AMC announced last week that the midseason premiere of The Walking Dead was free to watch online at AMC's website for a limited time. Then, the network announced the availability of the episode on Android, iPhone, iPad and Kindle Fire.
Today, AMC uploaded the entire episode to YouTube, which you are now free to watch. Presumably, the video will remain watchable for the same duration as AMC's own video (which is until March 10th).
The episode set a series record for viewers the night it originally aired.
AMC is only offering this particular episode for free, but the one that follows this one is now available to stream online elsewhere for a price.