Yep, transcoding (quality options) are only available to Twitch Partners, and non-partners who surpass a certain (undefined and changing) viewer level (who then keep them until the end of their stream).
This is a Twitch-side thing, not something you can turn on and off in OBS. Though Twitch *has* mentioned considering allowing streamers to send multiple quality levels of stream. But that'll eat more CPU and bandwidth, if they ever DO implement it.