diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1aa4be4..9d88a8f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,8 +4,36 @@ All notable changes to kalshi-sdk will be documented in this file.
 
 ## [Unreleased]
 
+### Fixed
+
+- **`/account/limits` response now parses against the live server.** The
+  published OpenAPI spec (v3.13.0) declares `read_limit`/`write_limit` as
+  ints, but the live API returns nested `read`/`write` token-bucket objects
+  with `bucket_capacity` + `refill_rate`. `AccountApiLimits` now matches the
+  server. New `RateLimit` model exposed for the bucket structure.
+- **`/search/tags_by_categories` no longer crashes** when a category (e.g.
+  `Social`) returns `null` instead of an empty list. `tags_by_categories`
+  values are now `NullableList[str]`, collapsing `null` → `[]`.
+
 ### Breaking
 
+- **`AccountApiLimits.read_limit` / `.write_limit` removed.** Replaced with
+  `AccountApiLimits.read` / `.write`, both of type `RateLimit`
+  (`bucket_capacity: int`, `refill_rate: int`). The previous int fields
+  never worked against the live server, so practical migration impact is
+  expected to be limited to code written from the spec rather than tested
+  against the API.
+
+  ```python
+  # Before
+  limits = client.account.limits()
+  limits.read_limit   # AttributeError after upgrade
+
+  # After
+  limits.read.bucket_capacity   # int
+  limits.read.refill_rate       # int
+  ```
+
 - **`Order.type` renamed to `Order.order_type`.** Wire format is unchanged
   (`validation_alias=AliasChoices("type", "order_type")` accepts both names on
   deserialization), but any user code reading `.type` on an `Order` instance
diff --git a/kalshi/__init__.py b/kalshi/__init__.py
index 3b2fd33..35d99c8 100644
--- a/kalshi/__init__.py
+++ b/kalshi/__init__.py
@@ -111,6 +111,7 @@
     PositionsResponse,
     PriceDistribution,
     Quote,
+    RateLimit,
     Schedule,
     ScopeList,
     SelfTradePreventionTypeLiteral,
@@ -246,6 +247,7 @@
     "PositionsResponse",
     "PriceDistribution",
     "Quote",
+    "RateLimit",
     "Schedule",
     "ScopeList",
     "SelfTradePreventionTypeLiteral",
diff --git a/kalshi/_contract_map.py b/kalshi/_contract_map.py
index ca1c5a3..3ddf009 100644
--- a/kalshi/_contract_map.py
+++ b/kalshi/_contract_map.py
@@ -210,7 +210,11 @@ class ContractEntry:
     ContractEntry(
         sdk_model="kalshi.models.account.AccountApiLimits",
         spec_schema="GetAccountApiLimitsResponse",
-        notes="Spec wraps tier/read/write limits in GetAccountApiLimitsResponse",
+        notes=(
+            "SPEC DRIFT: spec declares int 'read_limit'/'write_limit' but the "
+            "live server returns nested 'read'/'write' token-bucket objects. "
+            "SDK model follows the server."
+        ),
     ),
     ContractEntry(
         sdk_model="kalshi.models.structured_targets.StructuredTarget",
diff --git a/kalshi/models/__init__.py b/kalshi/models/__init__.py
index 3fc6c6d..1e627e4 100644
--- a/kalshi/models/__init__.py
+++ b/kalshi/models/__init__.py
@@ -1,6 +1,6 @@
 """Kalshi SDK data models."""
 
-from kalshi.models.account import AccountApiLimits
+from kalshi.models.account import AccountApiLimits, RateLimit
 from kalshi.models.api_keys import (
     ApiKey,
     CreateApiKeyRequest,
@@ -238,6 +238,7 @@
     "PositionsResponse",
     "PriceDistribution",
     "Quote",
+    "RateLimit",
     "Schedule",
     "ScopeList",
     "SelfTradePreventionTypeLiteral",
diff --git a/kalshi/models/account.py b/kalshi/models/account.py
index 8a8f583..566861f 100644
--- a/kalshi/models/account.py
+++ b/kalshi/models/account.py
@@ -5,16 +5,31 @@
 from pydantic import BaseModel
 
 
+class RateLimit(BaseModel):
+    """Per-direction (read/write) token-bucket rate limit.
+
+    The server enforces a token bucket per direction: ``bucket_capacity``
+    tokens are allowed in a burst; ``refill_rate`` tokens are added per
+    second up to the cap. Requests above the cap return 429.
+    """
+
+    bucket_capacity: int
+    refill_rate: int
+
+    model_config = {"extra": "allow"}
+
+
 class AccountApiLimits(BaseModel):
     """Rate limits associated with the authenticated user's API tier.
 
-    ``read_limit`` and ``write_limit`` are requests-per-second ceilings
-    the server will enforce before returning 429. ``usage_tier`` is a
-    human-readable label (e.g., ``standard``, ``elevated``).
+    NOTE: The published OpenAPI spec (v3.13.0) declares ``read_limit`` and
+    ``write_limit`` as ints, but the live server returns nested token-bucket
+    objects under ``read`` and ``write``. The SDK matches the server. If the
+    spec is corrected upstream, the contract-drift test will flag it.
     """
 
     usage_tier: str
-    read_limit: int
-    write_limit: int
+    read: RateLimit
+    write: RateLimit
 
     model_config = {"extra": "allow"}
diff --git a/kalshi/models/search.py b/kalshi/models/search.py
index 363475d..cd09dee 100644
--- a/kalshi/models/search.py
+++ b/kalshi/models/search.py
@@ -40,9 +40,14 @@ class SportFilterDetails(BaseModel):
 
 
 class GetTagsForSeriesCategoriesResponse(BaseModel):
-    """Response from GET /search/tags_by_categories."""
+    """Response from GET /search/tags_by_categories.
 
-    tags_by_categories: dict[str, list[str]] = {}
+    NullableList collapses server-side nulls into empty lists, so consumers
+    can always iterate ``tags_by_categories[category]`` without a None check.
+    Observed in the wild: the ``Social`` category currently returns null.
+    """
+
+    tags_by_categories: dict[str, NullableList[str]] = {}
 
     model_config = {"extra": "allow"}
 
diff --git a/tests/integration/test_account.py b/tests/integration/test_account.py
index 0365351..b2065a2 100644
--- a/tests/integration/test_account.py
+++ b/tests/integration/test_account.py
@@ -19,8 +19,10 @@ def test_limits(self, sync_client: KalshiClient) -> None:
         result = sync_client.account.limits()
         assert isinstance(result, AccountApiLimits)
         assert_model_fields(result)
-        assert result.read_limit >= 0
-        assert result.write_limit >= 0
+        assert result.read.bucket_capacity > 0
+        assert result.read.refill_rate > 0
+        assert result.write.bucket_capacity > 0
+        assert result.write.refill_rate > 0
         assert result.usage_tier
 
 
diff --git a/tests/test_account.py b/tests/test_account.py
index 7515cbc..64dfcf2 100644
--- a/tests/test_account.py
+++ b/tests/test_account.py
@@ -52,15 +52,17 @@ def test_returns_limits(self, account: AccountResource) -> None:
                 200,
                 json={
                     "usage_tier": "standard",
-                    "read_limit": 100,
-                    "write_limit": 10,
+                    "read": {"bucket_capacity": 200, "refill_rate": 100},
+                    "write": {"bucket_capacity": 20, "refill_rate": 10},
                 },
             )
         )
         limits = account.limits()
         assert limits.usage_tier == "standard"
-        assert limits.read_limit == 100
-        assert limits.write_limit == 10
+        assert limits.read.bucket_capacity == 200
+        assert limits.read.refill_rate == 100
+        assert limits.write.bucket_capacity == 20
+        assert limits.write.refill_rate == 10
 
     def test_requires_auth(self, unauth_account: AccountResource) -> None:
         with pytest.raises(AuthRequiredError):
@@ -86,15 +88,17 @@ async def test_returns_limits(
                 200,
                 json={
                     "usage_tier": "elevated",
-                    "read_limit": 500,
-                    "write_limit": 50,
+                    "read": {"bucket_capacity": 1000, "refill_rate": 500},
+                    "write": {"bucket_capacity": 100, "refill_rate": 50},
                 },
             )
         )
         limits = await async_account.limits()
         assert limits.usage_tier == "elevated"
-        assert limits.read_limit == 500
-        assert limits.write_limit == 50
+        assert limits.read.bucket_capacity == 1000
+        assert limits.read.refill_rate == 500
+        assert limits.write.bucket_capacity == 100
+        assert limits.write.refill_rate == 50
 
     @pytest.mark.asyncio
     async def test_requires_auth(