diff --git a/docs/api/rest.md b/docs/api/rest.md
index 09c9c44..d225143 100644
--- a/docs/api/rest.md
+++ b/docs/api/rest.md
@@ -40,6 +40,7 @@ Chat upload limits:
 ```
 - OpenAI model lists are filtered to models that are expected to work with the backend's Responses API implementation.
 - `hermes-agent` is included only when `HERMES_AGENT_API_KEY` is configured. Set it to Hermes `API_SERVER_KEY`, or any non-empty value if that local server does not require auth. `HERMES_AGENT_API_BASE_URL` defaults to `http://127.0.0.1:8642/v1`; set `HERMES_AGENT_MODEL` only when you need an additional fallback/override model id.
+- The backend loads provider model lists at startup and refreshes them about once every 24 hours. If a later provider refresh fails, the response keeps the last loaded model list for that provider and sets `error` to the latest failure message.
 
 ## Active Runs
 
diff --git a/server/src/index.ts b/server/src/index.ts
index e7c52bc..e79e9d1 100644
--- a/server/src/index.ts
+++ b/server/src/index.ts
@@ -5,7 +5,7 @@ import swaggerUI from "@fastify/swagger-ui";
 import sensible from "@fastify/sensible";
 import { env } from "./env.js";
 import { ensureDatabaseReady } from "./db-init.js";
-import { warmModelCatalog } from "./llm/model-catalog.js";
+import { startModelCatalogRefreshLoop, warmModelCatalog } from "./llm/model-catalog.js";
 import { registerRoutes } from "./routes.js";
 
 const app = Fastify({
@@ -21,6 +21,7 @@ const app = Fastify({
 
 await ensureDatabaseReady(app.log);
 await warmModelCatalog(app.log);
+const stopModelCatalogRefreshLoop = startModelCatalogRefreshLoop(app.log);
 
 await app.register(cors, {
   origin: true,
@@ -80,6 +81,10 @@ app.setErrorHandler((err, req, reply) => {
   });
 });
 
+app.addHook("onClose", async () => {
+  stopModelCatalogRefreshLoop();
+});
+
 await registerRoutes(app);
 
 await app.listen({ port: env.PORT, host: env.HOST });
diff --git a/server/src/llm/model-catalog.ts b/server/src/llm/model-catalog.ts
index 411eee2..5e18dc7 100644
--- a/server/src/llm/model-catalog.ts
+++ b/server/src/llm/model-catalog.ts
@@ -13,6 +13,7 @@ export type ModelCatalogSnapshot = Partial<Record<Provider, ProviderModelSnapsho
 
 const baseProviders: Provider[] = ["openai", "anthropic", "xai"];
 const MODEL_FETCH_TIMEOUT_MS = 15000;
+const MODEL_CATALOG_REFRESH_INTERVAL_MS = 24 * 60 * 60 * 1000;
 
 const modelCatalog: ModelCatalogSnapshot = {
   openai: { models: [], loadedAt: null, error: null },
@@ -20,6 +21,8 @@ const modelCatalog: ModelCatalogSnapshot = {
   xai: { models: [], loadedAt: null, error: null },
 };
 
+let catalogRefreshPromise: Promise<void> | null = null;
+
 function getCatalogProviders(): Provider[] {
   return isHermesAgentConfigured() ? [...baseProviders, "hermes-agent"] : baseProviders;
 }
@@ -86,17 +89,42 @@ async function refreshProviderModels(provider: Provider, logger?: FastifyBaseLog
     logger?.info({ provider, modelCount: models.length }, "model catalog loaded");
   } catch (err: any) {
     const message = err?.message ?? String(err);
+    const previous = modelCatalog[provider];
+    const fallbackModels = provider === "hermes-agent" && env.HERMES_AGENT_MODEL ? [env.HERMES_AGENT_MODEL] : [];
     modelCatalog[provider] = {
-      models: provider === "hermes-agent" && env.HERMES_AGENT_MODEL ? [env.HERMES_AGENT_MODEL] : [],
-      loadedAt: new Date().toISOString(),
+      models: previous?.models.length ? previous.models : fallbackModels,
+      loadedAt: previous?.loadedAt ?? null,
       error: message,
     };
     logger?.warn({ provider, err: message }, "failed to load provider model catalog");
   }
 }
 
+export async function refreshModelCatalog(logger?: FastifyBaseLogger) {
+  if (catalogRefreshPromise) return catalogRefreshPromise;
+
+  catalogRefreshPromise = Promise.all(getCatalogProviders().map((provider) => refreshProviderModels(provider, logger)))
+    .then(() => undefined)
+    .finally(() => {
+      catalogRefreshPromise = null;
+    });
+
+  return catalogRefreshPromise;
+}
+
 export async function warmModelCatalog(logger?: FastifyBaseLogger) {
-  await Promise.all(getCatalogProviders().map((provider) => refreshProviderModels(provider, logger)));
+  await refreshModelCatalog(logger);
+}
+
+export function startModelCatalogRefreshLoop(logger?: FastifyBaseLogger) {
+  const timer = setInterval(() => {
+    void refreshModelCatalog(logger);
+  }, MODEL_CATALOG_REFRESH_INTERVAL_MS);
+  timer.unref?.();
+
+  return () => {
+    clearInterval(timer);
+  };
 }
 
 export function getModelCatalogSnapshot(): ModelCatalogSnapshot {