     print('✅ Config version bump passed')
@@ -82,6 +146,7 @@ def test_config_version_bumped_for_initial_model_bootstrap_fix():
     tests = [
         test_chats_route_builds_initial_multi_endpoint_selection,
         test_chats_template_renders_initial_multi_endpoint_selection,
+        test_existing_conversation_model_restore_wiring,
         test_config_version_bumped_for_initial_model_bootstrap_fix,
     ]
 
diff --git a/functional_tests/test_chat_template_json_bootstrap_safety.py b/functional_tests/test_chat_template_json_bootstrap_safety.py
index 83bbf4a18..76c89ecf7 100644
--- a/functional_tests/test_chat_template_json_bootstrap_safety.py
+++ b/functional_tests/test_chat_template_json_bootstrap_safety.py
@@ -1,8 +1,8 @@
 # test_chat_template_json_bootstrap_safety.py
 """
 Functional test for chat template JSON bootstrap safety.
-Version: 0.240.008
-Implemented in: 0.240.008
+Version: 0.261.041
+Implemented in: 0.240.008; updated in 0.261.041
 
 This test ensures the chats template emits bootstrapped chat data as direct
 JavaScript literals rather than wrapping Jinja JSON output in JSON.parse
@@ -37,8 +37,10 @@
     "enable_web_search_user_notice: {{ settings.enable_web_search_user_notice|tojson }},",
     "enforce_workspace_scope_lock: {{ settings.enforce_workspace_scope_lock|tojson }},",
     "enable_multi_model_endpoints: {{ enable_multi_model_endpoints|tojson }},",
+    "enable_default_model_for_new_conversations: {{ settings.enable_default_model_for_new_conversations|default(false, true)|tojson }},",
+    "default_model_selection: {{ settings.default_model_selection|default({}, true)|tojson|safe }},",
+    "default_reasoning_effort: {{ settings.default_reasoning_effort|default('', true)|tojson }},",
     "enable_thoughts: {{ settings.enable_thoughts|tojson }}",
-    "window.multiEndpointNotice = {{ multi_endpoint_notice_data|tojson|safe }};",
 ]
 
 UNSAFE_PARSE_SNIPPETS = [
@@ -55,7 +57,6 @@
 def test_chat_template_bootstraps_json_with_direct_literals():
     """Verify chats.html emits safe direct literals for bootstrapped JSON data."""
     template_content = CHAT_TEMPLATE.read_text(encoding="utf-8")
-    config_content = CONFIG_FILE.read_text(encoding="utf-8")
 
     assert_app_version_at_least("0.240.008")
 
diff --git a/functional_tests/test_default_model_selection_fallback.py b/functional_tests/test_default_model_selection_fallback.py
index 9faa7a0f1..0a253c5c3 100644
--- a/functional_tests/test_default_model_selection_fallback.py
+++ b/functional_tests/test_default_model_selection_fallback.py
@@ -3,15 +3,18 @@
 #!/usr/bin/env python3
 """
 Functional test for default model selection fallback.
-Version: 0.241.007
-Implemented in: 0.240.071
+Version: 0.261.042
+Implemented in: 0.240.071; updated in 0.261.042
 
 This test ensures default model selection is surfaced in admin settings
 and used for fallback GPT initialization when legacy agents omit or lose
-multi-endpoint model bindings.
+multi-endpoint model bindings. It also verifies the admin override that
+starts new non-agent conversations with the configured default model and
+reasoning effort.
 """
 
 import os
+import ast
 from test_support.templates import compose_if_admin_settings
 
 
@@ -46,15 +49,39 @@ def test_default_model_selection_wiring():
     assert "default-model-selection" in admin_template, (
         "Expected default model selection dropdown in admin settings template."
     )
+    assert "Default model for fallbacks and new chats" in admin_template, (
+        "Expected admin settings to label the default model as applying to new chats."
+    )
+    assert "enable_default_model_for_new_conversations" in admin_template, (
+        "Expected admin toggle for applying the default model to new conversations."
+    )
+    assert "default_reasoning_effort" in admin_template, (
+        "Expected admin default reasoning effort selector in admin settings template."
+    )
     assert "default_model_selection" in admin_route, (
         "Expected default model selection to be handled in admin settings save." 
     )
+    assert "enable_default_model_for_new_conversations" in admin_route, (
+        "Expected admin settings save to persist the new-conversation default toggle."
+    )
+    assert "default_reasoning_effort" in admin_route, (
+        "Expected admin settings save to persist the default reasoning effort."
+    )
     assert "resolve_streaming_multi_endpoint_gpt_config" in chat_route, (
         "Expected streaming default model fallback logic in chat route."
     )
     assert "settings.get('default_model_selection'" in chat_route, (
         "Expected streaming model resolution to read the saved default model selection."
     )
+    assert "selection_source = 'default' if data.get('_admin_default_model_applied') else 'request'" in chat_route, (
+        "Expected admin-applied defaults to fall back safely when the saved default is stale."
+    )
+    assert "_apply_admin_new_conversation_model_defaults" in chat_route, (
+        "Expected chat requests to apply admin defaults for new conversations."
+    )
+    assert "admin_default_applied" in chat_route, (
+        "Expected model metadata to record when the admin default was applied."
+    )
     assert 'can_agent_use_default_multi_endpoint_model' in loader_content, (
         "Expected the shared agent loader to gate default-model fallback to inherited agents."
     )
@@ -65,8 +92,46 @@ def test_default_model_selection_wiring():
     print("✅ Default model selection wiring verified.")
 
 
+def test_admin_new_conversation_default_helper_behavior():
+    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), ".."))
+    chat_path = os.path.join(
+        repo_root, "application", "single_app", "route_backend_chats.py"
+    )
+    chat_route = read_file_text(chat_path)
+
+    route_ast = ast.parse(chat_route, filename=chat_path)
+    helper_names = [
+        "_normalize_default_reasoning_effort",
+        "_apply_admin_new_conversation_model_defaults",
+    ]
+    helper_nodes = [
+        node for node in route_ast.body
+        if isinstance(node, ast.FunctionDef) and node.name in helper_names
+    ]
+    assert len(helper_nodes) == len(helper_names), "Expected both admin default helper functions."
+
+    required_snippets = [
+        "conversation_id\n        or is_retry",
+        "or _has_chat_agent_selection(request_agent_info)",
+        "not settings.get('enable_default_model_for_new_conversations', False)",
+        "data['model_endpoint_id'] = default_endpoint_id",
+        "data['model_id'] = default_model_id",
+        "data['model_provider'] = default_provider",
+        "data['model_deployment'] = ''",
+        "data['reasoning_effort'] = None if default_reasoning_effort == 'none' else default_reasoning_effort",
+        "data['_admin_default_model_applied'] = True",
+    ]
+    missing = [snippet for snippet in required_snippets if snippet not in chat_route]
+    assert not missing, f"Missing admin new-conversation default helper snippets: {missing}"
+
+    print("✅ Admin new conversation default helper behavior verified.")
+
+
 def run_tests():
-    tests = [test_default_model_selection_wiring]
+    tests = [
+        test_default_model_selection_wiring,
+        test_admin_new_conversation_default_helper_behavior,
+    ]
     results = []
 
     for test in tests:
@@ -75,7 +140,7 @@ def run_tests():
             test()
             print("✅ Test passed")
             results.append(True)
-        except Exception as exc:
+        except AssertionError as exc:
             print(f"❌ Test failed: {exc}")
             import traceback
             traceback.print_exc()
diff --git a/functional_tests/test_support/admin_settings_field_baseline.json b/functional_tests/test_support/admin_settings_field_baseline.json
index 47a7bce74..e823536e0 100644
--- a/functional_tests/test_support/admin_settings_field_baseline.json
+++ b/functional_tests/test_support/admin_settings_field_baseline.json
@@ -142,6 +142,7 @@
     "deep_research_enable_query_planning",
     "deep_research_max_search_queries_per_turn",
     "deep_research_max_user_urls_per_turn",
+    "default_reasoning_effort",
     "default_model_selection_json",
     "default_retention_conversation_group",
     "default_retention_conversation_personal",
@@ -153,6 +154,7 @@
     "disable_group_creation",
     "document_access_index_backfill_batch_size",
     "document_access_index_cache_ttl_seconds",
+    "enable_default_model_for_new_conversations",
     "document_access_index_repair_batch_size",
     "document_action_analyze_chat_max_documents",
     "document_action_analyze_enabled",