diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index dfd3b23ee..afd4719ad 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -17,10 +17,6 @@ jobs:
         cabal:
           - "latest"
         ghc:
-          - "8.10.7"
-          - "9.0.2"
-          - "9.2.8"
-          - "9.4.8"
           - "9.6.6"
           - "9.8.2"
           - "9.10.3"
@@ -64,13 +60,10 @@ jobs:
         # ghc must match each snapshot's compiler exactly, since we build
         # with --system-ghc against the GHC provisioned by the setup action.
         plan:
-          - { resolver: "--stack-yaml ./stack-8.10.yaml", ghc: "8.10.7" }
-          - { resolver: "--stack-yaml ./stack-9.0.yaml",  ghc: "9.0.2" }
-          - { resolver: "--stack-yaml ./stack-9.2.yaml",  ghc: "9.2.8" }
-          - { resolver: "--stack-yaml ./stack-9.4.yaml",  ghc: "9.4.8" }
           - { resolver: "--stack-yaml ./stack-9.6.yaml",  ghc: "9.6.6" }
           - { resolver: "--stack-yaml ./stack-9.8.yaml",  ghc: "9.8.4" }
           - { resolver: "--stack-yaml ./stack-9.10.yaml", ghc: "9.10.3" }
+          - { resolver: "--stack-yaml ./stack-9.12.yaml", ghc: "9.12.4" }
 
     steps:
     - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
diff --git a/.hgignore b/.hgignore
deleted file mode 100644
index 427cb183d..000000000
--- a/.hgignore
+++ /dev/null
@@ -1,11 +0,0 @@
-syntax: regexp
-~$
-\#.*\#$
-\.\#
-\.DS_Store$
-\.cabal-sandbox/
-\.hpc/
-\.tix$
-cabal\.sandbox\.config$
-dist/
-\.stack-work/
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index d2e276380..000000000
--- a/.travis.yml
+++ /dev/null
@@ -1,32 +0,0 @@
-sudo: required
-
-os: linux
-dist: xenial
-
-env:
- - GHCVER=8.0.2
- - GHCVER=8.2.2
- - GHCVER=8.4.4
- - GHCVER=8.6.5
-
-cache:
-  directories:
-  - $HOME/.ghc
-  - $HOME/.cabal
-
-before_install:
- - sudo add-apt-repository -y ppa:hvr/ghc
- - sudo apt-get update
- - sudo apt-get install alex-3.1.7 happy-1.19.5 cabal-install-3.0 ghc-$GHCVER
- - export PATH=/opt/cabal/bin:/opt/ghc/$GHCVER/bin:/opt/alex/3.1.7/bin:/opt/happy/1.19.5/bin:$PATH
-
-install:
- - cabal-3.0 update
-
-script:
- - cabal-3.0 configure --enable-tests
- - cabal-3.0 build
- - cabal-3.0 test --test-show-details=streaming
- - cabal-3.0 check
- - cabal-3.0 haddock
- - cabal-3.0 sdist
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 57954c745..ff1d8914d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,9 @@
 
+## Unreleased
+
+*   Raise the minimum supported GHC to 9.6 (`base >= 4.18`). Older compilers
+    are no longer tested in CI.
+
 ## 2.4.0
 
 *   Add a `reset` function to the
diff --git a/prometheus.cabal b/prometheus.cabal
index db57a7874..d48d4ac66 100644
--- a/prometheus.cabal
+++ b/prometheus.cabal
@@ -10,6 +10,7 @@ maintainer:          luke@bitnomial.com, opensource@bitnomial.com
 copyright:           Bitnomial, Inc. (c) 2016-2023
 category:            Metrics, Monitoring, Web, System
 build-type:          Simple
+tested-with:         GHC == 9.6.6, GHC == 9.8.2, GHC == 9.8.4, GHC == 9.10.3, GHC == 9.12.4
 cabal-version:       >=1.10
 
 description:
@@ -88,7 +89,7 @@ library
                  , System.Metrics.Prometheus.Registry
                  , System.Metrics.Prometheus.RegistryT
 
-  build-depends: base            >= 4.9  && < 5
+  build-depends: base            >= 4.18 && < 5
                , atomic-primops  >= 0.8  && < 0.9
                , bytestring      >= 0.10 && < 0.13
                , containers      >= 0.5  && < 0.8
diff --git a/src/System/Metrics/Prometheus/Concurrent/Registry.hs b/src/System/Metrics/Prometheus/Concurrent/Registry.hs
index 123791433..6f1e69ab3 100644
--- a/src/System/Metrics/Prometheus/Concurrent/Registry.hs
+++ b/src/System/Metrics/Prometheus/Concurrent/Registry.hs
@@ -9,7 +9,6 @@ module System.Metrics.Prometheus.Concurrent.Registry (
     sample,
 ) where
 
-import Control.Applicative ((<$>))
 import Control.Concurrent.MVar (
     MVar,
     modifyMVarMasked,
diff --git a/src/System/Metrics/Prometheus/Concurrent/RegistryT.hs b/src/System/Metrics/Prometheus/Concurrent/RegistryT.hs
index 3b2b9208f..446fa8a5c 100644
--- a/src/System/Metrics/Prometheus/Concurrent/RegistryT.hs
+++ b/src/System/Metrics/Prometheus/Concurrent/RegistryT.hs
@@ -2,7 +2,6 @@
 
 module System.Metrics.Prometheus.Concurrent.RegistryT where
 
-import Control.Applicative ((<$>))
 import Control.Monad.IO.Class (MonadIO, liftIO)
 import Control.Monad.Trans.Class (MonadTrans)
 import Control.Monad.Trans.Reader (
diff --git a/src/System/Metrics/Prometheus/Encode/Text.hs b/src/System/Metrics/Prometheus/Encode/Text.hs
index f18a5d3b7..4b1f36055 100644
--- a/src/System/Metrics/Prometheus/Encode/Text.hs
+++ b/src/System/Metrics/Prometheus/Encode/Text.hs
@@ -9,7 +9,6 @@ import Data.List (
     intersperse,
  )
 import qualified Data.Map as Map
-import Data.Monoid ((<>))
 
 import System.Metrics.Prometheus.Encode.Text.Histogram (encodeHistogram)
 import System.Metrics.Prometheus.Encode.Text.MetricId (
diff --git a/src/System/Metrics/Prometheus/Encode/Text/Histogram.hs b/src/System/Metrics/Prometheus/Encode/Text/Histogram.hs
index 97889b2fe..943841c71 100644
--- a/src/System/Metrics/Prometheus/Encode/Text/Histogram.hs
+++ b/src/System/Metrics/Prometheus/Encode/Text/Histogram.hs
@@ -7,7 +7,6 @@ module System.Metrics.Prometheus.Encode.Text.Histogram (
 import Data.ByteString.Builder (Builder)
 import Data.List (intersperse)
 import qualified Data.Map as Map
-import Data.Monoid ((<>))
 
 import System.Metrics.Prometheus.Encode.Text.MetricId (
     encodeDouble,
diff --git a/src/System/Metrics/Prometheus/Encode/Text/MetricId.hs b/src/System/Metrics/Prometheus/Encode/Text/MetricId.hs
index 7b6326e7b..f7ea06fcc 100644
--- a/src/System/Metrics/Prometheus/Encode/Text/MetricId.hs
+++ b/src/System/Metrics/Prometheus/Encode/Text/MetricId.hs
@@ -20,7 +20,6 @@ import Data.ByteString.Builder (
     intDec,
  )
 import Data.List (intersperse)
-import Data.Monoid ((<>))
 import Data.Text (Text, replace)
 import Data.Text.Encoding (encodeUtf8)
 import Data.Text.Lazy (toStrict)
diff --git a/src/System/Metrics/Prometheus/Http/Scrape.hs b/src/System/Metrics/Prometheus/Http/Scrape.hs
index be1bf7686..a6a1790bc 100644
--- a/src/System/Metrics/Prometheus/Http/Scrape.hs
+++ b/src/System/Metrics/Prometheus/Http/Scrape.hs
@@ -7,7 +7,6 @@ module System.Metrics.Prometheus.Http.Scrape (
     prometheusApp,
 ) where
 
-import Control.Applicative ((<$>))
 import Control.Monad.IO.Class (
     MonadIO,
     liftIO,
diff --git a/src/System/Metrics/Prometheus/Metric/Counter.hs b/src/System/Metrics/Prometheus/Metric/Counter.hs
index 70d8148f4..2800a72a8 100644
--- a/src/System/Metrics/Prometheus/Metric/Counter.hs
+++ b/src/System/Metrics/Prometheus/Metric/Counter.hs
@@ -9,7 +9,6 @@ module System.Metrics.Prometheus.Metric.Counter (
     set,
 ) where
 
-import Control.Applicative ((<$>))
 import Control.Monad (when)
 import Data.Atomics.Counter (AtomicCounter, incrCounter, newCounter, writeCounter)
 
diff --git a/src/System/Metrics/Prometheus/Metric/Gauge.hs b/src/System/Metrics/Prometheus/Metric/Gauge.hs
index 3c0852e2c..fdea3080e 100644
--- a/src/System/Metrics/Prometheus/Metric/Gauge.hs
+++ b/src/System/Metrics/Prometheus/Metric/Gauge.hs
@@ -11,7 +11,6 @@ module System.Metrics.Prometheus.Metric.Gauge (
     modifyAndSample,
 ) where
 
-import Control.Applicative ((<$>))
 import Data.IORef (IORef, atomicModifyIORef', newIORef)
 
 
diff --git a/src/System/Metrics/Prometheus/Metric/Histogram.hs b/src/System/Metrics/Prometheus/Metric/Histogram.hs
index d1db1649f..4e227dab2 100644
--- a/src/System/Metrics/Prometheus/Metric/Histogram.hs
+++ b/src/System/Metrics/Prometheus/Metric/Histogram.hs
@@ -12,7 +12,6 @@ module System.Metrics.Prometheus.Metric.Histogram (
     reset,
 ) where
 
-import Control.Applicative ((<$>))
 import Control.Monad (void)
 import Data.Bool (bool)
 import Data.IORef (
diff --git a/src/System/Metrics/Prometheus/MetricId.hs b/src/System/Metrics/Prometheus/MetricId.hs
index 58d2c9438..0df301b86 100644
--- a/src/System/Metrics/Prometheus/MetricId.hs
+++ b/src/System/Metrics/Prometheus/MetricId.hs
@@ -7,8 +7,6 @@ import Data.Bifunctor (first)
 import Data.Char (isDigit)
 import Data.Map (Map)
 import qualified Data.Map as Map
-import Data.Monoid (Monoid)
-import Data.Semigroup (Semigroup)
 import Data.String (IsString (..))
 import Data.Text (Text)
 import qualified Data.Text as Text
diff --git a/src/System/Metrics/Prometheus/Registry.hs b/src/System/Metrics/Prometheus/Registry.hs
index b39a5899b..17438c889 100644
--- a/src/System/Metrics/Prometheus/Registry.hs
+++ b/src/System/Metrics/Prometheus/Registry.hs
@@ -1,5 +1,3 @@
-{-# LANGUAGE DeriveDataTypeable #-}
-
 module System.Metrics.Prometheus.Registry (
     Registry,
     RegistrySample (..),
@@ -12,11 +10,9 @@ module System.Metrics.Prometheus.Registry (
     sample,
 ) where
 
-import Control.Applicative ((<$>))
 import Control.Exception (Exception, throw)
 import Data.Map (Map)
 import qualified Data.Map as Map
-import Data.Typeable (Typeable)
 
 import System.Metrics.Prometheus.Metric (
     Metric (..),
@@ -42,7 +38,7 @@ newtype Registry = Registry {unRegistry :: Map MetricId Metric}
 newtype RegistrySample = RegistrySample {unRegistrySample :: Map MetricId MetricSample}
 
 
-newtype KeyError = KeyError MetricId deriving (Show, Typeable)
+newtype KeyError = KeyError MetricId deriving (Show)
 instance Exception KeyError
 
 
diff --git a/src/System/Metrics/Prometheus/RegistryT.hs b/src/System/Metrics/Prometheus/RegistryT.hs
index 5f34cbe5c..da93d72b7 100644
--- a/src/System/Metrics/Prometheus/RegistryT.hs
+++ b/src/System/Metrics/Prometheus/RegistryT.hs
@@ -2,7 +2,6 @@
 
 module System.Metrics.Prometheus.RegistryT where
 
-import Control.Applicative ((<$>))
 import Control.Monad.IO.Class (MonadIO, liftIO)
 import Control.Monad.Trans.Class (MonadTrans)
 import Control.Monad.Trans.State.Strict (
diff --git a/stack-8.10.yaml b/stack-8.10.yaml
deleted file mode 100644
index 68e5260b0..000000000
--- a/stack-8.10.yaml
+++ /dev/null
@@ -1,6 +0,0 @@
----
-resolver: lts-18.28
-flags: {}
-packages:
-  - '.'
-extra-deps: []
diff --git a/stack-9.0.yaml b/stack-9.0.yaml
deleted file mode 100644
index 3be543604..000000000
--- a/stack-9.0.yaml
+++ /dev/null
@@ -1,6 +0,0 @@
----
-resolver: lts-19.33
-flags: {}
-packages:
-  - "."
-extra-deps: []
diff --git a/stack-9.2.yaml b/stack-9.12.yaml
similarity index 61%
rename from stack-9.2.yaml
rename to stack-9.12.yaml
index 287d01ca2..b17394ba9 100644
--- a/stack-9.2.yaml
+++ b/stack-9.12.yaml
@@ -1,5 +1,5 @@
 ---
-resolver: lts-20.26
+resolver: nightly-2026-10-09
 flags: {}
 packages:
   - "."
diff --git a/stack-9.4.yaml b/stack-9.4.yaml
deleted file mode 100644
index 58ac959cd..000000000
--- a/stack-9.4.yaml
+++ /dev/null
@@ -1,6 +0,0 @@
----
-resolver: lts-21.25
-flags: {}
-packages:
-  - "."
-extra-deps: []