Do high speed trains sell out from Naples to Florence?

I think what you are running into is a major rail construction project in Florence, a bridge replacement. Trenitalia is unsure of the project schedule requirements so is holding off on releasing these trains for sale at this time. No high speed trains for sale on this route July 6 to July 9.
They may show up a later date with replacement buses around the construction and into Florence SMN.

They never run out. There are several trains every hour, so at most, they run out of tickets in the standard class, so you have to buy a ticket in a more expensive class, or take the next train.

Regarding July there are several major work projects on the line. besides the replacement of an overpass in Florence, they are upgrading the rail traffic signaling system by installing the ERTMS (European Rail Traffic Management System) a standardized system intended to replace the various national system. That work is scheduled in June and July, so you might have run into that issue.

It's the bridge, RFI has recently updated the timetable of the planned works: https://i.postimg.cc/wjWtMtYd/Immagine-2026-04-14-205937.jpg Based on what happened in the past they'll open the bookings around June 14.

The ERMTS works were completed last Sunday: https://i.postimg.cc/4xGMydbt/Immagine-2026-04-14-210017bis.jpg All sections have been upgraded.

Any updates on high speed train release dates for July 6-9 (specifically July 7) for travel from Florence to Naples?

See above post by marco

I boarded this train yesterday for the Naples to Rome segment. Our train car was about 50% full.

...and Yesterday was May 3, the last day of the longest week-end in 2026. So now you all know for sure that trains do not sell out.

Thank you, I was just wondering if there were updates regarding bridge construction which is currently affecting high speed train bookings specifically on July 7. If the high speed trains for this date are likely to be available again for booking in mid-June, like Marco predicted in his post in April, then we can wait to book. However, if the construction is expected to continue to significantly restrict travel between Florence to Naples, we may need to change our reservation dates soon (but would prefer to avoid this if possible). Currently the only available options on Trenitalia are 8+ hours. Nothing is available from Italo for that date. Any updates are appreciated!!

The bridge construction is set. July 6 to July 9. The issue is for Trenitalia and Italotreno to get the substitute bus arrangements figured out. They may reduce the train schedule to keep things organized. If you are in Florence, I suspect you can board a train at Florence Campo di Marte station, as that is before the bridge construction.

June 14 is the date of European-wide train schedule adjustment. Most of the schedules are already set, but a few things are still up in the air, like some regional trains and this project. I would suggest keep checking the schedule every week to see what unfolds.

The buses were "booked" in 2025, they needed them first in January 2026. The issue is that the crane that can lift the new iron bridge must arrive by ship from he US. Then they must unload it in Livorno, take it to Florence by road and reaseemble it in central Florence.

Merchant ships can be late, Trenitalia will never update the schedules and start selling tickets from the 5th t.o 9th of July before they are 100% sure the ship is on time and the works will be carried out as planned. Just be gratefull it's crossing the atlantic ocean, far from Hormuz.