The developer-only beta of iOS 17 is available to all users, seemingly by mistake.
As first spotted by Twitter user Connor Jewiss, iOS 17 is listed as available for download in the beta section of Settings. This is the same release that has been, correctly, released for developers.
Doubtlessly, Apple will pull the release shortly, but in the meantime, AppleInsider recommends — urges — that no one download it. Beta test versions are, by definition, far from ready for general use and it is possible to permanently lock up an iPhone if there is a problem.
Apple's iOS 17 will enter public beta in July and then iterate through many versions until the final release, which is expected around September or October 2023.
Update: Apple has introduced a free tier for the developer program that includes beta access, so this wasn't a mistake. All users need is a free Apple ID to enroll in the free tier of the developer program.