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The Boston Red Sox have reportedly agreed to terms with California prep shortstop Marcelo Mayer, the No. 4 pick in last week's amateur draft, on a contract that includes a signing bonus of $6.664 million, or full slot value, according to's Jim Callis. The Athletic's Chad Jennings had tweeted earlier in the day that Mayer appeared to be at Fenway Park based on a scoreboard message.

Mayer, whose signing bonus will top the one received by No. 1 pick Henry Davis and will likely remain the highest in the class until Jack Leiter signs with the Texas Rangers, entered the draft ranked by CBS Sports as this summer's best prospect. Here's what we wrote about him at the time:

Mayer makes the leap from No. 5 in the preseason to No. 1 now, but this spot could have gone to a couple other players without fuss. His boosters within the industry believe that he's the best player in the class: a potential 15-to-20-home-run-hitting shortstop who can deliver a good average and professional at-bats all the while. He isn't a fast runner, yet the smoothness of his defensive actions enable him to appear as though he's moving at a higher frames per second than the average prep shortstop. Depending on the extent of his projected power gains, he could finish his development with four plus tools (everything but the run), giving him a lofty ceiling that merits the top selection. Mayer is far more likely to become the first prep shortstop to go No. 1 since Royce Lewis in 2017 than he is to attend class in-person at USC this fall.

Presuming Mayer does officially sign with the Red Sox, he'd become the best prospect in a farm system that includes notable youngsters like infielder Jeter Downs (acquired as part of the Mookie Betts trade) and first baseman Triston Casas.