diff --git a/tests/diffusion/layers/test_fused_qk_rope.py b/tests/diffusion/layers/test_fused_qk_rope.py
new file mode 100644
index 00000000000..c37075ba665
--- /dev/null
+++ b/tests/diffusion/layers/test_fused_qk_rope.py
@@ -0,0 +1,125 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+
+import pytest
+import torch
+from diffusers.models.embeddings import apply_rotary_emb
+from vllm.triton_utils import HAS_TRITON
+
+pytestmark = [pytest.mark.core_model, pytest.mark.diffusion]
+
+
+def test_fused_qk_rope_fake_and_cpu_eligibility():
+    from vllm_omni.diffusion.layers.fused_qk_rope import (
+        _fused_qk_rope_fake,
+        fused_qk_rope,
+        fused_qk_rope_supported,
+    )
+
+    q = torch.randn(2, 3, 4, 8, dtype=torch.bfloat16)
+    k = torch.randn_like(q)
+    cos = torch.randn(3, 8)
+    sin = torch.randn_like(cos)
+
+    fake_q, fake_k = _fused_qk_rope_fake(q, k, cos, sin)
+    assert fake_q.shape == q.shape and fake_q.dtype == q.dtype
+    assert fake_k.shape == k.shape and fake_k.dtype == k.dtype
+    assert not fused_qk_rope_supported(q, k, cos, sin)
+    with pytest.raises(ValueError, match="contiguous CUDA BF16"):
+        fused_qk_rope(q, k, cos, sin)
+
+
+def _cuda_inputs(batch: int, sequence: int, heads: int = 24, head_dim: int = 128):
+    q = torch.randn(batch, sequence, heads, head_dim, device="cuda", dtype=torch.bfloat16)
+    k = torch.randn_like(q)
+    # Deliberately do not repeat adjacent table columns.  Diffusers consumes
+    # full-width tables, so even and odd outputs may use different values.
+    cos = torch.randn(sequence, head_dim, device="cuda", dtype=torch.float32)
+    sin = torch.randn_like(cos)
+    return q, k, cos, sin
+
+
+def _reference(q, k, cos, sin):
+    rotary_emb = (cos, sin)
+    return (
+        apply_rotary_emb(q, rotary_emb, sequence_dim=1),
+        apply_rotary_emb(k, rotary_emb, sequence_dim=1),
+    )
+
+
+@pytest.mark.cuda
+@pytest.mark.skipif(not torch.cuda.is_available(), reason="CUDA required")
+@pytest.mark.skipif(not HAS_TRITON, reason="Triton required")
+@pytest.mark.parametrize("sequence", [512, 4096, 4608])
+def test_fused_qk_rope_is_bit_exact_at_longcat_production_shapes(sequence):
+    from vllm_omni.diffusion.layers.fused_qk_rope import _launch_fused_qk_rope, fused_qk_rope
+
+    torch.manual_seed(sequence)
+    with torch.inference_mode():
+        q, k, cos, sin = _cuda_inputs(1, sequence)
+        expected = _reference(q, k, cos, sin)
+        for actual in (
+            _launch_fused_qk_rope(q, k, cos, sin),
+            fused_qk_rope(q, k, cos, sin),
+        ):
+            assert torch.equal(actual[0], expected[0])
+            assert torch.equal(actual[1], expected[1])
+
+
+@pytest.mark.cuda
+@pytest.mark.skipif(not torch.cuda.is_available(), reason="CUDA required")
+@pytest.mark.skipif(not HAS_TRITON, reason="Triton required")
+def test_fused_qk_rope_is_bit_exact_for_batch_and_full_width_odd_even_tables():
+    from vllm_omni.diffusion.layers.fused_qk_rope import fused_qk_rope
+
+    torch.manual_seed(11)
+    with torch.inference_mode():
+        q, k, cos, sin = _cuda_inputs(2, 17, heads=3)
+        assert not torch.equal(cos[:, ::2], cos[:, 1::2])
+        assert not torch.equal(sin[:, ::2], sin[:, 1::2])
+        expected = _reference(q, k, cos, sin)
+        actual = fused_qk_rope(q, k, cos, sin)
+
+    assert torch.equal(actual[0], expected[0])
+    assert torch.equal(actual[1], expected[1])
+
+
+@pytest.mark.cuda
+@pytest.mark.skipif(not torch.cuda.is_available(), reason="CUDA required")
+@pytest.mark.skipif(not HAS_TRITON, reason="Triton required")
+def test_fused_qk_rope_rejects_noncontiguous_and_non_fp32_tables():
+    from vllm_omni.diffusion.layers.fused_qk_rope import fused_qk_rope_supported
+
+    q, k, cos, sin = _cuda_inputs(1, 8, heads=2)
+    q_noncontiguous = torch.randn(1, 8, 2, 256, device="cuda", dtype=torch.bfloat16)[..., ::2]
+    k_noncontiguous = torch.randn_like(q_noncontiguous)
+    cos_noncontiguous = torch.randn(8, 256, device="cuda")[:, ::2]
+    sin_noncontiguous = torch.randn(8, 256, device="cuda")[:, ::2]
+    with torch.inference_mode():
+        assert fused_qk_rope_supported(q, k, cos, sin)
+        assert not fused_qk_rope_supported(q_noncontiguous, k_noncontiguous, cos, sin)
+        assert not fused_qk_rope_supported(q, k, cos_noncontiguous, sin_noncontiguous)
+        assert not fused_qk_rope_supported(q, k, cos.to(torch.bfloat16), sin.to(torch.bfloat16))
+
+        q_wide = torch.randn(1, 8, 2, 256, device="cuda", dtype=torch.bfloat16)
+        k_wide = torch.randn_like(q_wide)
+        cos_wide = torch.randn(8, 256, device="cuda")
+        sin_wide = torch.randn_like(cos_wide)
+        assert not fused_qk_rope_supported(q_wide, k_wide, cos_wide, sin_wide)
+
+
+@pytest.mark.cuda
+@pytest.mark.skipif(not torch.cuda.is_available(), reason="CUDA required")
+@pytest.mark.skipif(not HAS_TRITON, reason="Triton required")
+def test_fused_qk_rope_custom_op_has_fullgraph_fake():
+    from vllm_omni.diffusion.layers.fused_qk_rope import fused_qk_rope
+
+    torch.manual_seed(29)
+    with torch.inference_mode():
+        q, k, cos, sin = _cuda_inputs(1, 19, heads=3)
+        expected = _reference(q, k, cos, sin)
+        compiled = torch.compile(fused_qk_rope, dynamic=True, fullgraph=True)
+        actual = compiled(q, k, cos, sin)
+
+    assert torch.equal(actual[0], expected[0])
+    assert torch.equal(actual[1], expected[1])
diff --git a/tests/diffusion/models/longcat_image/test_longcat_image_transformer.py b/tests/diffusion/models/longcat_image/test_longcat_image_transformer.py
new file mode 100644
index 00000000000..51cedbb8f00
--- /dev/null
+++ b/tests/diffusion/models/longcat_image/test_longcat_image_transformer.py
@@ -0,0 +1,239 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+
+from contextlib import nullcontext
+from types import SimpleNamespace
+
+import pytest
+import torch
+from diffusers.models.embeddings import apply_rotary_emb
+
+pytestmark = [pytest.mark.core_model, pytest.mark.cpu, pytest.mark.diffusion]
+
+
+@pytest.fixture(autouse=True)
+def _clear_qk_rope_signature_caches():
+    from vllm_omni.diffusion.models.longcat_image import longcat_image_transformer as longcat
+
+    longcat._FAILED_QK_ROPE_SIGNATURES.clear()
+    yield
+    longcat._FAILED_QK_ROPE_SIGNATURES.clear()
+
+
+def _inputs(sequence: int = 5, head_dim: int = 8):
+    q = torch.randn(2, sequence, 3, head_dim, dtype=torch.bfloat16)
+    k = torch.randn_like(q)
+    cos = torch.randn(sequence, head_dim)
+    sin = torch.randn_like(cos)
+    return q, k, (cos, sin)
+
+
+def _reference(q, k, rotary_emb):
+    return (
+        apply_rotary_emb(q, rotary_emb, sequence_dim=1),
+        apply_rotary_emb(k, rotary_emb, sequence_dim=1),
+    )
+
+
+def test_prepare_rotary_emb_resolves_threshold_once_only_when_enabled(monkeypatch):
+    from vllm_omni.diffusion.models.longcat_image import longcat_image_transformer as longcat
+
+    calls = 0
+
+    def resolve(default):
+        nonlocal calls
+        calls += 1
+        assert default == 512
+        return 37
+
+    monkeypatch.setattr(longcat, "fused_qk_norm_rope_min_tokens", resolve)
+    txt_cos, txt_sin = torch.randn(2, 8), torch.randn(2, 8)
+    img_cos, img_sin = torch.randn(3, 8), torch.randn(3, 8)
+    native = longcat._prepare_rotary_emb(txt_cos, txt_sin, img_cos, img_sin, enable_fusion=False)
+    fused = longcat._prepare_rotary_emb(txt_cos, txt_sin, img_cos, img_sin, enable_fusion=True)
+
+    assert calls == 1
+    assert len(native) == 2
+    assert len(fused) == 3 and fused[2] == 37
+    assert torch.equal(native[0], fused[0])
+    assert torch.equal(native[1], fused[1])
+
+
+@pytest.mark.parametrize(
+    ("mode", "sp_size"),
+    [
+        ("unsupported", 1),
+        ("compile", 1),
+        ("grad", 1),
+        ("capture", 1),
+        ("sequence_parallel", 2),
+        ("below_threshold", 1),
+    ],
+)
+def test_qk_rope_non_eager_modes_use_exact_original_path(monkeypatch, mode, sp_size):
+    from vllm_omni.diffusion.models.longcat_image import longcat_image_transformer as longcat
+
+    torch.manual_seed(1)
+    q, k, rotary_emb = _inputs()
+    expected = _reference(q, k, rotary_emb)
+    monkeypatch.setattr(torch.compiler, "is_compiling", lambda: mode == "compile")
+    monkeypatch.setattr(torch.cuda, "is_current_stream_capturing", lambda: mode == "capture")
+    monkeypatch.setattr(longcat, "fused_qk_rope_supported", lambda *args: mode != "unsupported")
+    monkeypatch.setattr(
+        longcat,
+        "fused_qk_rope",
+        lambda *args: (_ for _ in ()).throw(AssertionError("fallback called fused op")),
+    )
+
+    context = nullcontext() if mode == "grad" else torch.no_grad()
+    min_tokens = q.shape[0] * q.shape[1] + 1 if mode == "below_threshold" else 0
+    with context:
+        actual = longcat._apply_qk_rope(q, k, rotary_emb, sp_size, min_tokens)
+
+    assert torch.equal(actual[0], expected[0])
+    assert torch.equal(actual[1], expected[1])
+
+
+def test_qk_rope_eligible_path_skips_runtime_parity_check(monkeypatch):
+    from vllm_omni.diffusion.models.longcat_image import longcat_image_transformer as longcat
+
+    torch.manual_seed(2)
+    monkeypatch.setattr(torch.compiler, "is_compiling", lambda: False)
+    monkeypatch.setattr(torch.cuda, "is_current_stream_capturing", lambda: False)
+    monkeypatch.setattr(longcat, "fused_qk_rope_supported", lambda *args: True)
+    fused_calls = 0
+
+    def fused(query, key, cos, sin):
+        nonlocal fused_calls
+        fused_calls += 1
+        return query + 1, key + 2
+
+    monkeypatch.setattr(
+        longcat,
+        "_apply_qk_rope_reference",
+        lambda *args: (_ for _ in ()).throw(AssertionError("eligible path ran the native parity check")),
+    )
+    monkeypatch.setattr(longcat, "fused_qk_rope", fused)
+
+    with torch.no_grad():
+        q, k, rotary_emb = _inputs()
+        actual = longcat._apply_qk_rope(q, k, rotary_emb, 1, 0)
+
+    assert fused_calls == 1
+    assert torch.equal(actual[0], q + 1)
+    assert torch.equal(actual[1], k + 2)
+
+
+def test_qk_rope_launch_failure_permanently_falls_back(monkeypatch):
+    from vllm_omni.diffusion.models.longcat_image import longcat_image_transformer as longcat
+
+    torch.manual_seed(3)
+    monkeypatch.setattr(torch.compiler, "is_compiling", lambda: False)
+    monkeypatch.setattr(torch.cuda, "is_current_stream_capturing", lambda: False)
+    monkeypatch.setattr(longcat, "fused_qk_rope_supported", lambda *args: True)
+    fused_calls = 0
+
+    def broken_fused(query, key, cos, sin):
+        nonlocal fused_calls
+        fused_calls += 1
+        raise RuntimeError("kernel failed")
+
+    monkeypatch.setattr(longcat, "fused_qk_rope", broken_fused)
+    q, k, rotary_emb = _inputs()
+    expected = _reference(q, k, rotary_emb)
+    with torch.no_grad():
+        first = longcat._apply_qk_rope(q, k, rotary_emb, 1, 0)
+        second = longcat._apply_qk_rope(q, k, rotary_emb, 1, 0)
+
+    assert fused_calls == 1
+    assert len(longcat._FAILED_QK_ROPE_SIGNATURES) == 1
+    for actual in (first, second):
+        assert torch.equal(actual[0], expected[0])
+        assert torch.equal(actual[1], expected[1])
+
+
+def test_failed_qk_rope_signature_cache_is_bounded():
+    from vllm_omni.diffusion.models.longcat_image import longcat_image_transformer as longcat
+
+    for index in range(longcat._FAILED_QK_ROPE_SIGNATURES_MAX_SIZE + 1):
+        longcat._record_failed_qk_rope_signature((index,))
+
+    assert len(longcat._FAILED_QK_ROPE_SIGNATURES) == longcat._FAILED_QK_ROPE_SIGNATURES_MAX_SIZE
+    assert (0,) not in longcat._FAILED_QK_ROPE_SIGNATURES
+    assert (longcat._FAILED_QK_ROPE_SIGNATURES_MAX_SIZE,) in longcat._FAILED_QK_ROPE_SIGNATURES
+
+
+class _FakeQKV(torch.nn.Module):
+    def __init__(self, heads: int, head_dim: int) -> None:
+        super().__init__()
+        self.num_heads = heads
+        self.num_kv_heads = heads
+        self.width = heads * head_dim
+
+    def forward(self, x):
+        return torch.cat((x, x + 1, x + 2), dim=-1), None
+
+
+class _AddNorm(torch.nn.Module):
+    def __init__(self, value: float) -> None:
+        super().__init__()
+        self.value = value
+
+    def forward(self, x):
+        return x + self.value
+
+
+class _CaptureAttention(torch.nn.Module):
+    def forward(self, query, key, value, metadata=None):
+        del key, value, metadata
+        return query
+
+
+class _PassthroughLinear(torch.nn.Module):
+    def forward(self, x):
+        return x, None
+
+
+def test_dual_attention_keeps_native_norm_and_text_image_concat_order(monkeypatch):
+    from vllm_omni.diffusion.models.longcat_image import longcat_image_transformer as longcat
+
+    attention = longcat.LongCatImageAttention.__new__(longcat.LongCatImageAttention)
+    torch.nn.Module.__init__(attention)
+    attention.parallel_config = SimpleNamespace(sequence_parallel_size=1)
+    attention.head_dim = 4
+    attention.added_kv_proj_dim = 8
+    attention.to_qkv = _FakeQKV(2, 4)
+    attention.add_kv_proj = _FakeQKV(2, 4)
+    attention.norm_q = _AddNorm(10)
+    attention.norm_k = _AddNorm(20)
+    attention.norm_added_q = _AddNorm(100)
+    attention.norm_added_k = _AddNorm(200)
+    attention.attn = _CaptureAttention()
+    attention.to_out = _PassthroughLinear()
+    attention.to_add_out = _PassthroughLinear()
+
+    captured = []
+
+    def paired(query, key, rotary_emb, sp_size, min_tokens):
+        captured.append((query.clone(), key.clone(), rotary_emb, sp_size, min_tokens))
+        return query, key
+
+    monkeypatch.setattr(longcat, "_apply_qk_rope", paired)
+    image = torch.randn(1, 3, 8)
+    text = torch.randn(1, 2, 8)
+    rotary_pair = (torch.randn(5, 4), torch.randn(5, 4))
+    rotary_emb = (*rotary_pair, 0)
+    image_out, text_out = attention(image, text, rotary_emb)
+
+    image_q = image.unflatten(-1, (2, 4))
+    text_q = text.unflatten(-1, (2, 4))
+    expected_q = torch.cat((text_q + 100, image_q + 10), dim=1)
+    expected_k = torch.cat((text_q + 1 + 200, image_q + 1 + 20), dim=1)
+    assert len(captured) == 1
+    assert torch.equal(captured[0][0], expected_q)
+    assert torch.equal(captured[0][1], expected_k)
+    assert captured[0][2][0] is rotary_pair[0]
+    assert captured[0][2][1] is rotary_pair[1]
+    assert captured[0][3:] == (1, 0)
+    assert image_out.shape == image.shape
+    assert text_out.shape == text.shape
diff --git a/vllm_omni/diffusion/layers/fused_qk_rope.py b/vllm_omni/diffusion/layers/fused_qk_rope.py
new file mode 100644
index 00000000000..95b24451b12
--- /dev/null
+++ b/vllm_omni/diffusion/layers/fused_qk_rope.py
@@ -0,0 +1,251 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+
+"""Bit-exact paired Q/K full-width interleaved RoPE for CUDA.
+
+The operator accepts already-normalized BF16 query and key tensors in BSND
+layout and full-width FP32 cosine/sine tables.  It deliberately performs two
+round-to-nearest FP32 multiplies followed by one round-to-nearest FP32 add,
+then rounds only once when storing BF16 output.  This matches Diffusers'
+``apply_rotary_emb`` arithmetic while combining its separate Q and K calls.
+"""
+
+from __future__ import annotations
+
+import torch
+from torch.library import Library
+from vllm.platforms import current_platform
+from vllm.triton_utils import HAS_TRITON, tl, triton
+from vllm.utils.torch_utils import direct_register_custom_op
+
+_HEAD_DIM = 128
+_HEADS_PER_PROGRAM = 4
+
+
+if HAS_TRITON:
+
+    @triton.jit
+    def _mul_rn_f32(x, y):
+        return tl.inline_asm_elementwise(
+            asm="mul.rn.f32 $0, $1, $2;",
+            constraints="=f,f,f",
+            args=[x, y],
+            dtype=tl.float32,
+            is_pure=True,
+            pack=1,
+        )
+
+    @triton.jit
+    def _add_rn_f32(x, y):
+        return tl.inline_asm_elementwise(
+            asm="add.rn.f32 $0, $1, $2;",
+            constraints="=f,f,f",
+            args=[x, y],
+            dtype=tl.float32,
+            is_pure=True,
+            pack=1,
+        )
+
+    @triton.jit
+    def _qk_rope_exact_kernel(
+        q_ptr,
+        k_ptr,
+        cos_ptr,
+        sin_ptr,
+        q_output_ptr,
+        k_output_ptr,
+        q_stride_token,
+        q_stride_head,
+        q_stride_dim,
+        k_stride_token,
+        k_stride_head,
+        k_stride_dim,
+        q_output_stride_token,
+        q_output_stride_head,
+        q_output_stride_dim,
+        k_output_stride_token,
+        k_output_stride_head,
+        k_output_stride_dim,
+        table_stride_sequence,
+        table_stride_dim,
+        sequence,
+        num_heads: tl.constexpr,
+        head_dim: tl.constexpr,
+        heads_per_program: tl.constexpr,
+    ):
+        token = tl.program_id(0)
+        group = tl.program_id(1)
+        is_key = tl.program_id(2) == 1
+        heads = group * heads_per_program + tl.arange(0, heads_per_program)
+        dims = tl.arange(0, head_dim)
+        valid = heads[:, None] < num_heads
+
+        q_offsets = token * q_stride_token + heads[:, None] * q_stride_head + dims[None, :] * q_stride_dim
+        k_offsets = token * k_stride_token + heads[:, None] * k_stride_head + dims[None, :] * k_stride_dim
+        input_ptrs = tl.where(is_key, k_ptr + k_offsets, q_ptr + q_offsets)
+
+        pair_dims = dims ^ 1
+        q_pair_offsets = token * q_stride_token + heads[:, None] * q_stride_head + pair_dims[None, :] * q_stride_dim
+        k_pair_offsets = token * k_stride_token + heads[:, None] * k_stride_head + pair_dims[None, :] * k_stride_dim
+        pair_ptrs = tl.where(is_key, k_ptr + k_pair_offsets, q_ptr + q_pair_offsets)
+        values = tl.load(input_ptrs, mask=valid, other=0.0).to(tl.float32)
+        pairs = tl.load(pair_ptrs, mask=valid, other=0.0).to(tl.float32)
+        signed_pairs = tl.where((dims[None, :] & 1) == 0, -pairs, pairs)
+
+        sequence_index = token % sequence
+        table_offsets = sequence_index * table_stride_sequence + dims * table_stride_dim
+        cos = tl.load(cos_ptr + table_offsets).to(tl.float32)[None, :]
+        sin = tl.load(sin_ptr + table_offsets).to(tl.float32)[None, :]
+
+        # Do not let the compiler contract this expression into an FMA.  The
+        # reference has two independently rounded FP32 multiplies and one
+        # independently rounded FP32 add, followed by the final BF16 store.
+        first = _mul_rn_f32(values, cos)
+        second = _mul_rn_f32(signed_pairs, sin)
+        output = _add_rn_f32(first, second)
+        q_output_offsets = (
+            token * q_output_stride_token + heads[:, None] * q_output_stride_head + dims[None, :] * q_output_stride_dim
+        )
+        k_output_offsets = (
+            token * k_output_stride_token + heads[:, None] * k_output_stride_head + dims[None, :] * k_output_stride_dim
+        )
+        output_ptrs = tl.where(
+            is_key,
+            k_output_ptr + k_output_offsets,
+            q_output_ptr + q_output_offsets,
+        )
+        tl.store(output_ptrs, output, mask=valid)
+
+
+def fused_qk_rope_supported(
+    q: torch.Tensor,
+    k: torch.Tensor,
+    cos: torch.Tensor,
+    sin: torch.Tensor,
+) -> bool:
+    """Return whether the exact CUDA kernel can consume these tensors."""
+
+    if not (
+        HAS_TRITON
+        and torch.version.hip is None
+        and current_platform.is_cuda()
+        and not torch.is_grad_enabled()
+        and q.is_cuda
+        and k.is_cuda
+        and q.device == k.device
+        and q.dtype is torch.bfloat16
+        and k.dtype is q.dtype
+        and q.ndim == 4
+        and k.shape == q.shape
+        and q.numel() > 0
+        and q.is_contiguous()
+        and k.is_contiguous()
+    ):
+        return False
+
+    batch, sequence, _heads, head_dim = q.shape
+    del batch
+    if head_dim != _HEAD_DIM:
+        return False
+    if not (
+        cos.shape == (sequence, head_dim)
+        and sin.shape == cos.shape
+        and cos.device == q.device
+        and sin.device == q.device
+        and cos.dtype is torch.float32
+        and sin.dtype is torch.float32
+        and cos.is_contiguous()
+        and sin.is_contiguous()
+    ):
+        return False
+    return True
+
+
+def _launch_fused_qk_rope(
+    q: torch.Tensor,
+    k: torch.Tensor,
+    cos: torch.Tensor,
+    sin: torch.Tensor,
+) -> tuple[torch.Tensor, torch.Tensor]:
+    q_output = torch.empty_like(q)
+    k_output = torch.empty_like(k)
+    tokens = q.shape[0] * q.shape[1]
+    head_groups = triton.cdiv(q.shape[2], _HEADS_PER_PROGRAM)
+    grid = (tokens, head_groups, 2)
+    with torch.accelerator.device_index(q.device.index):
+        _qk_rope_exact_kernel[grid](
+            q,
+            k,
+            cos,
+            sin,
+            q_output,
+            k_output,
+            q.stride(1),
+            q.stride(2),
+            q.stride(3),
+            k.stride(1),
+            k.stride(2),
+            k.stride(3),
+            q_output.stride(1),
+            q_output.stride(2),
+            q_output.stride(3),
+            k_output.stride(1),
+            k_output.stride(2),
+            k_output.stride(3),
+            cos.stride(0),
+            cos.stride(1),
+            q.shape[1],
+            num_heads=q.shape[2],
+            head_dim=q.shape[-1],
+            heads_per_program=_HEADS_PER_PROGRAM,
+            num_warps=4,
+        )
+    return q_output, k_output
+
+
+def _fused_qk_rope_impl(
+    q: torch.Tensor,
+    k: torch.Tensor,
+    cos: torch.Tensor,
+    sin: torch.Tensor,
+) -> tuple[torch.Tensor, torch.Tensor]:
+    if not fused_qk_rope_supported(q, k, cos, sin):
+        raise ValueError("fused_qk_rope received unsupported inputs")
+    return _launch_fused_qk_rope(q, k, cos, sin)
+
+
+def _fused_qk_rope_fake(
+    q: torch.Tensor,
+    k: torch.Tensor,
+    cos: torch.Tensor,
+    sin: torch.Tensor,
+) -> tuple[torch.Tensor, torch.Tensor]:
+    del cos, sin
+    return torch.empty_like(q), torch.empty_like(k)
+
+
+_OMNI_OP_LIB = Library("vllm_omni", "FRAGMENT")
+if not hasattr(torch.ops.vllm_omni, "fused_qk_rope"):
+    direct_register_custom_op(
+        op_name="fused_qk_rope",
+        op_func=_fused_qk_rope_impl,
+        fake_impl=_fused_qk_rope_fake,
+        mutates_args=[],
+        target_lib=_OMNI_OP_LIB,
+    )
+
+
+def fused_qk_rope(
+    q: torch.Tensor,
+    k: torch.Tensor,
+    cos: torch.Tensor,
+    sin: torch.Tensor,
+) -> tuple[torch.Tensor, torch.Tensor]:
+    """Apply paired full-width adjacent/interleaved RoPE on CUDA."""
+
+    if not fused_qk_rope_supported(q, k, cos, sin):
+        raise ValueError("fused_qk_rope requires contiguous CUDA BF16 Q/K and contiguous full-width CUDA FP32 tables")
+    return torch.ops.vllm_omni.fused_qk_rope(q, k, cos, sin)
+
+
+__all__ = ["fused_qk_rope", "fused_qk_rope_supported"]
diff --git a/vllm_omni/diffusion/models/longcat_image/longcat_image_transformer.py b/vllm_omni/diffusion/models/longcat_image/longcat_image_transformer.py
index 3cde2a868a3..a93d147047a 100644
--- a/vllm_omni/diffusion/models/longcat_image/longcat_image_transformer.py
+++ b/vllm_omni/diffusion/models/longcat_image/longcat_image_transformer.py
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: Apache-2.0
-# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
 
+from collections import OrderedDict
 from collections.abc import Iterable
 from typing import Any
 
@@ -16,6 +17,8 @@
 from vllm.model_executor.layers.layernorm import RMSNorm
 from vllm.model_executor.layers.linear import ColumnParallelLinear, QKVParallelLinear, RowParallelLinear
 from vllm.model_executor.model_loader.weight_utils import default_weight_loader
+from vllm.platforms import current_platform
+from vllm.triton_utils import HAS_TRITON
 
 from vllm_omni.diffusion.attention.backends.abstract import AttentionMetadata
 from vllm_omni.diffusion.attention.layer import Attention
@@ -26,10 +29,150 @@
     SequenceParallelOutput,
 )
 from vllm_omni.diffusion.forward_context import get_forward_context
+from vllm_omni.diffusion.layers.fused_qk_norm_rope import fused_qk_norm_rope_min_tokens
+from vllm_omni.diffusion.layers.fused_qk_rope import fused_qk_rope, fused_qk_rope_supported
 from vllm_omni.platforms import current_omni_platform
 
 logger = init_logger(__name__)
 
+RotaryEmbedding = tuple[torch.Tensor, torch.Tensor] | tuple[torch.Tensor, torch.Tensor, int]
+
+# All LongCat production attention spans contain at least 512 tokens.  Reuse
+# the shared Q/K fusion threshold override so deployments can retain a
+# hardware-specific crossover without adding another environment variable.
+_FUSED_MIN_TOKENS = 512
+_FUSED_QK_ROPE = HAS_TRITON and current_platform.is_cuda()
+_FAILED_QK_ROPE_SIGNATURES_MAX_SIZE = 128
+_FAILED_QK_ROPE_SIGNATURES: OrderedDict[tuple[object, ...], None] = OrderedDict()
+
+
+def _fusion_enabled(sequence_parallel_size: int | None, *, enforce_eager: bool) -> bool:
+    return (
+        _FUSED_QK_ROPE
+        and enforce_eager
+        and not torch.compiler.is_compiling()
+        and not torch.is_grad_enabled()
+        and not (sequence_parallel_size is not None and sequence_parallel_size > 1)
+    )
+
+
+def _prepare_rotary_emb(
+    txt_cos: torch.Tensor,
+    txt_sin: torch.Tensor,
+    img_cos: torch.Tensor,
+    img_sin: torch.Tensor,
+    *,
+    enable_fusion: bool,
+) -> RotaryEmbedding:
+    """Join text/image tables and resolve the shared token gate once."""
+
+    joint = torch.cat((txt_cos, img_cos), dim=0), torch.cat((txt_sin, img_sin), dim=0)
+    if not enable_fusion:
+        return joint
+    return joint[0], joint[1], fused_qk_norm_rope_min_tokens(_FUSED_MIN_TOKENS)
+
+
+def _apply_qk_rope_reference(
+    query: torch.Tensor,
+    key: torch.Tensor,
+    rotary_emb: tuple[torch.Tensor, torch.Tensor],
+) -> tuple[torch.Tensor, torch.Tensor]:
+    return (
+        apply_rotary_emb(query, rotary_emb, sequence_dim=1),
+        apply_rotary_emb(key, rotary_emb, sequence_dim=1),
+    )
+
+
+def _qk_rope_signature(
+    query: torch.Tensor,
+    key: torch.Tensor,
+    cos: torch.Tensor,
+    sin: torch.Tensor,
+) -> tuple[object, ...]:
+    """Identify a runtime layout for failure-cache fallback."""
+
+    return (
+        query.device.type,
+        query.device.index,
+        query.dtype,
+        tuple(query.shape),
+        tuple(query.stride()),
+        tuple(key.shape),
+        tuple(key.stride()),
+        cos.dtype,
+        tuple(cos.shape),
+        tuple(cos.stride()),
+        tuple(sin.stride()),
+    )
+
+
+def _is_failed_qk_rope_signature(signature: tuple[object, ...]) -> bool:
+    if signature not in _FAILED_QK_ROPE_SIGNATURES:
+        return False
+    _FAILED_QK_ROPE_SIGNATURES.move_to_end(signature)
+    return True
+
+
+def _record_failed_qk_rope_signature(signature: tuple[object, ...]) -> None:
+    _FAILED_QK_ROPE_SIGNATURES[signature] = None
+    _FAILED_QK_ROPE_SIGNATURES.move_to_end(signature)
+    while len(_FAILED_QK_ROPE_SIGNATURES) > _FAILED_QK_ROPE_SIGNATURES_MAX_SIZE:
+        _FAILED_QK_ROPE_SIGNATURES.popitem(last=False)
+
+
+def _can_use_fused_qk_rope(
+    query: torch.Tensor,
+    key: torch.Tensor,
+    cos: torch.Tensor,
+    sin: torch.Tensor,
+    sequence_parallel_size: int | None,
+    min_tokens: int | None,
+) -> bool:
+    """Keep compile, autograd, capture, SP, and unsupported inputs native."""
+
+    if (
+        torch.compiler.is_compiling()
+        or torch.is_grad_enabled()
+        or (sequence_parallel_size is not None and sequence_parallel_size > 1)
+        or min_tokens is None
+        or not fused_qk_rope_supported(query, key, cos, sin)
+        or torch.cuda.is_current_stream_capturing()
+    ):
+        return False
+    return query.shape[0] * query.shape[1] >= min_tokens
+
+
+def _apply_qk_rope(
+    query: torch.Tensor,
+    key: torch.Tensor,
+    rotary_emb: RotaryEmbedding | None,
+    sequence_parallel_size: int | None,
+    min_tokens: int | None,
+) -> tuple[torch.Tensor, torch.Tensor]:
+    """Apply one paired RoPE launch, falling back after launch failures."""
+
+    if rotary_emb is None:
+        return query, key
+    rotary_pair = rotary_emb[:2]
+    cos, sin = rotary_pair
+    if not _can_use_fused_qk_rope(query, key, cos, sin, sequence_parallel_size, min_tokens):
+        return _apply_qk_rope_reference(query, key, rotary_pair)
+
+    signature = _qk_rope_signature(query, key, cos, sin)
+    if _is_failed_qk_rope_signature(signature):
+        return _apply_qk_rope_reference(query, key, rotary_pair)
+
+    try:
+        return fused_qk_rope(query, key, cos, sin)
+    except Exception as exc:  # noqa: BLE001 - optimized-path failures must fall back
+        _record_failed_qk_rope_signature(signature)
+        logger.warning(
+            "Disabling LongCat paired Q/K RoPE fusion for signature %s after failure: %s",
+            signature,
+            exc,
+        )
+        return _apply_qk_rope_reference(query, key, rotary_pair)
+
 
 class FeedForward(nn.Module):
     def __init__(self, dim: int, dim_out: int | None = None, mult: int = 4, bias: bool = True):
@@ -121,7 +264,7 @@ def _sp_attention_with_rope(
         text_key: torch.Tensor,
         text_value: torch.Tensor,
         text_seq_len: int,
-        image_rotary_emb: tuple[torch.Tensor, torch.Tensor] | None,
+        image_rotary_emb: RotaryEmbedding | None,
     ) -> torch.Tensor:
         """
         Apply RoPE separately to text and image Q/K, then run SP attention with joint tensors.
@@ -139,7 +282,7 @@ def _sp_attention_with_rope(
             Attention output with shape (B, txt_len + img_len/SP, H, D)
         """
         if image_rotary_emb is not None:
-            freqs_cos, freqs_sin = image_rotary_emb
+            freqs_cos, freqs_sin = image_rotary_emb[:2]
             txt_rotary_emb = (freqs_cos[:text_seq_len], freqs_sin[:text_seq_len])
             img_rotary_emb_split = (freqs_cos[text_seq_len:], freqs_sin[text_seq_len:])
             # Apply RoPE to image Q/K
@@ -165,7 +308,7 @@ def forward(
         self,
         hidden_states: torch.Tensor,
         encoder_hidden_states: torch.Tensor | None = None,
-        image_rotary_emb: torch.Tensor | None = None,
+        image_rotary_emb: RotaryEmbedding | None = None,
         **kwargs,
     ) -> torch.Tensor:
         """
@@ -196,6 +339,8 @@ def forward(
 
         query = self.norm_q(query)
         key = self.norm_k(key)
+        rotary_pair = image_rotary_emb[:2] if image_rotary_emb is not None else None
+        min_tokens = image_rotary_emb[2] if image_rotary_emb is not None and len(image_rotary_emb) > 2 else None
 
         if self.added_kv_proj_dim is not None:
             encoder_qkv, _ = self.add_kv_proj(encoder_hidden_states)
@@ -222,7 +367,7 @@ def forward(
                     text_key=encoder_key,
                     text_value=encoder_value,
                     text_seq_len=encoder_query.shape[1],
-                    image_rotary_emb=image_rotary_emb,
+                    image_rotary_emb=rotary_pair,
                 )
             else:
                 # Non-SP Mode: Concat first, then apply RoPE to full sequence
@@ -230,10 +375,15 @@ def forward(
                 joint_key = torch.cat([encoder_key, key], dim=1)
                 joint_value = torch.cat([encoder_value, value], dim=1)
 
-                if image_rotary_emb is not None:
-                    # Apply RoPE to full (text + image) sequence
-                    joint_query = apply_rotary_emb(joint_query, image_rotary_emb, sequence_dim=1)
-                    joint_key = apply_rotary_emb(joint_key, image_rotary_emb, sequence_dim=1)
+                # Keep the native RMSNorm and text-then-image concatenation
+                # order, then combine only the two independent RoPE calls.
+                joint_query, joint_key = _apply_qk_rope(
+                    joint_query,
+                    joint_key,
+                    rotary_pair,
+                    sp_size,
+                    min_tokens,
+                )
 
                 hidden_states = self.attn(
                     joint_query,
@@ -272,13 +422,17 @@ def forward(
                     text_key=key[:, :text_seq_len],
                     text_value=value[:, :text_seq_len],
                     text_seq_len=text_seq_len,
-                    image_rotary_emb=image_rotary_emb,
+                    image_rotary_emb=rotary_pair,
                 )
             else:
                 # Non-SP Mode: standard path
-                if image_rotary_emb is not None:
-                    query = apply_rotary_emb(query, image_rotary_emb, sequence_dim=1)
-                    key = apply_rotary_emb(key, image_rotary_emb, sequence_dim=1)
+                query, key = _apply_qk_rope(
+                    query,
+                    key,
+                    rotary_pair,
+                    sp_size,
+                    min_tokens,
+                )
 
                 hidden_states = self.attn(
                     query,
@@ -345,7 +499,7 @@ def forward(
         hidden_states: torch.Tensor,
         encoder_hidden_states: torch.Tensor,
         temb: torch.Tensor,
-        image_rotary_emb: tuple[torch.Tensor, torch.Tensor] | None = None,
+        image_rotary_emb: RotaryEmbedding | None = None,
         joint_attention_kwargs: dict[str, Any] | None = None,
     ) -> tuple[torch.Tensor, torch.Tensor]:
         norm_hidden_states, gate_msa, shift_mlp, scale_mlp, gate_mlp = self.norm1(hidden_states, emb=temb)
@@ -536,7 +690,7 @@ def forward(
         hidden_states: torch.Tensor,
         encoder_hidden_states: torch.Tensor,
         temb: torch.Tensor,
-        image_rotary_emb: tuple[torch.Tensor, torch.Tensor] | None = None,
+        image_rotary_emb: RotaryEmbedding | None = None,
         joint_attention_kwargs: dict[str, Any] | None = None,
     ) -> tuple[torch.Tensor, torch.Tensor]:
         """
@@ -632,6 +786,7 @@ def __init__(
 
         # Store parallel config for SP support
         self.parallel_config = od_config.parallel_config
+        self.enforce_eager = bool(getattr(od_config, "enforce_eager", False))
 
         self.pos_embed = LongCatImagePosEmbed(theta=10000, axes_dim=axes_dims_rope)
         self.rope_preparer = RoPEPreparer(self.pos_embed)
@@ -701,11 +856,15 @@ def forward(
         # txt_cos/txt_sin (outputs 0, 1) remain replicated for dual-stream attention
         txt_cos, txt_sin, img_cos, img_sin = self.rope_preparer(txt_ids, img_ids)
 
-        # Reconstruct image_rotary_emb with chunked values
-        # Final shape: (txt_seq_len + img_seq_len // SP, head_dim)
-        image_rotary_emb = (
-            torch.cat([txt_cos, img_cos], dim=0),
-            torch.cat([txt_sin, img_sin], dim=0),
+        # Preserve the ordinary full-width tables.  A third scalar only marks
+        # the eligible eager SP=1 route and resolves the shared threshold once
+        # for all attention blocks in this transformer call.
+        image_rotary_emb = _prepare_rotary_emb(
+            txt_cos,
+            txt_sin,
+            img_cos,
+            img_sin,
+            enable_fusion=_fusion_enabled(sp_size, enforce_eager=self.enforce_eager),
         )
 
         for block in self.transformer_blocks: