Mintplex-Labs/anything-llm · error

Fallback model is required.

Error message

Fallback model is required.

What it means

Validation error from ModelRouter.update relayed by PUT /model-routers/:id: the payload omitted or blanked the fallback model field, which is required so the router always has a model to fall back to.

Source

Thrown at server/endpoints/modelRouter.js:82

        if (error) return response.status(400).json({ router, error });
        await Telemetry.sendTelemetry("model_router_created");
        return response.status(200).json({ router });
      } catch (e) {
        console.error(e);
        response.sendStatus(500);
      }
    }
  );

  app.put(
    "/model-routers/:id",
    [validatedRequest, flexUserRoleValid([ROLES.admin])],
    async (request, response) => {
      try {
        const { id } = request.params;
        const data = reqBody(request);
        const { router, error } = await ModelRouter.update(Number(id), data);
        if (error) return response.status(400).json({ router, error });
        ModelRouterService.invalidateRouter(Number(id));
        return response.status(200).json({ router });
      } catch (e) {
        console.error(e);
        response.sendStatus(500);
      }
    }
  );

  app.delete(
    "/model-routers/:id",
    [validatedRequest, flexUserRoleValid([ROLES.admin])],
    async (request, response) => {
      try {
        const { id } = request.params;
        const success = await ModelRouter.delete(Number(id));
        if (!success)
          return response

View on GitHub (pinned to 3aec848f28)

Solutions

1. Include the fallback model field in the update.
2. Verify the model name is valid for the chosen provider.

When it happens

Trigger: Thrown at server/endpoints/modelRouter.js:82 when the library encounters an invalid state.

Common situations: Router update missing the fallback model.

AI-assisted analysis of Mintplex-Labs/anything-llm@3aec848f28 (2026-08-18). Data as JSON: /api/errors/baa7911a83475bd6. Report an issue: GitHub.