Adobe transitioned Speech to Text from a paid add-on (it used to cost extra!) to a standard feature included in your Premiere Pro subscription. Here is the breakdown of how the "free" aspect works:

You might be thinking, "Can’t I just use a free website to generate subtitles?" You could, but the workflow is clunky. You have to export your video, upload it to a site, download an SRT file, and import it back into Premiere.