diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3ebb564..0ca380b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,16 @@ All notable changes to the `fipsagents` package will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/).
 
+## [0.14.2] - 2026-04-28
+
+### Added
+
+- **`HttpSessionStore.get_cost_data` reads from the platform.** Replaces the `NotImplementedError` placeholder with a real `GET /v1/sessions/{id}/cost_data`, closing the cumulative-cost gap noted in 0.14.0's release notes. HTTP-backed deployments now get the same cumulative shallow-merge semantics that SQLite/Postgres provide natively — the per-turn accumulator on `OpenAIChatServer` reads existing totals before computing the merge, so multi-turn sessions converge on cumulative numbers instead of last-write-wins. 5 new tests across the unit and e2e suites; total `fipsagents` suite 765 → 770.
+
+### Notes
+
+- Requires `fipsagents-platform>=0.2.1`. Older platforms 404 cleanly on the read path and the agent degrades to the previous last-write-wins behavior — same operational shape as 0.14.0/0.14.1, no breakage.
+
 ## [0.14.1] - 2026-04-27
 
 ### Fixed
diff --git a/packages/fipsagents/pyproject.toml b/packages/fipsagents/pyproject.toml
index a53ceff..24ec51d 100644
--- a/packages/fipsagents/pyproject.toml
+++ b/packages/fipsagents/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "fipsagents"
-version = "0.14.1"
+version = "0.14.2"
 description = "Production-ready AI agent framework for FIPS/OpenShift environments"
 readme = "README.md"
 license = {file = "LICENSE"}
diff --git a/packages/fipsagents/src/fipsagents/server/http.py b/packages/fipsagents/src/fipsagents/server/http.py
index 6a2debb..592f256 100644
--- a/packages/fipsagents/src/fipsagents/server/http.py
+++ b/packages/fipsagents/src/fipsagents/server/http.py
@@ -252,17 +252,19 @@ async def update(
         return status != 404
 
     async def get_cost_data(self, session_id: str) -> dict:
-        # The platform service has no GET /v1/sessions/{id}/cost_data
-        # endpoint yet. Until it does, callers must treat the HTTP
-        # backend as write-only for cost accumulator state. The server's
-        # per-turn accumulator catches NotImplementedError and treats
-        # the existing total as empty (so the next write is the turn's
-        # delta rather than a true cumulative). A follow-up issue tracks
-        # exposing the read endpoint on the platform.
-        raise NotImplementedError(
-            "HttpSessionStore.get_cost_data: the platform service does "
-            "not expose a GET endpoint for cost_data yet."
+        # Mirrors the SQLite/Postgres contract: empty dict when the
+        # session is missing or has no cost_data yet. Requires
+        # fipsagents-platform >= 0.2.1 (which exposes the GET endpoint);
+        # against older platforms the route 404s on every call and we
+        # degrade gracefully to last-write-wins semantics.
+        status, data = await self._client.request(
+            "GET",
+            f"/v1/sessions/{session_id}/cost_data",
+            not_found_returns_none=True,
         )
+        if status == 404 or data is None:
+            return {}
+        return data.get("cost_data") or {}
 
     async def delete(self, session_id: str) -> bool:
         status, _ = await self._client.request(
diff --git a/packages/fipsagents/tests/test_http_stores.py b/packages/fipsagents/tests/test_http_stores.py
index de2010e..33c46db 100644
--- a/packages/fipsagents/tests/test_http_stores.py
+++ b/packages/fipsagents/tests/test_http_stores.py
@@ -221,17 +221,41 @@ async def test_session_update_none_cost_data_delegates_to_exists() -> None:
 
 
 @pytest.mark.asyncio
-async def test_session_get_cost_data_raises_not_implemented() -> None:
-    """The HTTP backend has no GET cost_data endpoint yet -- raise so the
-    server-side accumulator can fall back to a delta-only write."""
-    rec = _Recorder([])
+async def test_session_get_cost_data_returns_dict() -> None:
+    """GET /v1/sessions/{id}/cost_data parses the cumulative dict."""
+    rec = _Recorder([_ok(200, {
+        "session_id": "sess_abc",
+        "cost_data": {"input_tokens": 100, "output_tokens": 50},
+    })])
+    store = HttpSessionStore(
+        "http://platform.test", transport=httpx.MockTransport(rec),
+    )
+    result = await store.get_cost_data("sess_abc")
+    assert result == {"input_tokens": 100, "output_tokens": 50}
+    assert rec.requests[0].method == "GET"
+    assert rec.requests[0].url.path == "/v1/sessions/sess_abc/cost_data"
+    await store.close()
+
+
+@pytest.mark.asyncio
+async def test_session_get_cost_data_404_returns_empty() -> None:
+    """Missing sessions degrade to {} per the ABC contract."""
+    rec = _Recorder([_ok(404, {"detail": "not found"})])
+    store = HttpSessionStore(
+        "http://platform.test", transport=httpx.MockTransport(rec),
+    )
+    assert await store.get_cost_data("missing") == {}
+    await store.close()
+
+
+@pytest.mark.asyncio
+async def test_session_get_cost_data_empty_dict_round_trips() -> None:
+    """Existing session with no writes returns the platform's empty dict."""
+    rec = _Recorder([_ok(200, {"session_id": "sess_empty", "cost_data": {}})])
     store = HttpSessionStore(
         "http://platform.test", transport=httpx.MockTransport(rec),
     )
-    with pytest.raises(NotImplementedError):
-        await store.get_cost_data("sess_anything")
-    # No HTTP request should have been issued.
-    assert rec.requests == []
+    assert await store.get_cost_data("sess_empty") == {}
     await store.close()
 
 
diff --git a/packages/fipsagents/tests/test_http_stores_e2e.py b/packages/fipsagents/tests/test_http_stores_e2e.py
index 2524e00..f79af93 100644
--- a/packages/fipsagents/tests/test_http_stores_e2e.py
+++ b/packages/fipsagents/tests/test_http_stores_e2e.py
@@ -174,6 +174,31 @@ async def test_session_update_none_cost_data_returns_existence(
     await store.close()
 
 
+@pytest.mark.asyncio
+async def test_session_get_cost_data_round_trip(platform_transport) -> None:
+    """Two PATCHes then GET — the returned dict is the cumulative merge."""
+    store = HttpSessionStore(
+        "http://platform.test", transport=platform_transport,
+    )
+    sid = await store.create("sess_e2e_get_cost")
+    await store.update(sid, cost_data={"input_tokens": 10, "output_tokens": 5})
+    await store.update(sid, cost_data={"input_tokens": 30, "requests": 2})
+
+    result = await store.get_cost_data(sid)
+    assert result == {"input_tokens": 30, "output_tokens": 5, "requests": 2}
+    await store.close()
+
+
+@pytest.mark.asyncio
+async def test_session_get_cost_data_missing_returns_empty(platform_transport) -> None:
+    """Platform 404 → ABC-compliant empty dict on the agent side."""
+    store = HttpSessionStore(
+        "http://platform.test", transport=platform_transport,
+    )
+    assert await store.get_cost_data("sess_e2e_never_existed") == {}
+    await store.close()
+
+
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