This is recent:
"Anticipated for 2021, the safety barrier will now be completed in 2023, officials with the Golden Gate Bridge, Highway and Transportation District said Wednesday."
Dec 12, 2019
Note: "completed"
I'd imagine that doesn't mean (large?) portions couldn't be installed before it's fully completed.
The pix make it appear that some has been done, but those are probably artist renditions. We need someone bay side to report directly.
Seems the entire net may be being constructed off-site in Richmond.
May 17, 2019
........................
"Now the contractor is pulling double shifts, closing three lanes of traffic five nights a week, while 50 workers lift steel and other equipment over the side of the bridge. During the day, another 50 workers toil on the platforms. Five of them jut out from beneath the bridge deck, and AECOM is building a sixth, Mulligan said."
Sure sounds ongoing....