diff --git a/src/clientget.cpp b/src/clientget.cpp
index c1df8a1..10aebf4 100644
--- a/src/clientget.cpp
+++ b/src/clientget.cpp
@@ -111,6 +111,7 @@ struct GPROp : public OperationBase
 {
     std::function<Value(Value&&)> builder;
     std::function<void(Result&&)> done;
+    std::function<void (const Value&)> onInit;
     Value pvRequest;
     Value rpcarg;
     Result result;
@@ -135,10 +136,11 @@ struct GPROp : public OperationBase
         _cancel(true);
     }
 
-    void setDone(decltype (done)&& cb)
+    void setDone(decltype (done)&& donecb, decltype (onInit)&& initcb)
     {
-        if(cb) {
-            done = std::move(cb);
+        onInit = std::move(initcb);
+        if(donecb) {
+            done = std::move(donecb);
         } else {
             auto waiter = this->waiter = std::make_shared<ResultWaiter>();
             done = [waiter](Result&& result) {
@@ -166,10 +168,12 @@ struct GPROp : public OperationBase
     {
         auto context = chan->context;
         decltype (done) junk;
+        decltype (onInit) junkI;
         bool ret;
-        context->tcp_loop.call([this, &junk, &ret](){
+        context->tcp_loop.call([this, &junk, &junkI, &ret](){
             ret = _cancel(false);
             junk = std::move(done);
+            junkI = std::move(onInit);
             // leave opByIOID for GC
         });
         return ret;
@@ -369,6 +373,14 @@ void Connection::handle_GPR(pva_app_msg_t cmd)
 
     } else if(gpr->state==GPROp::Creating) {
 
+        try {
+            if(gpr->onInit)
+                gpr->onInit(data);
+        } catch(std::exception& e) {
+            gpr->result = Result(std::current_exception());
+            gpr->state = GPROp::Done;
+        }
+
         if(cmd==CMD_PUT && gpr->getOput) {
             gpr->state = GPROp::GetOPut;
 
@@ -493,7 +505,7 @@ std::shared_ptr<Operation> GetBuilder::_exec_get()
         auto chan = Channel::build(ctx->shared_from_this(), _name);
 
         auto op = std::make_shared<GPROp>(Operation::Get, chan);
-        op->setDone(std::move(_result));
+        op->setDone(std::move(_result), std::move(_onInit));
         op->pvRequest = _buildReq();
 
         chan->pending.push_back(op);
@@ -520,7 +532,7 @@ std::shared_ptr<Operation> PutBuilder::exec()
         auto chan = Channel::build(ctx->shared_from_this(), _name);
 
         auto op = std::make_shared<GPROp>(Operation::Put, chan);
-        op->setDone(std::move(_result));
+        op->setDone(std::move(_result), std::move(_onInit));
 
         if(_builder) {
             op->builder = std::move(_builder);
@@ -561,7 +573,7 @@ std::shared_ptr<Operation> RPCBuilder::exec()
         auto chan = Channel::build(ctx->shared_from_this(), _name);
 
         auto op = std::make_shared<GPROp>(Operation::RPC, chan);
-        op->setDone(std::move(_result));
+        op->setDone(std::move(_result), std::move(_onInit));
         if(_argument) {
             op->rpcarg = std::move(_argument);
         } else if(_args) {
diff --git a/src/clientmon.cpp b/src/clientmon.cpp
index 1cd7075..5f0cf67 100644
--- a/src/clientmon.cpp
+++ b/src/clientmon.cpp
@@ -39,6 +39,7 @@ struct SubscriptionImpl : public OperationBase, public Subscription
     evevent ackTick;
 
     // const after exec()
+    std::function<void (const Value&)> onInit;
     std::function<void(Subscription&)> event;
     Value pvRequest;
     bool pipeline = false;
@@ -447,6 +448,9 @@ void Connection::handle_MONITOR()
                         peerName.c_str(),
                         mon->chan->name.c_str());
 
+        if(mon->onInit)
+            mon->onInit(info->prototype);
+
         mon->state = SubscriptionImpl::Idle;
 
         if(mon->autostart)
@@ -547,6 +551,7 @@ std::shared_ptr<Subscription> MonitorBuilder::exec()
 
         auto op = std::make_shared<SubscriptionImpl>(Operation::Monitor, chan);
         op->event = std::move(_event);
+        op->onInit = std::move(_onInit);
         op->pvRequest = _buildReq();
         op->maskConn = _maskConn;
         op->maskDiscon = _maskDisconn;
diff --git a/src/pvxs/client.h b/src/pvxs/client.h
index 2f98912..1bdc36e 100644
--- a/src/pvxs/client.h
+++ b/src/pvxs/client.h
@@ -496,6 +496,7 @@ protected:
 template<typename SubBuilder, typename Base>
 class CommonBuilder : public Base {
 protected:
+    std::function<void (const Value&)> _onInit;
     CommonBuilder() = default;
     constexpr CommonBuilder(const std::shared_ptr<Context::Pvt>& ctx, const std::string& name) : Base(ctx, name) {}
     inline SubBuilder& _sb() { return static_cast<SubBuilder&>(*this); }
@@ -537,6 +538,11 @@ public:
 
     SubBuilder& priority(int p) { this->_prio = p; return _sb(); }
     SubBuilder& server(const std::string& s) { this->_server = s; return _sb(); }
+
+    // Expert API
+    // called during operation INIT phase for Get/Put/Monitor when remote type
+    // description is available.
+    SubBuilder& onInit(std::function<void (const Value&)>&& cb) { this->_onInit = std::move(cb); return _sb(); }
 };
 
 } // namespace detail
diff --git a/test/testget.cpp b/test/testget.cpp
index 02e3acc..907644a 100644
--- a/test/testget.cpp
+++ b/test/testget.cpp
@@ -101,14 +101,21 @@ struct Tester {
 
         mbox.open(initial);
         serv.start();
+        std::atomic<bool> hadInit{false};
 
-        auto op = cli.get("mailbox").exec();
+        auto op = cli.get("mailbox")
+                .onInit([&hadInit](const Value& prototype) {
+                    testShow()<<"onInit() << "<<prototype;
+                    hadInit.store(prototype["value"].valid());
+                })
+                .exec();
 
         cli.hurryUp();
 
         auto result = op->wait(5.0);
 
         testEq(result["value"].as<int32_t>(), 42);
+        testTrue(hadInit.load());
     }
 
     void testWait()
@@ -302,7 +309,7 @@ void testError(bool phase)
 
 MAIN(testget)
 {
-    testPlan(23);
+    testPlan(24);
     testSetup();
     logger_config_env();
     Tester().testConnector();