diff --git a/test/registered/models_e2e/test_inkling_small_nvfp4.py b/test/registered/models_e2e/test_inkling_small_nvfp4.py
index c32fb6932..98e2b564d 100644
--- a/test/registered/models_e2e/test_inkling_small_nvfp4.py
+++ b/test/registered/models_e2e/test_inkling_small_nvfp4.py
@@ -12,6 +12,7 @@ cards.
 """
 
 import os
+import random
 import unittest
 from types import SimpleNamespace
 from urllib.parse import urlparse
@@ -19,7 +20,18 @@ from urllib.parse import urlparse
 from sglang.srt.utils import kill_process_tree
 from sglang.test.ci.ci_register import register_cuda_ci
 
+# Aliased for the same reason as the single-turn helpers above.
+from sglang.test.kl_multiturn_utils import (
+    make_mamba_decode_assert,
+)
+from sglang.test.kl_multiturn_utils import (
+    test_input_output_logprobs_match_decode_cache_hit_helper as assert_multiturn_decode_cache_hit,
+)
+
 # Aliased so pytest does not collect the imported `test_`-prefixed helpers as tests.
+from sglang.test.kl_test_utils import (
+    get_input_ids,
+)
 from sglang.test.kl_test_utils import (
     test_input_output_logprobs_match_decode_cache_hit_helper as assert_logprobs_match_decode_cache_hit,
 )
@@ -36,7 +48,7 @@ from sglang.test.test_utils import (
     popen_launch_server,
 )
 
-register_cuda_ci(est_time=1200, stage="extra-b", runner_config="4-gpu-b200")
+register_cuda_ci(est_time=1700, stage="extra-b", runner_config="4-gpu-b200")
 
 _MODEL_PATH = os.environ.get(
     "INKLING_SMALL_TEST_MODEL_PATH", "thinkingmachines/Inkling-Small-NVFP4"
@@ -203,5 +215,123 @@ class TestInklingSmallNvfp4Deterministic(CustomTestCase):
         self._run(assert_logprobs_match_decode_cache_hit, min_cache_hit_ratio=0.99)
 
 
+# The multi-turn branching harness, unlike the single-turn helpers above, replays
+# turn N on top of turn N-1's history, so cache hits land at many different
+# prefix lengths and nine interleaved branches share prefixes before diverging.
+# That is what reaches the decode-side track save.
+KL_HICACHE_TRACK_INTERVAL = 128
+
+
+def _random_suffixes(n: int, length: int, seed: int) -> list[list[int]]:
+    rng = random.Random(seed)
+    return [[rng.randint(1, 30000) for _ in range(length)] for _ in range(n)]
+
+
+class TestInklingSmallNvfp4HiCacheDeterministic(CustomTestCase):
+    """HiCache round trip must be bit exact, since nothing about moving a state
+    to host memory and back is allowed to change it.
+
+    Every knob here is load bearing, and dropping any one of them takes the
+    measurement back to zero even when the state layer is wrong:
+
+    - hicache write_through, so an insert copies to host immediately
+    - the decode CUDA graph, since the corrupted slot is only read through the
+      captured decode path
+    - a short ``--mamba-track-interval``, so decode actually crosses a track
+      boundary within a turn
+    - pools tight enough to force eviction while requests are live
+    - multi-turn cache hits, because a wrong slot only surfaces once a later hit
+      restores it
+    """
+
+    @classmethod
+    def setUpClass(cls):
+        cls.model = _MODEL_PATH
+        cls.base_url = DEFAULT_URL_FOR_TEST
+        cls.process = popen_launch_server(
+            cls.model,
+            cls.base_url,
+            timeout=DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH,
+            other_args=[
+                "--tp",
+                "4",
+                "--trust-remote-code",
+                "--quantization",
+                "modelopt_fp4",
+                "--attention-backend",
+                "fa4",
+                "--page-size",
+                "128",
+                "--fp4-gemm-backend",
+                "flashinfer_trtllm",
+                "--moe-runner-backend",
+                "flashinfer_trtllm_routed",
+                "--mamba-radix-cache-strategy",
+                "extra_buffer",
+                "--mamba-track-interval",
+                str(KL_HICACHE_TRACK_INTERVAL),
+                "--swa-full-tokens-ratio",
+                "0.1",
+                "--mamba-full-memory-ratio",
+                "0.1",
+                "--mem-fraction-static",
+                "0.85",
+                "--chunked-prefill-size",
+                "2048",
+                "--enable-hierarchical-cache",
+                "--hicache-ratio",
+                "4",
+                "--hicache-write-policy",
+                "write_through",
+                "--hicache-io-backend",
+                "direct",
+                "--hicache-mem-layout",
+                "page_first_direct",
+                "--max-total-tokens",
+                "65536",
+                "--max-mamba-cache-size",
+                "500",
+                "--max-running-requests",
+                "4",
+                "--enable-deterministic-inference",
+            ],
+            env={**os.environ, "SGLANG_ENABLE_UNIFIED_RADIX_TREE": "1"},
+        )
+        cls.input_ids = get_input_ids(cls.model, num_samples=18, trust_remote_code=True)
+
+    @classmethod
+    def tearDownClass(cls):
+        if getattr(cls, "process", None) is not None:
+            kill_process_tree(cls.process.pid)
+
+    def test_multiturn_decode_cache_hit_over_hicache(self):
+        """Nine interleaved branches, three turns, decode hits served through the
+        host tier. Also asserts every hit lands on a track boundary, which the
+        logprob comparison cannot see on its own."""
+        groups, branches = 3, 3
+        n = groups * branches
+        first_turn = []
+        for g in range(groups):
+            base = self.input_ids[g][:512]
+            for _ in range(branches):
+                first_turn.append(list(base))
+
+        assert_multiturn_decode_cache_hit(
+            self.base_url,
+            self.model,
+            KL_DIV_THRESHOLD,
+            first_turn,
+            turn_suffixes=[
+                _random_suffixes(n, 512, seed=300),
+                _random_suffixes(n, 256, seed=400),
+            ],
+            assert_decode_cached_tokens=make_mamba_decode_assert(
+                track_interval=KL_HICACHE_TRACK_INTERVAL
+            ),
+            branches_per_group=branches,
+            max_new_tokens=KL_MAX_NEW_TOKENS,
+        )
+
+
 if __name__ == "__main__":
     unittest.main()