diff --git a/nac3artiq/src/codegen.rs b/nac3artiq/src/codegen.rs
index e3a1ec57..83ae58d5 100644
--- a/nac3artiq/src/codegen.rs
+++ b/nac3artiq/src/codegen.rs
@@ -26,6 +26,24 @@ use std::{
     sync::Arc,
 };
 
+/// The parallelism mode within a block.
+#[derive(Copy, Clone, Eq, PartialEq)]
+enum ParallelMode {
+    /// No parallelism is currently registered for this context.
+    None,
+
+    /// Legacy (or shallow) parallelism. Default before NAC3.
+    ///
+    /// Each statement within the `with` block is treated as statements to be executed in parallel.
+    Legacy,
+
+    /// Deep parallelism. Default since NAC3.
+    ///
+    /// Each function call within the `with` block (except those within a nested `sequential` block)
+    /// are treated to be executed in parallel.
+    Deep
+}
+
 pub struct ArtiqCodeGenerator<'a> {
     name: String,
 
@@ -41,6 +59,12 @@ pub struct ArtiqCodeGenerator<'a> {
     /// Variable for tracking the end of a `with parallel` block.
     end: Option<Expr<Option<Type>>>,
     timeline: &'a (dyn TimeFns + Sync),
+
+    /// The [ParallelMode] of the current parallel context.
+    ///
+    /// The current parallel context refers to the nearest `with parallel` or `with legacy_parallel`
+    /// statement, which is used to determine when and how the timeline should be updated.
+    parallel_mode: ParallelMode,
 }
 
 impl<'a> ArtiqCodeGenerator<'a> {
@@ -57,6 +81,7 @@ impl<'a> ArtiqCodeGenerator<'a> {
             start: None,
             end: None,
             timeline,
+            parallel_mode: ParallelMode::None,
         }
     }
 
@@ -141,6 +166,31 @@ impl<'b> CodeGenerator for ArtiqCodeGenerator<'b> {
         }
     }
 
+    fn gen_block<'ctx, 'a, 'c, I: Iterator<Item=&'c Stmt<Option<Type>>>>(
+        &mut self,
+        ctx: &mut CodeGenContext<'ctx, 'a>,
+        stmts: I
+    ) -> Result<(), String> where Self: Sized {
+        // Legacy parallel emits timeline end-update/timeline-reset after each top-level statement
+        // in the parallel block
+        if self.parallel_mode == ParallelMode::Legacy {
+            for stmt in stmts {
+                self.gen_stmt(ctx, stmt)?;
+
+                if ctx.is_terminated() {
+                    break;
+                }
+
+                self.timeline_update_end_max(ctx, self.end.clone(), Some("end"))?;
+                self.timeline_reset_start(ctx)?;
+            }
+
+            Ok(())
+        } else {
+            gen_block(self, ctx, stmts)
+        }
+    }
+
     fn gen_call<'ctx, 'a>(
         &mut self,
         ctx: &mut CodeGenContext<'ctx, 'a>,
@@ -150,8 +200,11 @@ impl<'b> CodeGenerator for ArtiqCodeGenerator<'b> {
     ) -> Result<Option<BasicValueEnum<'ctx>>, String> {
         let result = gen_call(self, ctx, obj, fun, params)?;
 
-        self.timeline_update_end_max(ctx, self.end.clone(), Some("end"))?;
-        self.timeline_reset_start(ctx)?;
+        // Deep parallel emits timeline end-update/timeline-reset after each function call
+        if self.parallel_mode == ParallelMode::Deep {
+            self.timeline_update_end_max(ctx, self.end.clone(), Some("end"))?;
+            self.timeline_reset_start(ctx)?;
+        }
 
         Ok(result)
     }
@@ -179,9 +232,10 @@ impl<'b> CodeGenerator for ArtiqCodeGenerator<'b> {
                 // - If there is a end variable, it indicates that we are (indirectly) inside a
                 // parallel block, and we should update the max end value.
                 if let ExprKind::Name { id, ctx: name_ctx } = &item.context_expr.node {
-                    if id == &"parallel".into() {
+                    if id == &"parallel".into() || id == &"legacy_parallel".into() {
                         let old_start = self.start.take();
                         let old_end = self.end.take();
+                        let old_parallel_mode = self.parallel_mode;
 
                         let now = if let Some(old_start) = &old_start {
                             self.gen_expr(ctx, old_start)?
@@ -224,8 +278,13 @@ impl<'b> CodeGenerator for ArtiqCodeGenerator<'b> {
                         ctx.builder.build_store(end, now);
                         self.end = Some(end_expr);
                         self.name_counter += 1;
+                        self.parallel_mode = match id.to_string().as_str() {
+                            "parallel" => ParallelMode::Deep,
+                            "legacy_parallel" => ParallelMode::Legacy,
+                            _ => unreachable!(),
+                        };
 
-                        gen_block(self, ctx, body.iter())?;
+                        self.gen_block(ctx, body.iter())?;
 
                         let current = ctx.builder.get_insert_block().unwrap();
 
@@ -258,8 +317,9 @@ impl<'b> CodeGenerator for ArtiqCodeGenerator<'b> {
                         // inside a parallel block, should update the outer max now_mu
                         self.timeline_update_end_max(ctx, old_end.clone(), Some("outer.end"))?;
 
-                        self.start = old_start;
+                        self.parallel_mode = old_parallel_mode;
                         self.end = old_end;
+                        self.start = old_start;
 
                         if reset_position {
                             ctx.builder.position_at_end(current);
@@ -267,12 +327,20 @@ impl<'b> CodeGenerator for ArtiqCodeGenerator<'b> {
 
                         return Ok(());
                     } else if id == &"sequential".into() {
+                        // For deep parallel, temporarily take away start to avoid function calls in
+                        // the block from resetting the timeline.
+                        // This does not affect legacy parallel, as the timeline will be reset after
+                        // this block finishes execution.
                         let start = self.start.take();
-                        gen_block(self, ctx, body.iter())?;
+                        self.gen_block(ctx, body.iter())?;
                         self.start = start;
 
                         // Reset the timeline when we are exiting the sequential block
-                        self.timeline_reset_start(ctx)?;
+                        // Legacy parallel does not need this, since it will be reset after codegen
+                        // for this statement is completed
+                        if self.parallel_mode == ParallelMode::Deep {
+                            self.timeline_reset_start(ctx)?;
+                        }
 
                         return Ok(());
                     }
diff --git a/nac3core/src/codegen/generator.rs b/nac3core/src/codegen/generator.rs
index 431f3455..b8b2729e 100644
--- a/nac3core/src/codegen/generator.rs
+++ b/nac3core/src/codegen/generator.rs
@@ -169,6 +169,7 @@ pub trait CodeGenerator {
     }
 
     /// Generate code for a statement
+    ///
     /// Return true if the statement must early return
     fn gen_stmt<'ctx, 'a>(
         &mut self,
@@ -181,6 +182,18 @@ pub trait CodeGenerator {
         gen_stmt(self, ctx, stmt)
     }
 
+    /// Generates code for a block statement.
+    fn gen_block<'ctx, 'a, 'b, I: Iterator<Item = &'b Stmt<Option<Type>>>>(
+        &mut self,
+        ctx: &mut CodeGenContext<'ctx, 'a>,
+        stmts: I,
+    ) -> Result<(), String>
+    where
+        Self: Sized,
+    {
+        gen_block(self, ctx, stmts)
+    }
+
     /// See [bool_to_i1].
     fn bool_to_i1<'ctx, 'a>(
         &self,
diff --git a/nac3core/src/codegen/mod.rs b/nac3core/src/codegen/mod.rs
index ddce7bcf..ae12b347 100644
--- a/nac3core/src/codegen/mod.rs
+++ b/nac3core/src/codegen/mod.rs
@@ -1,5 +1,4 @@
 use crate::{
-    codegen::stmt::gen_block,
     symbol_resolver::{StaticValue, SymbolResolver},
     toplevel::{TopLevelContext, TopLevelDef},
     typecheck::{
@@ -859,7 +858,7 @@ pub fn gen_func<'ctx, G: CodeGenerator>(
 ) -> Result<(Builder<'ctx>, Module<'ctx>, FunctionValue<'ctx>), (Builder<'ctx>, String)> {
     let body = task.body.clone();
     gen_func_impl(context, generator, registry, builder, module, task, |generator, ctx| {
-        gen_block(generator, ctx, body.iter())
+        generator.gen_block(ctx, body.iter())
     })
 }
 
diff --git a/nac3core/src/codegen/stmt.rs b/nac3core/src/codegen/stmt.rs
index 03edd1cc..65b3dbbc 100644
--- a/nac3core/src/codegen/stmt.rs
+++ b/nac3core/src/codegen/stmt.rs
@@ -322,7 +322,7 @@ pub fn gen_for<'ctx, 'a, G: CodeGenerator>(
 
             ctx.builder.position_at_end(body_bb);
             ctx.builder.build_store(target_i, ctx.builder.build_load(i, "").into_int_value());
-            gen_block(generator, ctx, body.iter())?;
+            generator.gen_block(ctx, body.iter())?;
         } else {
             let index_addr = generator.gen_var_alloc(ctx, size_t.into(), Some("for.index.addr"))?;
             ctx.builder.build_store(index_addr, size_t.const_zero());
@@ -353,7 +353,7 @@ pub fn gen_for<'ctx, 'a, G: CodeGenerator>(
             let index = ctx.builder.build_load(index_addr, "for.index").into_int_value();
             let val = ctx.build_gep_and_load(arr_ptr, &[index], Some("val"));
             generator.gen_assign(ctx, target, val.into())?;
-            gen_block(generator, ctx, body.iter())?;
+            generator.gen_block(ctx, body.iter())?;
         }
 
         for (k, (_, _, counter)) in var_assignment.iter() {
@@ -369,7 +369,7 @@ pub fn gen_for<'ctx, 'a, G: CodeGenerator>(
 
         if !orelse.is_empty() {
             ctx.builder.position_at_end(orelse_bb);
-            gen_block(generator, ctx, orelse.iter())?;
+            generator.gen_block(ctx, orelse.iter())?;
             if !ctx.is_terminated() {
                 ctx.builder.build_unconditional_branch(cont_bb);
             }
@@ -423,7 +423,7 @@ pub fn gen_while<'ctx, 'a, G: CodeGenerator>(
             unreachable!()
         };
         ctx.builder.position_at_end(body_bb);
-        gen_block(generator, ctx, body.iter())?;
+        generator.gen_block(ctx, body.iter())?;
         for (k, (_, _, counter)) in var_assignment.iter() {
             let (_, static_val, counter2) = ctx.var_assignment.get_mut(k).unwrap();
             if counter != counter2 {
@@ -435,7 +435,7 @@ pub fn gen_while<'ctx, 'a, G: CodeGenerator>(
         }
         if !orelse.is_empty() {
             ctx.builder.position_at_end(orelse_bb);
-            gen_block(generator, ctx, orelse.iter())?;
+            generator.gen_block(ctx, orelse.iter())?;
             if !ctx.is_terminated() {
                 ctx.builder.build_unconditional_branch(cont_bb);
             }
@@ -487,7 +487,7 @@ pub fn gen_if<'ctx, 'a, G: CodeGenerator>(
             unreachable!()
         };
         ctx.builder.position_at_end(body_bb);
-        gen_block(generator, ctx, body.iter())?;
+        generator.gen_block(ctx, body.iter())?;
         for (k, (_, _, counter)) in var_assignment.iter() {
             let (_, static_val, counter2) = ctx.var_assignment.get_mut(k).unwrap();
             if counter != counter2 {
@@ -503,7 +503,7 @@ pub fn gen_if<'ctx, 'a, G: CodeGenerator>(
         }
         if !orelse.is_empty() {
             ctx.builder.position_at_end(orelse_bb);
-            gen_block(generator, ctx, orelse.iter())?;
+            generator.gen_block(ctx, orelse.iter())?;
             if !ctx.is_terminated() {
                 if cont_bb.is_none() {
                     cont_bb = Some(ctx.ctx.append_basic_block(current, "cont"));
@@ -792,9 +792,9 @@ pub fn gen_try<'ctx, 'a, G: CodeGenerator>(
         }
         let old_clauses = ctx.outer_catch_clauses.replace((all_clauses, dispatcher, exn));
         let old_unwind = ctx.unwind_target.replace(landingpad);
-        gen_block(generator, ctx, body.iter())?;
+        generator.gen_block(ctx, body.iter())?;
         if ctx.builder.get_insert_block().unwrap().get_terminator().is_none() {
-            gen_block(generator, ctx, orelse.iter())?;
+            generator.gen_block(ctx, orelse.iter())?;
         }
         let body = ctx.builder.get_insert_block().unwrap();
         // reset old_clauses and old_unwind
@@ -896,7 +896,7 @@ pub fn gen_try<'ctx, 'a, G: CodeGenerator>(
                 ctx.var_assignment.insert(*name, (exn_store, None, 0));
                 ctx.builder.build_store(exn_store, exn.as_basic_value());
             }
-            gen_block(generator, ctx, body.iter())?;
+            generator.gen_block(ctx, body.iter())?;
             let current = ctx.builder.get_insert_block().unwrap();
             // only need to call end catch if not terminated
             // otherwise, we already handled in return/break/continue/raise
@@ -979,7 +979,7 @@ pub fn gen_try<'ctx, 'a, G: CodeGenerator>(
             // exception path
             let cleanup = cleanup.unwrap();
             ctx.builder.position_at_end(cleanup);
-            gen_block(generator, ctx, finalbody.iter())?;
+            generator.gen_block(ctx, finalbody.iter())?;
             if !ctx.is_terminated() {
                 ctx.build_call_or_invoke(resume, &[], "resume");
                 ctx.builder.build_unreachable();
@@ -991,7 +991,7 @@ pub fn gen_try<'ctx, 'a, G: CodeGenerator>(
             final_targets.push(tail);
             let finalizer = ctx.ctx.append_basic_block(current_fun, "try.finally");
             ctx.builder.position_at_end(finalizer);
-            gen_block(generator, ctx, finalbody.iter())?;
+            generator.gen_block(ctx, finalbody.iter())?;
             if !ctx.is_terminated() {
                 let dest = ctx.builder.build_load(final_state, "final_dest");
                 ctx.builder.build_indirect_branch(dest, &final_targets);