diff --git a/.github/actions/install-mesa/action.yml b/.github/actions/install-mesa/action.yml
index 8cbe60e49..3f09fda82 100644
--- a/.github/actions/install-mesa/action.yml
+++ b/.github/actions/install-mesa/action.yml
@@ -7,7 +7,7 @@ inputs:
   sdk:
     description: 'The version of the MESA SDK to install'
     required: false
-    default: '26.3.2'
+    default: '26.6.1'
 
 
 
diff --git a/.github/actions/install-sdk-linux/action.yml b/.github/actions/install-sdk-linux/action.yml
index 52bdf5243..4b2a94831 100644
--- a/.github/actions/install-sdk-linux/action.yml
+++ b/.github/actions/install-sdk-linux/action.yml
@@ -30,7 +30,7 @@ runs:
       if: ${{ (steps.cache.outputs.cache-hit != 'true') }}
       run: |
         declare -A version
-        version[26.3.2]="https://zenodo.org/records/19210930"
+        version[26.6.1]="https://zenodo.org/records/20598423"
 
         curl -O ${version[${{inputs.sdk}}]}/files/mesasdk-x86_64-linux-${{inputs.sdk}}.tar.gz
 
diff --git a/.github/actions/install-sdk-macos/action.yml b/.github/actions/install-sdk-macos/action.yml
index 0ab062d49..b3475d9c0 100644
--- a/.github/actions/install-sdk-macos/action.yml
+++ b/.github/actions/install-sdk-macos/action.yml
@@ -28,9 +28,9 @@ runs:
       if: ${{ (steps.cache.outputs.cache-hit != 'true') }}
       run: |
         declare -A version
-        version[26.3.2]="https://zenodo.org/records/19210744/files"
+        version[26.6.1]="https://zenodo.org/records/20598224"
 
-        curl -O ${version[${{inputs.sdk}}]}/mesasdk-aarch64-macos-${{inputs.sdk}}.pkg
+        curl -O ${version[${{inputs.sdk}}]}/files/mesasdk-aarch64-macos-${{inputs.sdk}}.pkg
 
     - name: Unpack SDK
       run: |
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 6b7471b87..9e43f5c0f 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -14,7 +14,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        sdk: ["26.3.2"]  # pick 2 or 3 most recent.
+        sdk: ["26.6.1"]  # pick 2 or 3 most recent.
         os: [ubuntu-latest, macos-latest]
         dynamic: ["yes", "no"]
     runs-on: ${{ matrix.os }}
diff --git a/docs/source/changelog.rst b/docs/source/changelog.rst
index b8dc582e5..587b97564 100644
--- a/docs/source/changelog.rst
+++ b/docs/source/changelog.rst
@@ -35,6 +35,10 @@ Diffusive overshooting (overmixing) prescriptions now support a
 
 MESA no longer stops when reactions for which special rates are set are not in the nuclear network, only a warning is printed. This is intended to make it easier to test various network sizes without having to also change the list of special reactions.
 
+GYRE has been upgraded to 9.1.1, the most recent stable release. Changes since the previous release (8.1) included in MESA can be seen `here <https://github.com/rhdtownsend/gyre/releases>`__.
+
+The `MESA SDK <http://user.astro.wisc.edu/~townsend/static.php?ref=mesasdk>`__ recommended for compiling MESA has been updated to 26.6.1. Although this newer SDK is not required to successfully build MESA, it brings the benefit of restoring the cross-platform bit-for-bit compatibility that MESA once enjoyed (meaning that runs on Linux/Intel, MacOS/Intel and MacOS/ARM give identical results).
+
 .. _Bug Fixes main:
 
 Bug Fixes
@@ -48,7 +52,6 @@ The parameter ``report_max_infall_inside_fe_core`` was ignored in versions r25.1
 
 ``fe_core_infall_limit`` now obeys ``when_to_stop_rtol`` and ``when_to_stop_atol`` again (broken since r11532).
 
-
 .. note:: Before releasing a new version of MESA, move `Changes in main` to a new section below with the version number as the title, and add a new `Changes in main` section at the top of the file (see ``changelog_template.rst``).
 
 Changes in r26.4.1
diff --git a/gyre/Makefile b/gyre/Makefile
index 4d513e8fc..7fc992dd8 100644
--- a/gyre/Makefile
+++ b/gyre/Makefile
@@ -43,19 +43,14 @@ else
   GYRE_DEBUG = false
 endif
 
-ifeq ($(MESASDK_ROOT),)
-  FPP=./fypp_deps $(FLAGS_DEPS)
-else
-  FPP= PYTHONPATH=$(MESASDK_ROOT)/lib/python ./fypp_deps $(FLAGS_DEPS)
-endif
-
 BUILD_DIR_GYRE_BUILD := $(BUILD_DIR_MODULE)/src
 
-$(BUILD_DIR_GYRE_BUILD): gyre-8.1.tar.gz | $(BUILD_DIR_GYRE_BUILD)/. $(BUILD_DIR_MODULE)/include/.
+$(BUILD_DIR_GYRE_BUILD): gyre-9.1.1.tar.gz | $(BUILD_DIR_GYRE_BUILD)/. $(BUILD_DIR_MODULE)/include/.
 	tar --strip-components=1 -xf $< -C $(BUILD_DIR_GYRE_BUILD)
 
 $(BUILD_DIR_GYRE_BUILD)/build-complete: $(BUILD_DIR_GYRE_BUILD)
-	$(MAKE) -C $(BUILD_DIR_GYRE_BUILD) SHARED=$(DYNAMIC) DEBUG=$(GYRE_DEBUG) OMP=$(WITH_OPENMP) CRMATH=$(WITH_CRLIBM) VERSION_CHECK=passed FPP="$(FPP)" LDFLAGS="$(LIB_DEP_ARGS)" FFLAGS="$(_FFLAGS) -std=f2018" FRONTENDS=no TOOLS=no FORUM=no IFACES=yes
+	$(MAKE) -C $(BUILD_DIR_GYRE_BUILD) SHARED=$(DYNAMIC) DEBUG=$(GYRE_DEBUG) OMP=$(WITH_OPENMP) \
+            CRMATH=$(WITH_CRLIBM) FRONTENDS=no TOOLS=no EXTERNAL_FORUM=yes EXTERNAL_FORUM_PKG=mesa-forum IFACES=yes
 	touch $@
 
 
diff --git a/gyre/gyre-8.1.tar.gz b/gyre/gyre-8.1.tar.gz
deleted file mode 100644
index 1c3623161..000000000
--- a/gyre/gyre-8.1.tar.gz
+++ /dev/null
@@ -1,3 +0,0 @@
-version https://git-lfs.github.com/spec/v1
-oid sha256:c82f440ed952401c9a308555cc950fb770abc4b62957895ba546964e732d54f5
-size 4807156
diff --git a/gyre/gyre-9.1.1.tar.gz b/gyre/gyre-9.1.1.tar.gz
new file mode 100644
index 000000000..9d0f328ce
--- /dev/null
+++ b/gyre/gyre-9.1.1.tar.gz
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:7c6ece36c2565a3cfb266c961e276f914fead0ec6edef7b4a00b995bd0688a0b
+size 4850811