diff --git a/deepspeed/ops/transformer/inference/op_binding/softmax_context.py b/deepspeed/ops/transformer/inference/op_binding/softmax_context.py
index d745df678e93..a199f49d8528 100644
--- a/deepspeed/ops/transformer/inference/op_binding/softmax_context.py
+++ b/deepspeed/ops/transformer/inference/op_binding/softmax_context.py
@@ -80,8 +80,16 @@ def softmax_context_fallback(self, query_key_value, attn_mask, rotary_dim, rotat
             from transformers.models.llama.modeling_llama import apply_rotary_pos_emb
 
             rotary = InferenceContext.Instance().get_rotary(rotary_dim, rope_theta, bat_0213_value.device)
-            cos, sin = rotary(bat_0213_value, InferenceContext.Instance().get_max_tokens_num())
-            bat_0213_query, bat_0213_key = apply_rotary_pos_emb(bat_0213_query, bat_0213_key, cos, sin, position_ids)
+            # LlamaRotaryEmbedding.forward takes position_ids, not a token count.
+            cos, sin = rotary(bat_0213_value, position_ids)
+            # apply_rotary_pos_emb takes them only through cos/sin. transformers 5.0
+            # dropped the deprecated position_ids parameter, so the fifth positional
+            # slot is unsqueeze_dim there:
+            #   4.51.3 .. 4.57.0   (q, k, cos, sin, position_ids=None, unsqueeze_dim=1)
+            #   5.0.0  .. 5.16.1   (q, k, cos, sin, unsqueeze_dim=1)
+            # Passing four arguments is correct on both, and leaves unsqueeze_dim at its
+            # default rather than handing it a tensor.
+            bat_0213_query, bat_0213_key = apply_rotary_pos_emb(bat_0213_query, bat_0213_key, cos, sin)
 
         bat_0213_key, bat_0213_value = InferenceContext.Instance().update_cache(layer_id, token_idx, is_prompt,
                                                                                 bat_0213_key, bat_0213_value)
diff --git a/deepspeed/ops/transformer/inference/op_binding/workspace.py b/deepspeed/ops/transformer/inference/op_binding/workspace.py
index 0565666559bf..efd9104a57b4 100644
--- a/deepspeed/ops/transformer/inference/op_binding/workspace.py
+++ b/deepspeed/ops/transformer/inference/op_binding/workspace.py
@@ -137,9 +137,17 @@ def get_kv_cache(self):
 
     def get_rotary(self, rotary_dim, rope_theta, device=None):
         if self.rotary is None:
+            from transformers.models.llama.configuration_llama import LlamaConfig
             from transformers.models.llama.modeling_llama import LlamaRotaryEmbedding
 
-            self.rotary = LlamaRotaryEmbedding(rotary_dim, base=rope_theta, device=device)
+            # transformers 4.48 replaced the (dim, base=..., device=...) signature with one
+            # that reads both off a config. head_dim carries the rotary width and rope_theta
+            # the base; transformers 5 folds rope_theta into rope_parameters itself, so
+            # passing it this way works on both.
+            config = LlamaConfig(head_dim=rotary_dim, rope_theta=rope_theta)
+            self.rotary = LlamaRotaryEmbedding(config)
+            if device is not None:
+                self.rotary = self.rotary.to(device)
 
         return self.rotary
 
diff --git a/tests/unit/ops/transformer/inference/test_rotary_embedding.py b/tests/unit/ops/transformer/inference/test_rotary_embedding.py
new file mode 100644
index 000000000000..f728e60fabfd
--- /dev/null
+++ b/tests/unit/ops/transformer/inference/test_rotary_embedding.py
@@ -0,0 +1,112 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0
+
+# DeepSpeed Team
+"""InferenceContext.get_rotary has to build a rotary embedding the installed transformers accepts.
+
+transformers 4.48 replaced `LlamaRotaryEmbedding(dim, base=..., device=...)` with a
+config-taking constructor, and its forward went from a token count to `position_ids`. The
+fallback attention path in `softmax_context.py` used both of the old shapes, so it raised
+`TypeError: __init__() got an unexpected keyword argument 'base'` before reaching any kernel.
+
+No accelerator needed: this covers the construction and the rope values, and the rest of the
+fallback path is unchanged.
+"""
+
+import pytest
+import torch
+
+from deepspeed.ops.transformer.inference.config import DeepSpeedInferenceConfig
+from deepspeed.ops.transformer.inference.op_binding.softmax_context import SoftmaxContextOp
+from deepspeed.ops.transformer.inference.op_binding.workspace import InferenceContext
+
+
+def _reference_cos_sin(rotary_dim, rope_theta, seq_len):
+    """cos/sin straight from the rope definition, independent of transformers."""
+    inv_freq = 1.0 / (rope_theta**(torch.arange(0, rotary_dim, 2).float() / rotary_dim))
+    freqs = torch.outer(torch.arange(seq_len).float(), inv_freq)
+    emb = torch.cat((freqs, freqs), dim=-1)
+    return emb.cos(), emb.sin()
+
+
+@pytest.fixture
+def context():
+    ctx = InferenceContext.Instance()
+    ctx.rotary = None
+    yield ctx
+    ctx.rotary = None
+
+
+@pytest.mark.parametrize("rotary_dim", [32, 64, 128])
+@pytest.mark.parametrize("rope_theta", [10000.0, 500000.0])
+def test_get_rotary_matches_the_rope_definition(context, rotary_dim, rope_theta):
+    seq_len = 12
+    rotary = context.get_rotary(rotary_dim, rope_theta)
+
+    position_ids = torch.arange(seq_len).unsqueeze(0)
+    cos, sin = rotary(torch.zeros(1, 1, seq_len, rotary_dim), position_ids)
+
+    expected_cos, expected_sin = _reference_cos_sin(rotary_dim, rope_theta, seq_len)
+    assert cos.shape == (1, seq_len, rotary_dim)
+    torch.testing.assert_close(cos[0], expected_cos)
+    torch.testing.assert_close(sin[0], expected_sin)
+
+
+def test_get_rotary_uses_rotary_dim_not_the_config_default(context):
+    """rotary_dim has to reach the embedding, not the LlamaConfig hidden_size // heads default."""
+    rotary = context.get_rotary(32, 10000.0)
+
+    assert rotary.inv_freq.numel() == 16
+
+
+def test_get_rotary_is_cached(context):
+    first = context.get_rotary(64, 10000.0)
+
+    assert context.get_rotary(64, 10000.0) is first
+
+
+class _StopAfterRotary(Exception):
+    """Ends the fallback at the call under test, before it wants a workspace."""
+
+
+def test_the_fallback_passes_apply_rotary_pos_emb_four_arguments(monkeypatch, context):
+    """Asserts this repo's call, not the library's signature.
+
+    transformers 5.0 dropped the deprecated `position_ids` parameter, so the fifth
+    positional slot became `unsqueeze_dim`:
+
+        4.51.3 .. 4.57.0   (q, k, cos, sin, position_ids=None, unsqueeze_dim=1)
+        5.0.0  .. 5.16.1   (q, k, cos, sin, unsqueeze_dim=1)
+
+    Passing `position_ids` there reaches `unsqueeze(dim=...)` as a tensor. Checking the
+    library's own signature would not catch that, since the mistake is in the caller; the
+    recorded call has to come from `softmax_context_fallback` itself.
+
+    The recorder raises so execution stops at the rotary block. `update_cache` sits two
+    lines below and needs a workspace, which is not what this is about.
+    """
+    llama = pytest.importorskip("transformers.models.llama.modeling_llama")
+
+    recorded = {}
+
+    def recorder(*args, **kwargs):
+        recorded["args"], recorded["kwargs"] = args, kwargs
+        raise _StopAfterRotary
+
+    monkeypatch.setattr(llama, "apply_rotary_pos_emb", recorder)
+
+    heads, head_dim, seq_len, rotary_dim = 4, 16, 8, 16
+    query_key_value = torch.randn(1, seq_len, 3 * heads * head_dim)
+    position_ids = torch.arange(seq_len).unsqueeze(0)
+
+    config = DeepSpeedInferenceConfig(hidden_size=heads * head_dim, heads=heads, dtype=torch.float32)
+    op = SoftmaxContextOp.__new__(SoftmaxContextOp)
+    op.config = config
+
+    with pytest.raises(_StopAfterRotary):
+        op.softmax_context_fallback(query_key_value, None, rotary_dim, True, False, heads, heads, 1.0, False, False, 0,
+                                    False, 0, 1, None, 10000.0, True, 0, position_ids)
+
+    assert len(recorded["args"]) == 4, \
+        f"the fallback passed {len(recorded['args'])} positional arguments; the fifth is unsqueeze_dim"
+    assert not recorded["kwargs"], f"unexpected keyword arguments: {sorted(recorded['kwargs'])}"