diff --git a/pymc/backends/arviz.py b/pymc/backends/arviz.py
index 39553f6250..644225f7e2 100644
--- a/pymc/backends/arviz.py
+++ b/pymc/backends/arviz.py
@@ -582,8 +582,8 @@ def predictions_to_inference_data(
     )
     if hasattr(idata_orig, "posterior"):
         assert idata_orig is not None
-        converter.nchains = idata_orig["posterior"].dims["chain"]
-        converter.ndraws = idata_orig["posterior"].dims["draw"]
+        converter.nchains = idata_orig["posterior"].sizes["chain"]
+        converter.ndraws = idata_orig["posterior"].sizes["draw"]
     else:
         aelem = next(iter(predictions.values()))
         converter.nchains, converter.ndraws = aelem.shape[:2]
diff --git a/tests/backends/test_arviz.py b/tests/backends/test_arviz.py
index 4f6d312e29..f297c0eb57 100644
--- a/tests/backends/test_arviz.py
+++ b/tests/backends/test_arviz.py
@@ -156,8 +156,8 @@ def test_to_idata(self, data, eight_schools_params, chains, draws):
         }
         fails = check_multiple_attrs(test_dict, inference_data)
         assert not fails
-        chains = inference_data.posterior.dims["chain"]
-        draws = inference_data.posterior.dims["draw"]
+        chains = inference_data.posterior.sizes["chain"]
+        draws = inference_data.posterior.sizes["draw"]
         obs = inference_data.observed_data["obs"]
         assert inference_data.log_likelihood["obs"].shape == (chains, draws) + obs.shape
 
@@ -177,7 +177,7 @@ def test_predictions_to_idata(self, data, eight_schools_params):
         assert not fails
         for key, ivalues in inference_data.predictions.items():
             assert (
-                len(ivalues["chain"]) == inference_data.posterior.dims["chain"]
+                len(ivalues["chain"]) == inference_data.posterior.sizes["chain"]
             )  # same chains as in posterior
 
         # check adding in place
@@ -188,7 +188,7 @@ def test_predictions_to_idata(self, data, eight_schools_params):
         assert not fails
         for key, ivalues in inference_data.predictions.items():
             assert (
-                len(ivalues["chain"]) == inference_data.posterior.dims["chain"]
+                len(ivalues["chain"]) == inference_data.posterior.sizes["chain"]
             )  # same chains as in posterior
 
     def test_predictions_to_idata_new(self, data, eight_schools_params):
@@ -241,10 +241,10 @@ def test_posterior_predictive_thinned(self, data):
         }
         fails = check_multiple_attrs(test_dict, idata)
         assert not fails
-        assert idata.posterior.dims["chain"] == 2
-        assert idata.posterior.dims["draw"] == draws
-        assert idata.posterior_predictive.dims["chain"] == 2
-        assert idata.posterior_predictive.dims["draw"] == draws / thin_by
+        assert idata.posterior.sizes["chain"] == 2
+        assert idata.posterior.sizes["draw"] == draws
+        assert idata.posterior_predictive.sizes["chain"] == 2
+        assert idata.posterior_predictive.sizes["draw"] == draws / thin_by
         assert np.allclose(idata.posterior["draw"], np.arange(draws))
         assert np.allclose(idata.posterior_predictive["draw"], np.arange(draws, step=thin_by))
 
@@ -723,11 +723,11 @@ def test_save_warmup(self, save_warmup, chains, tune, draws):
         fails = check_multiple_attrs(test_dict, idata)
         assert not fails
         if hasattr(idata, "posterior"):
-            assert idata.posterior.dims["chain"] == chains
-            assert idata.posterior.dims["draw"] == draws
+            assert idata.posterior.sizes["chain"] == chains
+            assert idata.posterior.sizes["draw"] == draws
         if hasattr(idata, "warmup_posterior"):
-            assert idata.warmup_posterior.dims["chain"] == chains
-            assert idata.warmup_posterior.dims["draw"] == tune
+            assert idata.warmup_posterior.sizes["chain"] == chains
+            assert idata.warmup_posterior.sizes["draw"] == tune
 
     def test_save_warmup_issue_1208_after_3_9(self):
         with pm.Model():
@@ -757,8 +757,8 @@ def test_save_warmup_issue_1208_after_3_9(self):
             }
             fails = check_multiple_attrs(test_dict, idata)
             assert not fails
-            assert idata.posterior.dims["chain"] == 2
-            assert idata.posterior.dims["draw"] == 200
+            assert idata.posterior.sizes["chain"] == 2
+            assert idata.posterior.sizes["draw"] == 200
 
             # manually sliced trace triggers the same warning as <=3.8
             with pytest.warns(UserWarning, match="Warmup samples"):
@@ -771,5 +771,5 @@ def test_save_warmup_issue_1208_after_3_9(self):
             }
             fails = check_multiple_attrs(test_dict, idata)
             assert not fails
-            assert idata.posterior.dims["chain"] == 2
-            assert idata.posterior.dims["draw"] == 30
+            assert idata.posterior.sizes["chain"] == 2
+            assert idata.posterior.sizes["draw"] == 30
diff --git a/tests/sampling/test_jax.py b/tests/sampling/test_jax.py
index ed7c81fef8..8ec95552a0 100644
--- a/tests/sampling/test_jax.py
+++ b/tests/sampling/test_jax.py
@@ -433,8 +433,8 @@ def test_idata_contains_stats(sampler_name: str):
 
     stats = idata.get("sample_stats")
     assert stats is not None
-    n_chains = stats.dims["chain"]
-    n_draws = stats.dims["draw"]
+    n_chains = stats.sizes["chain"]
+    n_draws = stats.sizes["draw"]
 
     # Stats vars expected for both samplers
     expected_stat_vars = {
diff --git a/tests/smc/test_smc.py b/tests/smc/test_smc.py
index 81907739fe..e969b6a6e6 100644
--- a/tests/smc/test_smc.py
+++ b/tests/smc/test_smc.py
@@ -222,8 +222,8 @@ def test_return_datatype(self, chains):
 
         assert isinstance(idata, InferenceData)
         assert "sample_stats" in idata
-        assert idata.posterior.dims["chain"] == chains
-        assert idata.posterior.dims["draw"] == draws
+        assert idata.posterior.sizes["chain"] == chains
+        assert idata.posterior.sizes["draw"] == draws
 
         assert isinstance(mt, MultiTrace)
         assert mt.nchains == chains