diff --git a/download/install/gammapy-1.3rc1-environment.yml b/download/install/gammapy-1.3rc1-environment.yml
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+# Conda environment for Gammapy version 1.3rc1
+# Install:    conda env create -f gammapy-1.3rc1-environment.yml
+# Activate:   conda activate gammapy-1.3rc1
+# Deactivate: conda deactivate
+
+name: gammapy-1.3rc1
+
+channels:
+  - conda-forge
+  - sherpa
+
+variables:
+  PYTHONNOUSERSITE: "1"
+
+dependencies:
+  - python=3.11
+  - gammapy=1.3rc1
+  - ipython=8.27
+  - cython
+  - jupyter
+  - jupyterlab=4.0
+  - pyyaml=6.0
+  - click=8.1
+  - numpy=1.26
+  - scipy=1.12
+  - pandas=2.2
+  - matplotlib=3.9
+  - astropy=6.0
+  - regions=0.8
+  - iminuit=2.24
+  - sherpa==4.17
+  - healpy=1.16
+  - naima=0.10
+  - pydantic=2.5
+  - emcee=3.1
+  - corner=2.2
+  - pip
+  - requests
+  - tqdm
+  - pip:
+    - ray[default]==2.35