When Nintendo usually releases a Nintendo Switch firmware update, it results in a change in the version number and, at the very least, a few changes that have been made confirmed via patch notes. For these updates to complete, the console must restart itself.
But every now and then, the company will release a firmware update that doesn’t require a reboot. These non-reboot updates are usually very minor and usually don’t have patch notes published for them. In fact, the version number isn’t even changed when Nintendo releases them. Nevertheless, they are a very important thing. For example, Nintendo released one tonight. You can see the tweet breaking the news below, along with what the update changed.