This document outlines the process by which flags in chromium expire and are removed from the codebase, and describes which flags are about to expire. This is the authoritative list of flags that are expiring and being removed. This document only describes entries in chrome://flags, not command-line switches (commonly also called command-line flags). This process does not cover command-line switches and there continue to be no guarantees about those.
If you are a user or administrator of Chrome and are using (or think you need to use) a flag to configure Chromium for your use case, please file a bug or email flags-dev@, because that flag will likely be removed at some point. If you are a chromium developer, please carry on using flags as normal :)
Flags have never been a supported configuration surface in Chromium, and we have never guaranteed that any specific flag will behave consistently or even continue to exist. This document describes a process for removing flags that have been around for long enough that users might have come to rely on their ongoing existence in a way that hopefully minimizes pain, but Chromium developers are free to change the behavior of or remove flags at any time. In particular, just because a flag will expire through this process does not mean a developer will not remove it earlier than this process specifies.
The logic in //tools/flags/generate_unexpire_flags.py implements most of this. At any given time, if the current value of MAJOR in //chrome/version is $MSTONE, the two previous milestones ($MSTONE-1 and $MSTONE-2) are considered recent.
There are other elements of this process not described here, such as emails to flags-dev@ tracking the status of the process.
If a flag is no longer used (for instance, it was used to control a feature that has since launched), the flag should be removed. Delete the entry in about_flags.cc (and any corresponding entries for the flag description), and remove any references in flag-metadata.json.
In M78, the following flags are being hidden as the second step of this process. If you are using one of these flags for some reason, please get in touch with the flags team (via flags-dev@) and/or the listed owner(s) of that flag. This list will be updated at each milestone as we expire more flags. This is the authoritative source of the expiry set for a given milestone.
TODO(https://crbug.com/953690): Fill in this list :)