diff --git a/.github/workflows/full-stack.yaml b/.github/workflows/full-stack.yaml
index 9cefc8f..f2fce67 100644
--- a/.github/workflows/full-stack.yaml
+++ b/.github/workflows/full-stack.yaml
@@ -38,6 +38,7 @@ jobs:
       uses: actions/checkout@v7
       with:
         repository: openforcefield/openff-interchange
+        ref: "fix-pydantic"
         path: openff-interchange
 
     - name: Checkout QCSubmit
@@ -58,6 +59,7 @@ jobs:
       uses: actions/checkout@v7
       with:
         repository: openforcefield/openff-units
+        ref: "define-pydantic-schema"
         path: openff-units
 
     - name: Checkout OpenFF Utilities
diff --git a/devtools/conda-envs/full-stack.yaml b/devtools/conda-envs/full-stack.yaml
index a4d8b87..3294e80 100644
--- a/devtools/conda-envs/full-stack.yaml
+++ b/devtools/conda-envs/full-stack.yaml
@@ -1,13 +1,13 @@
 name: full-stack-tests
 channels:
-  - openeye
+  - conda-forge/label/openff-interchange-dev
   - conda-forge
 dependencies:
   - python
   - setuptools =81
   - pip
   - numpy >=2.4
-  - pydantic =2.11.10
+  - pydantic >=2.12
   - pint >=0.25
   - openff-toolkit >=0.18
   - ambertools =24.8  # just to help solver
@@ -24,7 +24,7 @@ dependencies:
   - toml
   - bson
   - msgpack-python
-  - openeye-toolkits >=2025
+  - openeye::openeye-toolkits >=2025
   - rdkit >=2025.09.5
   - intermol
 
@@ -50,3 +50,7 @@ dependencies:
   - openmpi =4
 
   - icu=75 # just to help solver
+
+  - pip:
+    - git+https://github.com/openforcefield/openff-units.git@define-pydantic-schema
+    - git+https://github.com/openforcefield/openff-interchange.git@fix-pydantic