Are Slack messages deleted after a year on the free plan?

Yes. Slack states that messages and files more than one year old will be permanently deleted, and that since 26 August 2024 data older than one year may be deleted on a rolling basis from free workspaces.

Does upgrading Slack restore old messages?

It restores the band between 90 days and one year, which was hidden rather than deleted. It cannot restore anything older than a year, because that content has already been deleted.

Can you still read Slack messages older than 90 days?

Q: Can you still read Slack messages older than 90 days?

On the free plan, messages older than 90 days are hidden rather than deleted for the first year, and upgrading makes them visible again. Slack permanently deletes messages and files more than one year old from free workspaces, on a rolling basis, and that cannot be recovered by upgrading.

Hidden, not deleted — for the first year. On the free plan you can view and search the last 90 days; Slack hides what is older "to make room for new ones", and upgrading brings it back. After that it is gone: "messages and files more than one year old will be permanently deleted."

The timeline, in Slack's own words

Age of the message	Free plan	Recoverable by upgrading
0 to 90 days	"You can view and search messages and files from the last 90 days."	Not needed
90 days to 1 year	Hidden from view and search	Yes
Over 1 year	"Permanently deleted"	No

The one-year deletion is not a theoretical policy. Slack's own note is that from 26 August 2024, "Customer Data — such as messages and file history — older than one year may be deleted on a rolling basis from workspaces on the free plan." Rolling is the word that matters: there is no deadline to prepare for, because every day another day falls off the end.

So the answer depends on which question you are asking

"Can I see last spring's thread?" If the workspace is under a year old at that point, yes, by upgrading. The messages are still there.
"Will upgrading in month fourteen get month one back?" No. That content is deleted, and the upgrade has nothing to restore.
"Is there a trick?" No. Search, integrations and third-party viewers all read the same workspace through the same API, and none of them can return data Slack has deleted.

What to do today, in order

Export now, before you decide anything else. An export is reversible; deletion is not. A workspace owner can request one from the workspace settings, and what arrives is a zip.
Check what the export actually contains. Slack is explicit that a JSON export "does not contain any files from the workspace" — you get URLs pointing back at Slack instead. If attachments matter, they need collecting separately, and they are subject to the same one-year rule.
Make the archive searchable where it sits. A zip nobody can query is a backup, not an archive. The structure is simple once you have seen it: we wrote up how to search a Slack JSON export.
Decide about upgrading separately. Paying restores visibility for the 90-day-to-one-year band. It does not change what has already been deleted, and it is a subscription against a problem the export solves once.

The part that is worth building once

The reason people care about year-old Slack is almost never the messages. It is one decision — when did we drop the mobile build, who agreed the price, what did we promise that customer — and the answer is spread across three threads nobody can name.

That is the job Nico's Slack app does: four years of history, answerable, on your own Mac, without granting anyone a workspace token and without the export leaving the machine.

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