diff --git a/base.cabal b/base.cabal
--- a/base.cabal
+++ b/base.cabal
@@ -4,7 +4,7 @@
 -- Make sure you are editing ghc-experimental.cabal.in, not ghc-experimental.cabal
 
 name:           base
-version:        4.21.1.0
+version:        4.21.2.0
 -- NOTE: Don't forget to update ./changelog.md
 
 license:        BSD-3-Clause
@@ -30,7 +30,7 @@
     default-language: Haskell2010
     default-extensions: NoImplicitPrelude
     build-depends:
-        ghc-internal == 9.1203.*,
+        ghc-internal == 9.1204.*,
         ghc-prim,
 
     exposed-modules:
diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,5 +1,10 @@
 # Changelog for [`base` package](http://hackage.haskell.org/package/base)
 
+## 4.21.2.0 *March 2026*
+  * Expose `Backtraces` constructor and fields ([CLC proposal #199](https://github.com/haskell/core-libraries-committee/issues/199), [#26049](https://gitlab.haskell.org/ghc/ghc/-/issues/26049))
+  * Store `StackTrace` and `StackSnapshot` in `Backtraces`, deferring decoding until display
+  * Evaluate backtraces for "error" exceptions at the moment they are thrown ([CLC proposal #383](https://github.com/haskell/core-libraries-committee/issues/383), [#26751](https://gitlab.haskell.org/ghc/ghc/-/issues/26751))
+
 ## 4.21.1.0 *Sept 2024*
   * Fix incorrect results of `integerPowMod` when the base is 0 and the exponent is negative, and `integerRecipMod` when the modulus is zero ([#26017](https://gitlab.haskell.org/ghc/ghc/-/issues/26017)).
   * Fix bug where `naturalAndNot` was incorrectly truncating results ([CLC proposal #350](github.com/haskell/core-libraries-committee/issues/350))
diff --git a/src/Control/Exception/Backtrace.hs b/src/Control/Exception/Backtrace.hs
--- a/src/Control/Exception/Backtrace.hs
+++ b/src/Control/Exception/Backtrace.hs
@@ -51,7 +51,7 @@
     , getBacktraceMechanismState
     , setBacktraceMechanismState
       -- * Collecting backtraces
-    , Backtraces
+    , Backtraces(..)
     , displayBacktraces
     , collectBacktraces
     ) where
diff --git a/src/System/Info.hs b/src/System/Info.hs
--- a/src/System/Info.hs
+++ b/src/System/Info.hs
@@ -42,6 +42,8 @@
 -- | The full version of 'compilerName' with which the program was compiled
 -- or is being interpreted. It includes the major, minor, revision and an additional
 -- identifier, generally in the form "<year><month><day>".
+--
+-- @since 4.15.0.0
 fullCompilerVersion :: Version
 fullCompilerVersion = Version version []
   where