Why Upgrading to Laravel 13 Might Silently Log Out All Your Users

A friend of mine upgraded a Laravel app to version 13 last month. The deploy looked clean. No errors, no failed migrations. Then the support tickets started. Users kept saying they'd been logged out, over and over, for no reason. Nothing in the code had changed around authentication. The cause turned out to be something most upgrade checklists mention only in passing, if at all. If you're planning a Laravel 13 upgrade, or you've already done one and something feels slightly off, this is worth five minutes of your time.

Two small changes that add up to one big problem

Laravel's own official upgrade guide lists these as low and medium impact. Individually, that's fair. Together, on a production app, they can quietly log out every single user at once. Here's what's actually happening.

Change one: cache and session key formats changed

If your app never explicitly set CACHE_PREFIX, REDIS_PREFIX, or SESSION_COOKIE in its environment file, Laravel was generating those values for you automatically, based on your app name. In Laravel 13, the format of that automatic generation changed. Underscores became hyphens. So a cache prefix that used to look like myapp_cache_ now looks like myapp-cache-, and a session cookie named myapp_session becomes myapp-session. That sounds harmless until you think about what a session cookie actually is. It's a small piece of data, explained well on Wikipedia's HTTP cookie page if you want the full background, that the browser holds onto and sends back on every request so the server knows who you are. After the upgrade, the browser is still holding a cookie with the old name. The server is only looking for the new one. As far as Laravel is concerned, that visitor was never logged in. Every active session breaks at once, the moment the new code goes live.

Change two: session serialization format changed too

Separately, Laravel's default application skeleton now stores session data as JSON instead of PHP's native serialization format. This is a real security improvement, since it closes off a class of deserialization attacks. But if you're upgrading an existing app and you sync your config files to match the new Laravel 13 skeleton, this setting can flip along with everything else. Every session stored under the old format becomes unreadable, and again, everyone gets logged out. Neither change breaks your code. Neither one throws an error. That's exactly why it's easy to miss during testing and only shows up once real users hit it in production.

Why this also affects your Redis memory budget

If you're running Redis for object caching, and you followed the sizing approach from our Redis memory budgeting guide, this matters even more. When the cache prefix changes, Laravel doesn't clean up the old keys. It just starts writing new ones under the new prefix. The old keys sit there, still consuming whatever slice of RAM you carefully budgeted, until Redis eventually evicts them under memory pressure. On a small VPS where you sized Redis down to something like 128 MB on purpose, that's not nothing. You end up with two generations of cache keys competing for the same tight ceiling, right after an upgrade, which is exactly the wrong time to have your cache working less efficiently than usual. The same goes if you're running a Supervisor-managed queue worker alongside your app. A queue worker process holds its own database and cache connections open for a long time, so it's worth restarting it right after this kind of upgrade rather than assuming it'll pick up new config on its own.

The fix, before you upgrade

Check your current .env file first:

grep -E "CACHE_PREFIX|REDIS_PREFIX|SESSION_COOKIE" .env

If nothing comes back, your app has been relying on the automatic fallback this whole time, and you're exposed to this issue. Set all three explicitly, using your current values so nothing changes when you upgrade:

CACHE_PREFIX=myapp_cache_
REDIS_PREFIX=myapp_database_
SESSION_COOKIE=myapp_session

You can pull your current values straight from a running Redis instance if you're not sure what they are:

redis-cli --scan --pattern "*cache*" | head -5

Look at the prefix on those existing keys and match it exactly. For the session serialization setting, decide on purpose rather than by accident. If you don't store PHP objects in the session and you're fine asking users to log in again once, switching to json is the more secure choice going forward. If you'd rather avoid a mass logout entirely, keep session.serialization set to php in config/session.php during the upgrade, and revisit the switch later on your own schedule.

Test it properly before it reaches production

Log into a staging copy of your app before the upgrade. Upgrade it. Then check, without logging in again, whether you're still authenticated. If you are, the fix worked. If you're not, one of these two settings still isn't pinned down. This is worth doing on a real staging environment, not just locally, since the whole failure mode depends on real cookies and real cache data that a fresh local install won't have.

Where to keep up with changes like this

Laravel 13 shipped on March 17, 2026, announced by Taylor Otwell at Laracon EU. The official Laravel account on X and the official Laravel YouTube channel are both worth following directly. Laracon talks and release walkthroughs go up there first, usually before the smaller changes like this one get written up anywhere else. Reading the official release notes alongside the upgrade guide is still the most reliable way to catch something like this before it reaches your users instead of after.

I verified these Laravel 13 changes directly against Laravel's official upgrade guide as of August 2026.