diff --git a/host/src/lib.rs b/host/src/lib.rs
index a4df64dc..e3d14b37 100644
--- a/host/src/lib.rs
+++ b/host/src/lib.rs
@@ -152,6 +152,7 @@ pub struct ProverState {
 pub enum Message {
     Cancel(TaskDescriptor),
     Task(ProofRequest),
+    TaskComplete(ProofRequest),
 }
 
 impl From<&ProofRequest> for Message {
@@ -192,9 +193,9 @@ impl ProverState {
 
         let opts_clone = opts.clone();
         let chain_specs_clone = chain_specs.clone();
-
+        let sender = task_channel.clone();
         tokio::spawn(async move {
-            ProofActor::new(receiver, opts_clone, chain_specs_clone)
+            ProofActor::new(sender, receiver, opts_clone, chain_specs_clone)
                 .run()
                 .await;
         });
diff --git a/host/src/proof.rs b/host/src/proof.rs
index 31a56e72..e48cb07b 100644
--- a/host/src/proof.rs
+++ b/host/src/proof.rs
@@ -1,4 +1,7 @@
-use std::{collections::HashMap, sync::Arc};
+use std::{
+    collections::{HashMap, VecDeque},
+    sync::Arc,
+};
 
 use raiko_core::{
     interfaces::{ProofRequest, RaikoError},
@@ -13,10 +16,13 @@ use raiko_lib::{
 use raiko_tasks::{get_task_manager, TaskDescriptor, TaskManager, TaskManagerWrapper, TaskStatus};
 use tokio::{
     select,
-    sync::{mpsc::Receiver, Mutex, OwnedSemaphorePermit, Semaphore},
+    sync::{
+        mpsc::{Receiver, Sender},
+        Mutex,
+    },
 };
 use tokio_util::sync::CancellationToken;
-use tracing::{error, info, warn};
+use tracing::{debug, error, info, warn};
 
 use crate::{
     cache,
@@ -32,26 +38,36 @@ use crate::{
 pub struct ProofActor {
     opts: Opts,
     chain_specs: SupportedChainSpecs,
-    tasks: Arc<Mutex<HashMap<TaskDescriptor, CancellationToken>>>,
+    running_tasks: Arc<Mutex<HashMap<TaskDescriptor, CancellationToken>>>,
+    pending_tasks: Arc<Mutex<VecDeque<ProofRequest>>>,
     receiver: Receiver<Message>,
+    sender: Sender<Message>,
 }
 
 impl ProofActor {
-    pub fn new(receiver: Receiver<Message>, opts: Opts, chain_specs: SupportedChainSpecs) -> Self {
-        let tasks = Arc::new(Mutex::new(
+    pub fn new(
+        sender: Sender<Message>,
+        receiver: Receiver<Message>,
+        opts: Opts,
+        chain_specs: SupportedChainSpecs,
+    ) -> Self {
+        let running_tasks = Arc::new(Mutex::new(
             HashMap::<TaskDescriptor, CancellationToken>::new(),
         ));
+        let pending_tasks = Arc::new(Mutex::new(VecDeque::<ProofRequest>::new()));
 
         Self {
-            tasks,
             opts,
             chain_specs,
+            running_tasks,
+            pending_tasks,
             receiver,
+            sender,
         }
     }
 
     pub async fn cancel_task(&mut self, key: TaskDescriptor) -> HostResult<()> {
-        let tasks_map = self.tasks.lock().await;
+        let tasks_map = self.running_tasks.lock().await;
         let Some(task) = tasks_map.get(&key) else {
             warn!("No task with those keys to cancel");
             return Ok(());
@@ -76,7 +92,7 @@ impl ProofActor {
         Ok(())
     }
 
-    pub async fn run_task(&mut self, proof_request: ProofRequest, _permit: OwnedSemaphorePermit) {
+    pub async fn run_task(&mut self, proof_request: ProofRequest) {
         let cancel_token = CancellationToken::new();
 
         let Ok((chain_id, blockhash)) = get_task_data(
@@ -97,10 +113,11 @@ impl ProofActor {
             proof_request.prover.clone().to_string(),
         ));
 
-        let mut tasks = self.tasks.lock().await;
+        let mut tasks = self.running_tasks.lock().await;
         tasks.insert(key.clone(), cancel_token.clone());
+        let sender = self.sender.clone();
 
-        let tasks = self.tasks.clone();
+        let tasks = self.running_tasks.clone();
         let opts = self.opts.clone();
         let chain_specs = self.chain_specs.clone();
 
@@ -109,7 +126,7 @@ impl ProofActor {
                 _ = cancel_token.cancelled() => {
                     info!("Task cancelled");
                 }
-                result = Self::handle_message(proof_request, key.clone(), &opts, &chain_specs) => {
+                result = Self::handle_message(proof_request.clone(), key.clone(), &opts, &chain_specs) => {
                     match result {
                         Ok(status) => {
                             info!("Host handling message: {status:?}");
@@ -122,25 +139,56 @@ impl ProofActor {
             }
             let mut tasks = tasks.lock().await;
             tasks.remove(&key);
+            // notify complete task to let next pending task run
+            sender
+                .send(Message::TaskComplete(proof_request))
+                .await
+                .expect("Couldn't send message");
         });
     }
 
     pub async fn run(&mut self) {
-        let semaphore = Arc::new(Semaphore::new(self.opts.concurrency_limit));
-
+        // recv() is protected by outside mpsc, no lock needed here
         while let Some(message) = self.receiver.recv().await {
             match message {
                 Message::Cancel(key) => {
+                    debug!("Message::Cancel task: {:?}", key);
                     if let Err(error) = self.cancel_task(key).await {
                         error!("Failed to cancel task: {error}")
                     }
                 }
                 Message::Task(proof_request) => {
-                    let permit = Arc::clone(&semaphore)
-                        .acquire_owned()
-                        .await
-                        .expect("Couldn't acquire permit");
-                    self.run_task(proof_request, permit).await;
+                    debug!("Message::Task proof_request: {:?}", proof_request);
+                    let running_task_count = self.running_tasks.lock().await.len();
+                    if running_task_count < self.opts.concurrency_limit {
+                        info!("Running task {:?}", proof_request);
+                        self.run_task(proof_request).await;
+                    } else {
+                        info!(
+                            "Task concurrency limit reached, current running {:?}, pending: {:?}",
+                            running_task_count,
+                            self.pending_tasks.lock().await.len()
+                        );
+                        let mut pending_tasks = self.pending_tasks.lock().await;
+                        pending_tasks.push_back(proof_request);
+                    }
+                }
+                Message::TaskComplete(req) => {
+                    // pop up pending task if any task complete
+                    debug!("Message::TaskComplete: {:?}", req);
+                    info!(
+                        "task completed, current running {:?}, pending: {:?}",
+                        self.running_tasks.lock().await.len(),
+                        self.pending_tasks.lock().await.len()
+                    );
+                    let mut pending_tasks = self.pending_tasks.lock().await;
+                    if let Some(proof_request) = pending_tasks.pop_front() {
+                        info!("Pop out pending task {:?}", proof_request);
+                        self.sender
+                            .send(Message::Task(proof_request))
+                            .await
+                            .expect("Couldn't send message");
+                    }
                 }
             }
         }
@@ -190,7 +238,7 @@ pub async fn handle_proof(
     store: Option<&mut TaskManagerWrapper>,
 ) -> HostResult<Proof> {
     info!(
-        "# Generating proof for block {} on {}",
+        "Generating proof for block {} on {}",
         proof_request.block_number, proof_request.network
     );