This question already has an answer here:
Standard currently consists of the following sets
- Aether Revolt
- Hour of Devastation
- Rivals of Ixalan
The next rotation will occur when the set after Core 2019 releases. At that time Kaladesh, Aether Revolt, Amonkhet and Hour of Devastation will rotate.
We are still in the Ixalan block with the most current release of Rivals of Ixalan, and it is in the current system the most recent three blocks that are standard legal. That would mean Kaladesh, Amonkhet and Ixalan.
Also, according to Gatherer, both the Sanctum and the Mimic are legal in standard. So even if the Kaladesh block had rotated out, if Gatherer isn't up to date, how could you expect that every single contributor to deck sites is?
Also note that Rivals of Ixalan is the last release of the two-set block paradigm that has been the release model of MtG since Battle for Zendikar in October 2015. From now on, beginning with the release of Dominaria in April, they will release three expansions and a core set each year, going back to something similar to what was before Battle for Zendikar, only not separated in blocks. You can read what Mark Rosewater has to say about the change here.
The Kaladesh block will be standard legal until the release of the set codenamed "Spaghetti" is released in the fall of this year, and the Amonkhet block will also rotate out simultaneously.