Previewed at WWDC, launching in the fall.
Some OS X Yosemite Users Plagued With Wi-Fi Connection Issues
According to the complaints, Wi-Fi connections are sometimes extremely slow, resulting in long loading times, and in some cases, users are seeing their Wi-Fi connections disconnect continually after just a few minutes of being connected.
Since upgrading to Yosemite, my previously-stable (with Mavericks) wifi connection keeps dropping. I have to click the wifi icon and re-select my network every minute or two. I have turned off bluetooth and uninstalled/reinstalled wifi and my networks. I have rebooted multiple times. No luck so far. It appears that others are having similar problems.The problems appear to be affecting a wide range of different MacBooks, different routers, and users in different locations. A number of different fixes have been suggested on various forums, but it does not appear that any one solution works for everyone, suggesting there may be an issue with Yosemite that needs to be addressed in a future update.
Some users have had luck disabling Bluetooth, turning off Handoff, creating new Network Locations, doing a clean Yosemite install, setting a router to "G-mode only," turning off Dropbox syncing, disabling WPA router encryption, or turning off all proxies in Network preferences, but other users have not been able to solve their Wi-Fi problems at all even attempting all of the above listed solutions. Swapping to a 2.4GHz band has, however, worked for a large number of users.
Apple support representatives have supplied users with different solutions that have included removing excess preferred networks in the Network section of System Preferences and resetting the System Management Controller.
OS X Daily has written an in-depth tutorial on how to fix the Wi-Fi problems in OS X Yosemite, which involves several steps like deleting preference files, creating custom DNS settings, and refreshing the discoveryd service, but for users who can't find a fix, the site recommends downgrading to OS X Mavericks until Yosemite is updated.
Users attempting any of the highly technical fixes above should make a Time Machine backup ahead of time and use caution when deleting any system files. Thus far, there is no word on when a Yosemite update might come as Apple has not yet released any betas to developers.