diff --git a/litellm/caching/dual_cache.py b/litellm/caching/dual_cache.py
index bef04a5c23c..8542d3364df 100644
--- a/litellm/caching/dual_cache.py
+++ b/litellm/caching/dual_cache.py
@@ -150,13 +150,23 @@ class DualCache(BaseCache):
     def set_cache(self, key, value, local_only: bool = False, **kwargs):
         # Update both Redis and in-memory cache
         try:
+            # ``kwargs`` is this call's own dict, so injecting a ttl into it is safe. What must not
+            # happen is one tier's injected ttl reaching the other, so note whether the caller
+            # supplied one before either tier writes back.
+            ttl_given: Final = "ttl" in kwargs
             if self.in_memory_cache is not None:
-                if "ttl" not in kwargs and self.default_in_memory_ttl is not None:
+                if not ttl_given and self.default_in_memory_ttl is not None:
                     kwargs["ttl"] = self.default_in_memory_ttl
 
                 self.in_memory_cache.set_cache(key, value, **kwargs)
 
             if self.redis_cache is not None and local_only is False:
+                if not ttl_given:
+                    redis_ttl = self.default_redis_ttl
+                    if redis_ttl is None:
+                        redis_ttl = self.default_in_memory_ttl
+                    if redis_ttl is not None:
+                        kwargs["ttl"] = redis_ttl
                 self.redis_cache.set_cache(key, value, **kwargs)
         except Exception as e:
             print_verbose(e)
@@ -505,12 +515,19 @@ class DualCache(BaseCache):
     async def async_set_cache(self, key, value, local_only: bool = False, **kwargs):
         print_verbose(f"async set cache: cache key: {key}; local_only: {local_only}; value: {value}")
         try:
+            ttl_given: Final = "ttl" in kwargs
             if self.in_memory_cache is not None:
-                if "ttl" not in kwargs and self.default_in_memory_ttl is not None:
+                if not ttl_given and self.default_in_memory_ttl is not None:
                     kwargs["ttl"] = self.default_in_memory_ttl
                 await self.in_memory_cache.async_set_cache(key, value, **kwargs)
 
             if self.redis_cache is not None and local_only is False:
+                if not ttl_given:
+                    redis_ttl = self.default_redis_ttl
+                    if redis_ttl is None:
+                        redis_ttl = self.default_in_memory_ttl
+                    if redis_ttl is not None:
+                        kwargs["ttl"] = redis_ttl
                 await self.redis_cache.async_set_cache(key, value, **kwargs)
         except Exception as e:
             log_redis_failure(
@@ -537,7 +554,10 @@ class DualCache(BaseCache):
         effective_ttl: Final = self.default_in_memory_ttl if ttl is None else ttl
         if self.in_memory_cache is not None:
             await self.in_memory_cache.async_set_cache(key, value, ttl=effective_ttl)
-        return batch.set(key, value, effective_ttl)
+        redis_ttl = self.default_redis_ttl if ttl is None else ttl
+        if redis_ttl is None:
+            redis_ttl = effective_ttl
+        return batch.set(key, value, redis_ttl)
 
     # async_batch_set_cache
     async def async_set_cache_pipeline(
@@ -548,12 +568,19 @@ class DualCache(BaseCache):
         """
         print_verbose(f"async batch set cache: cache keys: {cache_list}; local_only: {local_only}")
         try:
+            ttl_given: Final = "ttl" in kwargs
             if self.in_memory_cache is not None:
-                if "ttl" not in kwargs and self.default_in_memory_ttl is not None:
+                if not ttl_given and self.default_in_memory_ttl is not None:
                     kwargs["ttl"] = self.default_in_memory_ttl
                 await self.in_memory_cache.async_set_cache_pipeline(cache_list=cache_list, **kwargs)
 
             if self.redis_cache is not None and local_only is False:
+                if not ttl_given:
+                    redis_ttl = self.default_redis_ttl
+                    if redis_ttl is None:
+                        redis_ttl = self.default_in_memory_ttl
+                    if redis_ttl is not None:
+                        kwargs["ttl"] = redis_ttl
                 await self.redis_cache.async_set_cache_pipeline(
                     cache_list=cache_list, ttl=kwargs.pop("ttl", None), **kwargs
                 )
diff --git a/litellm/proxy/common_utils/user_api_key_cache.py b/litellm/proxy/common_utils/user_api_key_cache.py
index 8c830816207..c59412d65f6 100644
--- a/litellm/proxy/common_utils/user_api_key_cache.py
+++ b/litellm/proxy/common_utils/user_api_key_cache.py
@@ -71,17 +71,21 @@ class UserApiKeyCache(DualCache):
         default_redis_ttl: float | None = None,
         key_object_in_memory_cache: InMemoryCache | None = None,
     ) -> None:
+        # The auth cache contract is that Redis mirrors the in-memory TTL when no
+        # explicit Redis TTL is configured (see #43187). Compute the effective
+        # Redis TTL here so DualCache stays generic and does not special-case us.
+        effective_redis_ttl: Final = default_redis_ttl if default_redis_ttl is not None else default_in_memory_ttl
         super().__init__(
             in_memory_cache=in_memory_cache,
             redis_cache=redis_cache,
             default_in_memory_ttl=default_in_memory_ttl,
-            default_redis_ttl=default_redis_ttl,
+            default_redis_ttl=effective_redis_ttl,
         )
         self.key_object_cache: Final = DualCache(
             in_memory_cache=key_object_in_memory_cache or InMemoryCache(),
             redis_cache=redis_cache,
             default_in_memory_ttl=default_in_memory_ttl,
-            default_redis_ttl=default_redis_ttl,
+            default_redis_ttl=effective_redis_ttl,
         )
 
     def in_memory_cache_for(self, key: str) -> InMemoryCache:
diff --git a/litellm/proxy/proxy_server.py b/litellm/proxy/proxy_server.py
index ed2a5b89a32..776f39f650d 100644
--- a/litellm/proxy/proxy_server.py
+++ b/litellm/proxy/proxy_server.py
@@ -5003,10 +5003,13 @@ def _attach_redis_usage_cache(redis_cache: RedisCache, enable_redis_auth_cache:
         default_redis_ttl=CLI_SSO_SESSION_TTL_SECONDS,
     )
     if enable_redis_auth_cache is True:
-        user_api_key_cache.attach_redis_cache(
-            redis_cache,
-            default_redis_ttl=litellm.default_redis_ttl,
-        )
+        # The auth cache mirrors its own in-memory TTL on the Redis tier (see
+        # UserApiKeyCache.__init__ and #43187). Do not pass the global
+        # default_redis_ttl here: that would override the auth cache's shorter
+        # TTL whenever default_redis_ttl is set before Redis is attached.
+        # Operators who want a longer auth-cache TTL should set
+        # general_settings.user_api_key_cache_ttl.
+        user_api_key_cache.attach_redis_cache(redis_cache)
         verbose_proxy_logger.info(
             "enable_redis_auth_cache=True: attached Redis to "
             "user_api_key_cache — virtual-key lookups are now "
diff --git a/tests/unit/caching/test_dual_cache.py b/tests/unit/caching/test_dual_cache.py
index 46600e0bf60..74c12c0c58e 100644
--- a/tests/unit/caching/test_dual_cache.py
+++ b/tests/unit/caching/test_dual_cache.py
@@ -1022,3 +1022,82 @@ async def test_async_batch_reads_of_missing_keys_hit_redis_once_per_expiry_windo
     dual_cache.last_redis_batch_access_time.update({key: time.time() - 61 for key in keys})
     await dual_cache.async_batch_get_cache(keys)
     assert redis_cache.async_batch_get_cache.await_count == 2
+
+async def _write_without_a_ttl(dual_cache: DualCache, write_path: str) -> None:
+    """One of the three write paths, called the way a caller that passes no ``ttl`` calls it."""
+    if write_path == "set_cache":
+        dual_cache.set_cache("ttl_key", "v")
+    elif write_path == "async_set_cache":
+        await dual_cache.async_set_cache("ttl_key", "v")
+    else:
+        await dual_cache.async_set_cache_pipeline([("ttl_key", "v")])
+
+
+async def _write_with_a_ttl(dual_cache: DualCache, write_path: str, ttl: float) -> None:
+    """The same three paths with an explicit ``ttl``, which must reach both tiers unchanged."""
+    if write_path == "set_cache":
+        dual_cache.set_cache("ttl_key", "v", ttl=ttl)
+    elif write_path == "async_set_cache":
+        await dual_cache.async_set_cache("ttl_key", "v", ttl=ttl)
+    else:
+        await dual_cache.async_set_cache_pipeline([("ttl_key", "v")], ttl=ttl)
+
+
+def _ttl_recording_redis() -> MagicMock:
+    """A Redis tier that records what it was written with, whichever of the two writes it uses."""
+    mock_redis = MagicMock()
+    mock_redis.async_set_cache = AsyncMock()
+    mock_redis.async_set_cache_pipeline = AsyncMock()
+    return mock_redis
+
+
+def _written_redis_ttl(mock_redis: MagicMock, write_path: str) -> object:
+    """The ttl the recording Redis tier was written with, on whichever of its writes that path uses."""
+    return getattr(mock_redis, write_path).call_args.kwargs["ttl"]
+
+
+async def _tier_ttls(
+    write_path: str, ttl: float | None
+) -> tuple[object, float]:
+    """Write one key through one path and report the Redis ttl it was written with, plus the
+    in-memory expiry. ``ttl=None`` means the caller supplied no ``ttl`` at all."""
+    in_memory_cache = InMemoryCache(default_ttl=600)
+    mock_redis = _ttl_recording_redis()
+    dual_cache = DualCache(
+        in_memory_cache=in_memory_cache,
+        redis_cache=mock_redis,
+        default_in_memory_ttl=60,
+        default_redis_ttl=3600,
+    )
+    if ttl is None:
+        await _write_without_a_ttl(dual_cache, write_path)
+    else:
+        await _write_with_a_ttl(dual_cache, write_path, ttl)
+    return _written_redis_ttl(mock_redis, write_path), in_memory_cache.ttl_dict["ttl_key"]
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("write_path", ["set_cache", "async_set_cache", "async_set_cache_pipeline"])
+async def test_dual_cache_writes_the_redis_tier_with_the_configured_default_redis_ttl(write_path: str):
+    """
+    Regression for #43187: the Redis tier was written with default_in_memory_ttl, so a configured
+    default_redis_ttl never took effect. The in-memory tier still takes its own default.
+    """
+    before = time.time()
+    written, expiry = await _tier_ttls(write_path, None)
+    after = time.time()
+
+    assert written == 3600
+    assert before + 60 <= expiry <= after + 60
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("write_path", ["set_cache", "async_set_cache", "async_set_cache_pipeline"])
+async def test_dual_cache_gives_an_explicit_ttl_to_both_tiers_unchanged(write_path: str):
+    """An explicit ``ttl`` still overrides both tier defaults rather than being replaced by them."""
+    before = time.time()
+    written, expiry = await _tier_ttls(write_path, 99.0)
+    after = time.time()
+
+    assert written == 99.0
+    assert before + 99 <= expiry <= after + 99
diff --git a/tests/unit/caching/test_request_redis_batch_pre_call.py b/tests/unit/caching/test_request_redis_batch_pre_call.py
index cee7bfd8c65..69f7a58deee 100644
--- a/tests/unit/caching/test_request_redis_batch_pre_call.py
+++ b/tests/unit/caching/test_request_redis_batch_pre_call.py
@@ -1054,6 +1054,19 @@ async def test_a_pipelined_management_write_without_a_ttl_expires_in_redis_like_
     assert [(c[0], c[1], c[3]) for c in client.pipelines[0].commands] == [("SET", "team_id:t1", 5)]
 
 
+@pytest.mark.asyncio
+async def test_a_pipelined_write_without_a_ttl_uses_the_configured_default_redis_ttl():
+    """Regression for #43187: the pipelined Redis SET was written with default_in_memory_ttl, so a
+    configured default_redis_ttl never reached it."""
+    client = FakeClient(_lua_ok_replies)
+    redis_cache = FakeRedisCache(client)
+    cache = DualCache(redis_cache=redis_cache, default_in_memory_ttl=5, default_redis_ttl=3600)
+    with request_redis_batch_scope() as request:
+        await cache.async_set_cache_pre_call("k1", {"v": 1}, None)
+        await request.flush_all()
+    assert [(c[0], c[1], c[3]) for c in client.pipelines[0].commands] == [("SET", "k1", 3600)]
+
+
 @pytest.mark.asyncio
 async def test_identity_prefetch_is_one_mget_after_which_hits_and_misses_alike_cost_no_read():
     client = FakeClient(replies)
diff --git a/tests/unit/proxy/test_redis_auth_cache_flag.py b/tests/unit/proxy/test_redis_auth_cache_flag.py
index cb600bbb5fd..a2ce7a1028d 100644
--- a/tests/unit/proxy/test_redis_auth_cache_flag.py
+++ b/tests/unit/proxy/test_redis_auth_cache_flag.py
@@ -191,3 +191,27 @@ class TestRedisAuthCacheFlag:
             ps._attach_redis_usage_cache(fake_redis, enable_redis_auth_cache=False)
             assert limiter_cache.redis_cache is fake_redis
             assert ps.user_api_key_cache.redis_cache is None
+
+def test_auth_cache_redis_tier_keeps_in_memory_ttl_when_default_redis_ttl_is_set(monkeypatch):
+    """
+    #43187: user_api_key_cache mirrors its in-memory TTL on Redis. A global
+    default_redis_ttl, from litellm_settings or cache_params, must not override
+    that when Redis is attached.
+    """
+    from types import SimpleNamespace
+
+    from litellm.proxy.common_utils.user_api_key_cache import UserApiKeyCache
+
+    monkeypatch.setattr(litellm, "default_redis_ttl", 3600)
+    auth_cache = UserApiKeyCache(default_in_memory_ttl=60)
+    with (
+        patch.object(ps, "user_api_key_cache", auth_cache),
+        patch.object(ps, "spend_counter_cache", DualCache()),
+        patch.object(ps, "cli_sso_session_cache", DualCache()),
+        patch.object(ps, "litellm_config_cache", SimpleNamespace(redis_cache=None)),
+    ):
+        ps._attach_redis_usage_cache(_FakeRedisCache(), enable_redis_auth_cache=True)
+
+    assert auth_cache.redis_cache is not None
+    assert auth_cache.default_redis_ttl == 60
+    assert auth_cache.key_object_cache.default_redis_ttl == 60