When you live in Alaska, and use AS miles to book space on one of their partners like CX out of SFO to HKG, or KLM out of LAX to AMS, AS includes as part of the award the connecting space in F from ANC through Seattle to SFO or LAX. If F saver space is not available, one must accept Y saver.
When you plan ahead, it is easy to get J or F space on these numerous partners
but virtually impossible to find F saver space between ANC and SEA to connect to and from the international gateway on or near the same day.