For comparison sake, realize that American Jenny Simpson has only run 3:58 or faster in her life 5 times, the most recent coming in the DL finale in Zurich in September of 2016 when she ran 3:58.54. In that race, Simpson ran 3:58 off of a 2:09 opening 800 and her last lap was just 62.2. Muir just ran 3:58 off of a 2:11 opening 800 with her last lap in London being a sensational 57.54. Remember, last year, we raved about Shelby Houlihan closing USAs in 57.67 but that was a 4:05 race.
Muir's 57 certainly wasn't the the only time that someone has closed a 1500 in London in 57. At the London Worlds in 2017, Faith Kipyegon won the world title with a 57.9 last lap but that was a 4:02 race. In the 2012 Olympic final in London, one of the most drug upped races in women's track and field history, Turkey's Asli Cakir Alptekin crossed the finish line first after a 57.9-58.0 last lap but that was a 4:10 race.
A 57 in a 3:58? That may be unprecedented. Does anyone remember a similar close?