Preview deploys are unusably slow

[hey-august]

Component

Docs

Priority

P2 - Medium (Would be helpful)

SDK Language(s)

No response

Bug Description

Steps to reproduce:

• Generate a deploy preview with fern generate --docs --preview

Expected behavior

• Site load and navigation should take a reasonable amount of time once the preview builds.

Actual behavior
Please see attached screen recording. The below times are approximate, and taken from the screen recording, but representative of our team's recent experience with deploy previews.

Event	Recorded load time
Initial load	~14s
Navigate from homepage to Platform product	~58s
Navigate between products	~20s

Environment details

• macOS 15.7.3
• Tested in Safari, Firefox, and Chrome

Versions

Fern CLI version: 5.44.4

Workaround

I am not aware of a real workaround to the issue. "Local" builds are affected the exact same way, since they also run on Fern's preview servers.

After enough clicking around, load times sometimes start to improve for some navigation actions. But some pages continue to load very slowly. I can't identify a pattern to which pages will load slowly or not - it seems random.

Are you interested in contributing a fix?

No

[Devon-White]

Can confirm this is a very frequent experience when using a deploy preview or a dev build locally. Sometimes if you open the same link in a new tab it will load before the tab you clicked the link on.

[broady]

Hi all,

I'm working on getting these faster. We are introducing incremental, content-addressed publishing, which will speed up previews a lot.

The CLI will only upload content that's changed, negotiating any missing or changed content when a publish is started.

The PR tracking this on the CLI side is #16097

This will be opt-in/experimental while we validate and verify, then turned on a future CLI version as the new default.

[hey-august]

Thanks for the update!

This sounds like it would speed up uploads - but in skimming the thread, I don't see that it would help navigation speeds?

Upload times have not been a problem for us. Our issue is super slow navigation between pages in the built preview.