I think it's been noticeable since the start of the year. Especially noticeable during the first round of Davis Cup (maybe because of wardrobe + haricut at the time). Though many don't really like the outfit he wore today, I think it helped emphasize that he's bulked up.
For sure, his calves, neck, and arms seem to have bulked up earlier this year imo.
Some have commented on it as well.
I also think Hewitt has bulked up too. He wears such loose/baggy clothes it's hard to tell though.