diff --git a/CHANGELOG.md b/CHANGELOG.md
index 515a1a4..4be9da3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,13 @@ All notable changes to kalshi-sdk will be documented in this file.
 
 ### Changed
 
+- **All response models uniformly use `extra="allow"` (#114).** Previously
+  5 response models (`Page`, `Orderbook`, `OrderbookLevel`,
+  `BidAskDistribution`, `PriceDistribution`) fell back to Pydantic's default
+  `extra="ignore"`, silently dropping unknown fields — while the 80 sibling
+  response models exposed them via `__pydantic_extra__`. Instances of those
+  5 classes will now preserve unknown fields. Request bodies remain
+  `extra="forbid"` (unchanged).
 - **Count/size/volume response fields retyped from `DollarDecimal` to
   `FixedPointCount` (#90).** Fields with `_fp` wire aliases were annotated
   as `DollarDecimal` — the type that signals "dollar amount." Runtime
diff --git a/kalshi/models/common.py b/kalshi/models/common.py
index 91940a1..f5cd369 100644
--- a/kalshi/models/common.py
+++ b/kalshi/models/common.py
@@ -29,6 +29,7 @@ class Page(BaseModel, Generic[T]):
 
     items: list[T]
     cursor: str | None = None
+    model_config = {"extra": "allow"}
 
     @property
     def has_next(self) -> bool:
diff --git a/kalshi/models/markets.py b/kalshi/models/markets.py
index 64cbd8d..b50561b 100644
--- a/kalshi/models/markets.py
+++ b/kalshi/models/markets.py
@@ -148,6 +148,8 @@ class OrderbookLevel(BaseModel):
     price: DollarDecimal
     quantity: FixedPointCount
 
+    model_config = {"extra": "allow"}
+
 
 class Orderbook(BaseModel):
     """Orderbook for a market."""
@@ -156,6 +158,8 @@ class Orderbook(BaseModel):
     yes: NullableList[OrderbookLevel] = []
     no: NullableList[OrderbookLevel] = []
 
+    model_config = {"extra": "allow"}
+
 
 class BidAskDistribution(BaseModel):
     """OHLC data for bid/ask prices within a candlestick period."""
@@ -177,7 +181,7 @@ class BidAskDistribution(BaseModel):
         validation_alias=AliasChoices("close_dollars", "close"),
     )
 
-    model_config = {"populate_by_name": True}
+    model_config = {"extra": "allow", "populate_by_name": True}
 
 
 class PriceDistribution(BaseModel):
@@ -203,7 +207,7 @@ class PriceDistribution(BaseModel):
         validation_alias=AliasChoices("close_dollars", "close"),
     )
 
-    model_config = {"populate_by_name": True}
+    model_config = {"extra": "allow", "populate_by_name": True}
 
 
 class Candlestick(BaseModel):
diff --git a/tests/test_model_extra_policy.py b/tests/test_model_extra_policy.py
new file mode 100644
index 0000000..adbf6e6
--- /dev/null
+++ b/tests/test_model_extra_policy.py
@@ -0,0 +1,69 @@
+"""Enforce a uniform ``extra=`` policy across response models (#114).
+
+Response models use ``extra="allow"`` so the SDK is forwards-compatible when
+Kalshi adds new fields. Request bodies use ``extra="forbid"`` so the
+client-side phantom-key check catches user typos at call time.
+"""
+
+from __future__ import annotations
+
+import pytest
+from pydantic import BaseModel
+
+import kalshi.models
+
+# Request bodies must stay `extra="forbid"`. Identified by name suffix per
+# the CLAUDE.md "Adding a new resource" convention. Both `Request` and the
+# longer `RequestOrder` are needed: `BatchCancelOrdersRequestOrder` is a
+# request-body sub-model whose name doesn't end in plain `Request`.
+_REQUEST_BODY_SUFFIXES = ("Request", "RequestOrder")
+
+
+def _exported_model_classes() -> list[tuple[str, type[BaseModel]]]:
+    """Every BaseModel subclass re-exported from ``kalshi.models.__all__``.
+
+    Scope assumption: this only enforces the policy on models exported via
+    ``__all__``. A response model defined in a ``models/*.py`` file but
+    never wired into ``__all__`` would silently escape the check. The
+    project convention is to export every model; new models added without
+    exporting them fall outside this guard by design.
+    """
+    out: list[tuple[str, type[BaseModel]]] = []
+    for name in sorted(kalshi.models.__all__):
+        obj = getattr(kalshi.models, name)
+        if isinstance(obj, type) and issubclass(obj, BaseModel):
+            out.append((name, obj))
+    return out
+
+
+def _is_request_body(name: str) -> bool:
+    return any(name.endswith(suffix) for suffix in _REQUEST_BODY_SUFFIXES)
+
+
+_ALL_MODELS = _exported_model_classes()
+_RESPONSE_MODELS = [(n, c) for n, c in _ALL_MODELS if not _is_request_body(n)]
+_REQUEST_MODELS = [(n, c) for n, c in _ALL_MODELS if _is_request_body(n)]
+
+
+@pytest.mark.parametrize(
+    "name,cls", _RESPONSE_MODELS, ids=[n for n, _ in _RESPONSE_MODELS],
+)
+def test_response_models_use_extra_allow(name: str, cls: type[BaseModel]) -> None:
+    cfg = getattr(cls, "model_config", {})
+    extra = cfg.get("extra")
+    assert extra == "allow", (
+        f"Response model {name} has extra={extra!r}; expected 'allow' so the "
+        f"SDK is forwards-compatible when Kalshi adds new fields (#114)."
+    )
+
+
+@pytest.mark.parametrize(
+    "name,cls", _REQUEST_MODELS, ids=[n for n, _ in _REQUEST_MODELS],
+)
+def test_request_bodies_use_extra_forbid(name: str, cls: type[BaseModel]) -> None:
+    cfg = getattr(cls, "model_config", {})
+    extra = cfg.get("extra")
+    assert extra == "forbid", (
+        f"Request body {name} has extra={extra!r}; expected 'forbid' so "
+        f"phantom kwargs fail at call time (CLAUDE.md key convention)."
+    )