diff --git a/.github/workflows/dafny_interop_test_net.yml b/.github/workflows/dafny_interop_test_net.yml
index fd56e893e..8126a27e1 100644
--- a/.github/workflows/dafny_interop_test_net.yml
+++ b/.github/workflows/dafny_interop_test_net.yml
@@ -37,7 +37,7 @@ jobs:
         os: [
           windows-latest,
           ubuntu-latest,
-          macos-12,
+          macos-15,
         ]
     runs-on: ${{ matrix.os }}
     permissions:
diff --git a/.github/workflows/dafny_interop_test_vector_net.yml b/.github/workflows/dafny_interop_test_vector_net.yml
index 2940a1a67..9aeef22c9 100644
--- a/.github/workflows/dafny_interop_test_vector_net.yml
+++ b/.github/workflows/dafny_interop_test_vector_net.yml
@@ -36,7 +36,7 @@ jobs:
         os: [
           windows-latest,
           ubuntu-latest,
-          macos-12,
+          macos-15,
         ]
     runs-on: ${{matrix.os}}
     permissions:
@@ -146,7 +146,7 @@ jobs:
       matrix:
         os: [
           ubuntu-latest,
-          macos-12,
+          macos-15,
         ]
     runs-on: ${{ matrix.os }}
     permissions:
@@ -251,7 +251,7 @@ jobs:
       matrix:
         os: [
           ubuntu-latest,
-          macos-12,
+          macos-15,
         ]
     runs-on: ${{ matrix.os }}
     permissions:
diff --git a/.github/workflows/library_dafny_verification.yml b/.github/workflows/library_dafny_verification.yml
index f36a30347..944eda849 100644
--- a/.github/workflows/library_dafny_verification.yml
+++ b/.github/workflows/library_dafny_verification.yml
@@ -21,7 +21,7 @@ jobs:
         library: [
           AwsEncryptionSDK
         ]
-        os: [ macos-12 ]
+        os: [ macos-15 ]
     runs-on: ${{ matrix.os }}
     env:
       DOTNET_CLI_TELEMETRY_OPTOUT: 1
diff --git a/.github/workflows/library_interop_tests.yml b/.github/workflows/library_interop_tests.yml
index 112b6825a..aef6e4b1f 100644
--- a/.github/workflows/library_interop_tests.yml
+++ b/.github/workflows/library_interop_tests.yml
@@ -27,7 +27,7 @@ jobs:
         os: [
           windows-latest,
           ubuntu-latest,
-          macos-12,
+          macos-15,
         ]
     runs-on: ${{ matrix.os }}
     permissions:
@@ -125,7 +125,7 @@ jobs:
       matrix:
         os: [
           ubuntu-latest,
-          macos-12,
+          macos-15,
         ]
     runs-on: ${{ matrix.os }}
     permissions:
@@ -230,7 +230,7 @@ jobs:
       matrix:
         os: [
           ubuntu-latest,
-          macos-12,
+          macos-15,
         ]
     runs-on: ${{ matrix.os }}
     permissions:
diff --git a/.github/workflows/library_java_tests.yml b/.github/workflows/library_java_tests.yml
index 101a6223a..cc6f44cf2 100644
--- a/.github/workflows/library_java_tests.yml
+++ b/.github/workflows/library_java_tests.yml
@@ -25,7 +25,7 @@ jobs:
           # TODO just test on mac for now
           #windows-latest,
           #ubuntu-latest,
-          macos-12
+          macos-15
         ]
     runs-on: ${{ matrix.os }}
     permissions:
diff --git a/.github/workflows/library_net_tests.yml b/.github/workflows/library_net_tests.yml
index 910f5200f..0da0aec83 100644
--- a/.github/workflows/library_net_tests.yml
+++ b/.github/workflows/library_net_tests.yml
@@ -33,7 +33,7 @@ jobs:
         os: [
           windows-latest,
           ubuntu-latest,
-          macos-12,
+          macos-15,
         ]
     runs-on: ${{ matrix.os }}
     permissions:
diff --git a/.github/workflows/pull.yml b/.github/workflows/pull.yml
index 655eea31c..c3f63bad2 100644
--- a/.github/workflows/pull.yml
+++ b/.github/workflows/pull.yml
@@ -8,11 +8,11 @@ jobs:
   pr-ci-codegen:
     uses: ./.github/workflows/library_codegen.yml
     with:
-      dafny: '4.8.0'
+      dafny: '4.9.0'
   pr-ci-verification:
     uses: ./.github/workflows/library_dafny_verification.yml
     with:
-      dafny: '4.8.0'
+      dafny: '4.9.0'
   # pr-ci-java:
   #   uses: ./.github/workflows/library_java_tests.yml
   #   with:
@@ -20,8 +20,8 @@ jobs:
   pr-ci-net:
     uses: ./.github/workflows/library_net_tests.yml
     with:
-      dafny: '4.8.0'
+      dafny: '4.9.0'
   pr-test-vectors:
     uses: ./.github/workflows/library_interop_tests.yml
     with:
-      dafny: '4.8.0'
+      dafny: '4.9.0'
diff --git a/.github/workflows/sem_ver.yml b/.github/workflows/sem_ver.yml
index 1acf295f9..0581a358f 100644
--- a/.github/workflows/sem_ver.yml
+++ b/.github/workflows/sem_ver.yml
@@ -6,7 +6,7 @@ on:
 
 jobs:
   semantic-release:
-    runs-on: macos-12
+    runs-on: macos-15
     permissions:
       id-token: write
       contents: read
diff --git a/.github/workflows/semantic_release.yml b/.github/workflows/semantic_release.yml
index 5fb0fd0f6..4dd095956 100644
--- a/.github/workflows/semantic_release.yml
+++ b/.github/workflows/semantic_release.yml
@@ -15,7 +15,7 @@ jobs:
     # privileged operation, so we must make sure this list of users is a subset of the users labeled as maintainers of
     # https://github.com/orgs/aws/teams/aws-crypto-tools
     if: contains('["seebees","texastony","ShubhamChaturvedi7","lucasmcdonald3","josecorella","imabhichow","rishav-karanjit","antonf-amzn","justplaz","ajewellamz","RitvikKapila"]', github.actor)
-    runs-on: macos-12
+    runs-on: macos-15
     permissions:
       id-token: write
       contents: write
diff --git a/AwsEncryptionSDK/dafny/AwsEncryptionSdk/test/Fixtures.dfy b/AwsEncryptionSDK/dafny/AwsEncryptionSdk/test/Fixtures.dfy
index a7d7d5652..f73045a5a 100644
--- a/AwsEncryptionSDK/dafny/AwsEncryptionSdk/test/Fixtures.dfy
+++ b/AwsEncryptionSDK/dafny/AwsEncryptionSdk/test/Fixtures.dfy
@@ -20,7 +20,7 @@ module Fixtures {
   
   const branchKeyStoreName := "KeyStoreDdbTable"
   const logicalKeyStoreName := branchKeyStoreName
-  const branchKeyId := "75789115-1deb-4fe3-a2ec-be9e885d1945"
+  const branchKeyId := "3f43a9af-08c5-4317-b694-3d3e883dcaef"
   
   // UTF-8 encoded "aws-crypto-"
   const RESERVED_ENCRYPTION_CONTEXT: UTF8.ValidUTF8Bytes :=
diff --git a/AwsEncryptionSDK/project.properties b/AwsEncryptionSDK/project.properties
index f5e8cdf0b..55d988fe1 100644
--- a/AwsEncryptionSDK/project.properties
+++ b/AwsEncryptionSDK/project.properties
@@ -1,4 +1,4 @@
 # This file stores the top level dafny version information.
 # All elements of the project need to agree on this version.
-dafnyVersion=4.8.1
-dafnyRuntimeJavaVersion=4.8.1
+dafnyVersion=4.9.0
+dafnyRuntimeJavaVersion=4.9.0
diff --git a/AwsEncryptionSDK/runtimes/net/CHANGELOG.md b/AwsEncryptionSDK/runtimes/net/CHANGELOG.md
index bf9b9eb6a..da1d67eb2 100644
--- a/AwsEncryptionSDK/runtimes/net/CHANGELOG.md
+++ b/AwsEncryptionSDK/runtimes/net/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Changelog
 
+## 4.1.1
+
+### Notes
+
+Update .csproj files to prevent use of AWS-SDK-NET V4
+
 ## 4.1.0
 
 ### Notes
diff --git a/AwsEncryptionSDK/runtimes/net/ESDK.csproj b/AwsEncryptionSDK/runtimes/net/ESDK.csproj
index c2abb450e..81cf2982e 100644
--- a/AwsEncryptionSDK/runtimes/net/ESDK.csproj
+++ b/AwsEncryptionSDK/runtimes/net/ESDK.csproj
@@ -8,7 +8,7 @@
       <EnableDefaultCompileItems>false</EnableDefaultCompileItems>
       <IsPackable>true</IsPackable>
       
-      <Version>4.1.0</Version>
+      <Version>4.1.1</Version>
 
       <AssemblyName>AWS.Cryptography.EncryptionSDK</AssemblyName>
       <PackageId>AWS.Cryptography.EncryptionSDK</PackageId>
@@ -30,10 +30,8 @@
 
   <ItemGroup>
       <!-- TODO: manually upgraded to match the latest from MPL, is that reasonable? -->
-      <PackageReference Include="AWSSDK.Core" Version="3.7.*" />
-      <PackageReference Include="DafnyRuntime" Version="4.8.0" />
-      <PackageReference Include="BouncyCastle.Cryptography" Version="2.3.1" />
-      <ProjectReference Include="../../../mpl/AwsCryptographicMaterialProviders/runtimes/net/MPL.csproj" />
+      <PackageReference Include="DafnyRuntime" Version="[4.9.0]" />
+      <PackageReference Include="AWS.Cryptography.MaterialProviders" Version="[1.7.6]" />
       <!--
         System.Collections.Immutable can be removed once dafny.msbuild is updated with
         https://github.com/dafny-lang/dafny.msbuild/pull/10 and versioned
diff --git a/mpl b/mpl
index 71cf95396..1f2351f1c 160000
--- a/mpl
+++ b/mpl
@@ -1 +1 @@
-Subproject commit 71cf95396fe3b053960c65f36dfc9def614e295b
+Subproject commit 1f2351f1c8908f1153d9c3dda31317c0f379a0fc