diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4493dd9c..2fa16bb6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,39 @@
 
 _None outstanding_
 
+# 4.0.0 / 2022-03-27
+
+_**Codename:** The "barely a release" release_
+
+This version contains a single - sadly breaking - change.
+
+- [#251](https://github.com/prometheus/client_ruby/pull/251) Remove framework-specific
+    route detection from collector middleware:
+    In 3.0.0 [we shipped](https://github.com/prometheus/client_ruby/issues/245) a feature
+    that attempted to use framework-specific information to determine the path of the
+    request in `Prometheus::Middleware::Collector`.
+
+    Sadly, we found out after shipping it that it was prone to multiple issues. We spent
+    a decent amount of time looking into them in depth, and came to the conclusion that
+    there wasn't any reasonable way to fix them - the issues are inherent to the feature.
+
+    For a full, detailed write-up of our investigation, see [this
+    comment](https://github.com/prometheus/client_ruby/issues/249#issuecomment-1061317511).
+
+    Almost all users will be unaffected by this change, but it is breaking per the
+    definition we've used for previous releases, so we've erred on the side of caution and
+    bumped the major version to communicate that.
+
+    If you use Sinatra or Grape with the `Prometheus::Middleware::Collector`, you will
+    notice different `path` labels being generated. If not, this release will change
+    nothing for you.
+
+    If you want the behaviour from 3.0.0 - or any custom path label generation you'd
+    prefer - we've updated [our collector middleware
+    documentation](https://github.com/prometheus/client_ruby/blob/master/examples/rack/README.md#collector).
+
+    **This may be a breaking change**. Labels may change in existing metrics.
+
 # 3.0.0 / 2022-02-05
 
 This new major version includes some breaking changes. They should be reasonably easy to
diff --git a/UPGRADING.md b/UPGRADING.md
index 75b1d0cc..8d065f21 100644
--- a/UPGRADING.md
+++ b/UPGRADING.md
@@ -1,3 +1,26 @@
+# Upgrading from 3.x.x to 4.x.x
+
+## Objectives
+
+4.0.0 contains a single breaking change - the [removal
+of](https://github.com/prometheus/client_ruby/pull/251) [framework-specific route
+detection](https://github.com/prometheus/client_ruby/pull/245) from
+`Prometheus::Middleware::Collector`.
+
+## Removal of framework-specific route detection
+
+In 3.0.0 we added a feature that used specific information provided by the Sinatra and
+Grape web frameworks to generate the `path` label in `Prometheus::Middleware::Collector`.
+
+This feature turned out to be inherently flawed, due to limitations in the information we
+can extract from the request environment. [This
+comment](https://github.com/prometheus/client_ruby/issues/249#issuecomment-1061317511)
+goes into much more depth on the investigation we did and the conclusions we came to.
+
+Most users will be unaffected by this change. If you use Sinatra or Grape and
+`Prometheus::Middleware::Collector` you will notice that your `path` label values will be
+much more similar to the ones we generated in the 2.x.x release series.
+
 # Upgrading from 2.x.x to 3.x.x
 
 ## Objectives
diff --git a/lib/prometheus/client/version.rb b/lib/prometheus/client/version.rb
index 75b09338..4f22986c 100644
--- a/lib/prometheus/client/version.rb
+++ b/lib/prometheus/client/version.rb
@@ -2,6 +2,6 @@
 
 module Prometheus
   module Client
-    VERSION = '3.0.0'
+    VERSION = '4.0.0'
   end
 end