diff --git a/contract-tests/data-model/include/data_model/data_model.hpp b/contract-tests/data-model/include/data_model/data_model.hpp
index 679fd0015..83816623f 100644
--- a/contract-tests/data-model/include/data_model/data_model.hpp
+++ b/contract-tests/data-model/include/data_model/data_model.hpp
@@ -150,6 +150,21 @@ struct ConfigWrapper {
 
 NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(ConfigWrapper, name, version);
 
+struct ConfigBigSegmentsParams {
+    std::string callbackUri;
+    std::optional<uint32_t> userCacheSize;
+    std::optional<uint64_t> userCacheTimeMs;
+    std::optional<uint64_t> statusPollIntervalMs;
+    std::optional<uint64_t> staleAfterMs;
+};
+
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(ConfigBigSegmentsParams,
+                                                callbackUri,
+                                                userCacheSize,
+                                                userCacheTimeMs,
+                                                statusPollIntervalMs,
+                                                staleAfterMs);
+
 struct ConfigParams {
     std::string credential;
     std::optional<uint32_t> startWaitTimeMs;
@@ -164,6 +179,7 @@ struct ConfigParams {
     std::optional<ConfigProxyParams> proxy;
     std::optional<ConfigHooksParams> hooks;
     std::optional<ConfigWrapper> wrapper;
+    std::optional<ConfigBigSegmentsParams> bigSegments;
 };
 
 NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(ConfigParams,
@@ -179,7 +195,8 @@ NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(ConfigParams,
                                                 tls,
                                                 proxy,
                                                 hooks,
-                                                wrapper);
+                                                wrapper,
+                                                bigSegments);
 
 struct ContextSingleParams {
     std::optional<std::string> kind;
@@ -328,6 +345,15 @@ struct IdentifyEventParams {
 
 NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(IdentifyEventParams, context);
 
+struct BigSegmentStoreStatusResponse {
+    bool available;
+    bool stale;
+};
+
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(BigSegmentStoreStatusResponse,
+                                                available,
+                                                stale);
+
 enum class Command {
     Unknown = -1,
     EvaluateFlag,
@@ -336,7 +362,8 @@ enum class Command {
     CustomEvent,
     FlushEvents,
     ContextBuild,
-    ContextConvert
+    ContextConvert,
+    GetBigSegmentStoreStatus
 };
 
 NLOHMANN_JSON_SERIALIZE_ENUM(Command,
@@ -347,7 +374,9 @@ NLOHMANN_JSON_SERIALIZE_ENUM(Command,
                               {Command::CustomEvent, "customEvent"},
                               {Command::FlushEvents, "flushEvents"},
                               {Command::ContextBuild, "contextBuild"},
-                              {Command::ContextConvert, "contextConvert"}});
+                              {Command::ContextConvert, "contextConvert"},
+                              {Command::GetBigSegmentStoreStatus,
+                               "getBigSegmentStoreStatus"}});
 
 struct CommandParams {
     Command command;
diff --git a/contract-tests/server-contract-tests/CMakeLists.txt b/contract-tests/server-contract-tests/CMakeLists.txt
index 9455cd27e..000dea286 100644
--- a/contract-tests/server-contract-tests/CMakeLists.txt
+++ b/contract-tests/server-contract-tests/CMakeLists.txt
@@ -17,6 +17,7 @@ add_executable(server-tests
         src/entity_manager.cpp
         src/client_entity.cpp
         src/contract_test_hook.cpp
+        src/contract_test_big_segment_store.cpp
         )
 
 target_link_libraries(server-tests PRIVATE
diff --git a/contract-tests/server-contract-tests/include/client_entity.hpp b/contract-tests/server-contract-tests/include/client_entity.hpp
index 39b4a3be3..f62c7f2a6 100644
--- a/contract-tests/server-contract-tests/include/client_entity.hpp
+++ b/contract-tests/server-contract-tests/include/client_entity.hpp
@@ -27,6 +27,8 @@ class ClientEntity {
 
     tl::expected<nlohmann::json, std::string> Custom(CustomEventParams const&);
 
+    tl::expected<nlohmann::json, std::string> GetBigSegmentStoreStatus();
+
     std::unique_ptr<launchdarkly::server_side::Client> client_;
 };
 
diff --git a/contract-tests/server-contract-tests/include/contract_test_big_segment_store.hpp b/contract-tests/server-contract-tests/include/contract_test_big_segment_store.hpp
new file mode 100644
index 000000000..5c1d3a58f
--- /dev/null
+++ b/contract-tests/server-contract-tests/include/contract_test_big_segment_store.hpp
@@ -0,0 +1,39 @@
+#pragma once
+
+#include <launchdarkly/server_side/integrations/big_segments/ibig_segment_store.hpp>
+
+#include <nlohmann/json.hpp>
+
+#include <tl/expected.hpp>
+
+#include <string>
+
+/**
+ * A Big Segment store that delegates membership and metadata lookups to the
+ * contract-test harness over HTTP, mirroring how ContractTestHook posts to the
+ * harness. Each lookup is a synchronous request/response (unlike the hook's
+ * fire-and-forget) because IBigSegmentStore must return the result.
+ *
+ * Thread-safe: holds only the immutable callback URI and performs each request
+ * on its own local io_context.
+ */
+class ContractTestBigSegmentStore
+    : public launchdarkly::server_side::integrations::IBigSegmentStore {
+   public:
+    explicit ContractTestBigSegmentStore(std::string callback_uri);
+
+    [[nodiscard]] GetMembershipResult GetMembership(
+        std::string const& context_hash) const noexcept override;
+
+    [[nodiscard]] GetMetadataResult GetMetadata() const noexcept override;
+
+   private:
+    // Synchronous POST of `body` to `<callback_uri><path>`. Returns the parsed
+    // JSON response on HTTP 200, or an error string (non-200 body, transport
+    // failure, or parse failure).
+    [[nodiscard]] tl::expected<nlohmann::json, std::string> Post(
+        std::string const& path,
+        nlohmann::json const& body) const noexcept;
+
+    std::string const callback_uri_;
+};
diff --git a/contract-tests/server-contract-tests/src/client_entity.cpp b/contract-tests/server-contract-tests/src/client_entity.cpp
index 4fc220307..9cd5c2f86 100644
--- a/contract-tests/server-contract-tests/src/client_entity.cpp
+++ b/contract-tests/server-contract-tests/src/client_entity.cpp
@@ -4,10 +4,10 @@
 #include <boost/json.hpp>
 
 #include <launchdarkly/context_builder.hpp>
-#include <launchdarkly/serialization/json_context.hpp>
-#include <launchdarkly/serialization/json_evaluation_reason.hpp>
 #include <launchdarkly/detail/serialization/json_primitives.hpp>
 #include <launchdarkly/detail/serialization/json_value.hpp>
+#include <launchdarkly/serialization/json_context.hpp>
+#include <launchdarkly/serialization/json_evaluation_reason.hpp>
 #include <launchdarkly/server_side/serialization/json_all_flags_state.hpp>
 #include <launchdarkly/value.hpp>
 
@@ -172,6 +172,15 @@ tl::expected<nlohmann::json, std::string> ClientEntity::Custom(
     return nlohmann::json{};
 }
 
+tl::expected<nlohmann::json, std::string>
+ClientEntity::GetBigSegmentStoreStatus() {
+    auto status = client_->BigSegmentStoreStatus().Status();
+    BigSegmentStoreStatusResponse resp{};
+    resp.available = status.IsAvailable();
+    resp.stale = status.IsStale();
+    return resp;
+}
+
 tl::expected<nlohmann::json, std::string> ClientEntity::EvaluateAll(
     EvaluateAllFlagParams const& params) {
     EvaluateAllFlagsResponse resp{};
@@ -388,6 +397,8 @@ tl::expected<nlohmann::json, std::string> ClientEntity::Command(
                 return tl::make_unexpected("contextConvert params must be set");
             }
             return ContextConvert(*params.contextConvert);
+        case Command::GetBigSegmentStoreStatus:
+            return GetBigSegmentStoreStatus();
     }
     return tl::make_unexpected("unrecognized command");
 }
diff --git a/contract-tests/server-contract-tests/src/contract_test_big_segment_store.cpp b/contract-tests/server-contract-tests/src/contract_test_big_segment_store.cpp
new file mode 100644
index 000000000..13dd6181e
--- /dev/null
+++ b/contract-tests/server-contract-tests/src/contract_test_big_segment_store.cpp
@@ -0,0 +1,121 @@
+#include "contract_test_big_segment_store.hpp"
+
+#include <boost/asio/connect.hpp>
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/ip/tcp.hpp>
+#include <boost/beast/core.hpp>
+#include <boost/beast/http.hpp>
+#include <boost/url.hpp>
+
+#include <chrono>
+#include <optional>
+#include <utility>
+#include <vector>
+
+namespace beast = boost::beast;
+namespace http = beast::http;
+namespace net = boost::asio;
+using tcp = net::ip::tcp;
+
+using namespace launchdarkly::server_side::integrations;
+
+ContractTestBigSegmentStore::ContractTestBigSegmentStore(
+    std::string callback_uri)
+    : callback_uri_(std::move(callback_uri)) {}
+
+tl::expected<nlohmann::json, std::string> ContractTestBigSegmentStore::Post(
+    std::string const& path,
+    nlohmann::json const& body) const noexcept {
+    try {
+        auto uri_result = boost::urls::parse_uri(callback_uri_);
+        if (!uri_result) {
+            return tl::make_unexpected("invalid callback URI: " +
+                                       callback_uri_);
+        }
+        auto uri = *uri_result;
+        std::string const host(uri.host());
+        std::string const port =
+            uri.has_port() ? std::string(uri.port()) : "80";
+        std::string base(uri.path());
+        // The callback URI carries a base path; the sub-path (/getMembership,
+        // /getMetadata) is appended. Drop any trailing slash to avoid "//".
+        if (!base.empty() && base.back() == '/') {
+            base.pop_back();
+        }
+        std::string const target = base + path;
+
+        net::io_context ioc;
+        tcp::resolver resolver(ioc);
+        beast::tcp_stream stream(ioc);
+        stream.connect(resolver.resolve(host, port));
+
+        http::request<http::string_body> req{http::verb::post, target, 11};
+        req.set(http::field::host, host);
+        req.set(http::field::user_agent, "cpp-server-sdk-contract-tests");
+        req.set(http::field::content_type, "application/json");
+        req.body() = body.dump();
+        req.prepare_payload();
+        http::write(stream, req);
+
+        beast::flat_buffer buffer;
+        http::response<http::string_body> res;
+        http::read(stream, buffer, res);
+
+        beast::error_code ec;
+        stream.socket().shutdown(tcp::socket::shutdown_both, ec);
+
+        if (res.result_int() != 200) {
+            return tl::make_unexpected(res.body());
+        }
+        return nlohmann::json::parse(res.body());
+    } catch (std::exception const& e) {
+        return tl::make_unexpected(e.what());
+    }
+}
+
+ContractTestBigSegmentStore::GetMembershipResult
+ContractTestBigSegmentStore::GetMembership(
+    std::string const& context_hash) const noexcept {
+    auto result = Post("/getMembership", {{"contextHash", context_hash}});
+    if (!result) {
+        return tl::make_unexpected(result.error());
+    }
+    try {
+        std::vector<std::string> included;
+        std::vector<std::string> excluded;
+        auto const it = result->find("values");
+        if (it != result->end() && it->is_object()) {
+            for (auto const& [segment_ref, member] : it->items()) {
+                (member.get<bool>() ? included : excluded)
+                    .push_back(segment_ref);
+            }
+        }
+        return Membership::FromSegmentRefs(included, excluded);
+    } catch (std::exception const& e) {
+        return tl::make_unexpected(e.what());
+    }
+}
+
+ContractTestBigSegmentStore::GetMetadataResult
+ContractTestBigSegmentStore::GetMetadata() const noexcept {
+    auto result = Post("/getMetadata", nlohmann::json::object());
+    if (!result) {
+        return tl::make_unexpected(result.error());
+    }
+    try {
+        auto const it = result->find("lastUpToDate");
+        // Absent or zero means the store has never been synchronized.
+        if (it == result->end() || it->is_null()) {
+            return std::optional<StoreMetadata>{std::nullopt};
+        }
+        auto const millis = it->get<std::uint64_t>();
+        if (millis == 0) {
+            return std::optional<StoreMetadata>{std::nullopt};
+        }
+        return std::optional<StoreMetadata>{
+            StoreMetadata{std::chrono::system_clock::time_point{
+                std::chrono::milliseconds{millis}}}};
+    } catch (std::exception const& e) {
+        return tl::make_unexpected(e.what());
+    }
+}
diff --git a/contract-tests/server-contract-tests/src/entity_manager.cpp b/contract-tests/server-contract-tests/src/entity_manager.cpp
index 085df1c2d..f839dd78c 100644
--- a/contract-tests/server-contract-tests/src/entity_manager.cpp
+++ b/contract-tests/server-contract-tests/src/entity_manager.cpp
@@ -1,8 +1,10 @@
 #include "entity_manager.hpp"
+#include "contract_test_big_segment_store.hpp"
 #include "contract_test_hook.hpp"
 
 #include <launchdarkly/context_builder.hpp>
 #include <launchdarkly/serialization/json_context.hpp>
+#include <launchdarkly/server_side/config/builders/big_segments_builder.hpp>
 #include <launchdarkly/server_side/config/config_builder.hpp>
 
 #include <boost/json.hpp>
@@ -140,7 +142,8 @@ std::optional<std::string> EntityManager::create(ConfigParams const& in) {
 
     if (in.hooks) {
         for (auto const& hook_config : in.hooks->hooks) {
-            auto hook = std::make_shared<ContractTestHook>(executor_, hook_config);
+            auto hook =
+                std::make_shared<ContractTestHook>(executor_, hook_config);
             config_builder.Hooks(hook);
         }
     }
@@ -154,6 +157,28 @@ std::optional<std::string> EntityManager::create(ConfigParams const& in) {
         }
     }
 
+    if (in.bigSegments) {
+        auto store = std::make_shared<ContractTestBigSegmentStore>(
+            in.bigSegments->callbackUri);
+        auto big_segments = config::builders::BigSegmentsBuilder(store);
+        if (in.bigSegments->userCacheSize) {
+            big_segments.ContextCacheSize(*in.bigSegments->userCacheSize);
+        }
+        if (in.bigSegments->userCacheTimeMs) {
+            big_segments.ContextCacheTime(
+                std::chrono::milliseconds(*in.bigSegments->userCacheTimeMs));
+        }
+        if (in.bigSegments->statusPollIntervalMs) {
+            big_segments.StatusPollInterval(std::chrono::milliseconds(
+                *in.bigSegments->statusPollIntervalMs));
+        }
+        if (in.bigSegments->staleAfterMs) {
+            big_segments.StaleAfter(
+                std::chrono::milliseconds(*in.bigSegments->staleAfterMs));
+        }
+        config_builder.BigSegments(std::move(big_segments));
+    }
+
     auto config = config_builder.Build();
     if (!config) {
         LD_LOG(logger_, LogLevel::kWarn)
diff --git a/contract-tests/server-contract-tests/src/main.cpp b/contract-tests/server-contract-tests/src/main.cpp
index d81d12081..21ba09cf0 100644
--- a/contract-tests/server-contract-tests/src/main.cpp
+++ b/contract-tests/server-contract-tests/src/main.cpp
@@ -52,6 +52,7 @@ int main(int argc, char* argv[]) {
         srv.add_capability("track-hooks");
         srv.add_capability("wrapper");
         srv.add_capability("instance-id");
+        srv.add_capability("big-segments");
 
         net::signal_set signals{ioc, SIGINT, SIGTERM};