And this year, you will see some security changes. Some will be visible, like surveillance, but other parts will be under the radar.
"We really tell our runners and we tell everybody out there in the community: if you see something, say something, and we all take responsibility for everybody's safety out there," said Alex Bennett, the race's director of events.
Organizers say you will see added security out there: Police will be checking the course overnight Friday into Saturday morning. Police dogs will do bomb sweeps of local streets before the runners take off.
It's all in the wake of the Boston Marathon bombings.
"I've run several races since then and there's been heightened security and heightened awareness in all the races I've run," said 54-year-old Kate Gates, a 45-time marathoner who wasn't able to complete the Boston race after the bombs went off. "When you pick up your number, when you come into the start line, when you're running the race, procedures have changed dramatically."
First time half-marathoner Chelsea Halliday noticed the extra security too.
"It makes me safer, actually," she said. "I actually saw a policeman carrying out a bag, so don't know if there might've been something."
If anything, the terror attack has made some runners more determined.
"For the people who lost their lives in Boston, of course, it makes you want to run for them," said Arnold Mangila of West Seattle.
And organizers, more than ever, are sending a message: They are all Boston strong.
"You don't let the fear of what might happen control you," said Frank Shorter, a gold medal marathoner, who was in Munich during the 1972 Olympic attacks as well as at the 2013 Boston Marathon. "And I think that's what we've been seeing."
There are other Boston remembrances planned for this weekend as well. There will be a moment of silence at the start line to pay tribute, and all runners will be given this wristband with Boston's date and the message "run now."