The 49ers announced the change on Twitter:
Beathard went on to complete 19 of 36 passes for 245 yards, a touchdown and an interception as the 49ers lost 26-24. After the game, head coach Kyle Shanahan announced Beathard would be the team's starting quarterback going forward.
Hoyer signed a two-year, $12 million contract with the 49ers in March. The journeyman was only a stopgap option as the organization continues to look for its quarterback of the future.
The 32-year-old Michigan State product had completed 59.3 percent of his throws for 1,211 yards with four touchdowns and four interceptions across his five starts this season. He was 4-of-11 for 34 yards before getting taken out against Washington.
Shanahan previously said they needed more production from the position following the team's Week 4 overtime loss to the Arizona Cardinals.
"I think he needs to play better, and I think we need to play better around him," he told reporters. "It's similar to what I said last night, when you have the time and you've got guys open, you need to hit them. And I thought he struggled with that at times last night, which I know he can do better, and he does also, but I also know when he did make some key throws, guys weren't great at catching them for him either."
Beathard, 23, was the team's third-round selection in the 2017 NFL draft out of Iowa. He connected on 58.1 percent of his throws for 5,562 yards with 40 touchdowns and 19 interceptions in 40 appearances for the Hawkeyes, including two seasons as the full-time starter.
The Tennessee native put together a solid preseason for the Niners. He went 26-of-45 for 401 yards with four TDs and one pick to post a 107.7 passer rating. He also ran for 85 yards and a score on six rushing attempts.
After beating out Matt Barkley for the backup job, Beathard said the biggest key to success would be getting on the same wavelength as Shanahan, per Cam Inman of the Bay Area News Group.
"First off, I had to learn the offense and think how he thinks as much as possible, because it's his offense," he said. "He goes through every play in his head just as a quarterback would. You want to try and be on the same page as he is and think like him, so we're on the same page as much as possible."
Ultimately, expectations should be kept within reason given the fact Beathard is taking the reins of an aerial attack that lacks weapons outside of Pierre Garcon. There will be growing pains along the way, especially against the league's better secondaries.
It's still a switch worth making for the Niners, though. They need to get a chance to see what type of potential the rookie has before heading into the offseason, when the quarterback position could once again be atop the front office's to-do list.