diff --git a/recursion/compiler/src/circuit/mod.rs b/recursion/compiler/src/circuit/mod.rs
index 6098320b30..eb1a350d86 100644
--- a/recursion/compiler/src/circuit/mod.rs
+++ b/recursion/compiler/src/circuit/mod.rs
@@ -7,7 +7,7 @@ pub use compiler::*;
 #[cfg(test)]
 mod tests {
     use p3_baby_bear::DiffusionMatrixBabyBear;
-    use p3_field::AbstractExtensionField;
+    use p3_field::{AbstractExtensionField, AbstractField};
     use rand::{rngs::StdRng, Rng, SeedableRng};
     use sp1_core::{
         stark::{Chip, StarkGenericConfig, StarkMachine, PROOF_MAX_NUM_PVS},
@@ -23,10 +23,14 @@ mod tests {
             poseidon2_wide::Poseidon2WideChip,
         },
         machine::RecursionAir,
-        Runtime,
+        Runtime, RuntimeError,
     };
 
-    use crate::{asm::AsmBuilder, circuit::AsmCompiler, ir::*};
+    use crate::{
+        asm::AsmBuilder,
+        circuit::{AsmCompiler, CircuitV2Builder},
+        ir::*,
+    };
 
     const DEGREE: usize = 3;
 
@@ -119,4 +123,100 @@ mod tests {
 
         tracing::info!("num shard proofs: {}", result.shard_proofs.len());
     }
+
+    #[test]
+    fn test_io() {
+        let mut builder = AsmBuilder::<F, EF>::default();
+
+        let felts = builder.hint_felts_v2(3);
+        assert_eq!(felts.len(), 3);
+        let sum: Felt<_> = builder.eval(felts[0] + felts[1]);
+        builder.assert_felt_eq(sum, felts[2]);
+
+        let exts = builder.hint_exts_v2(3);
+        assert_eq!(exts.len(), 3);
+        let sum: Ext<_, _> = builder.eval(exts[0] + exts[1]);
+        builder.assert_ext_ne(sum, exts[2]);
+
+        let x = builder.hint_ext_v2();
+        builder.assert_ext_eq(x, exts[0] + felts[0]);
+
+        let y = builder.hint_felt_v2();
+        let zero: Felt<_> = builder.constant(F::zero());
+        builder.assert_felt_eq(y, zero);
+
+        let operations = builder.operations;
+        let mut compiler = AsmCompiler::default();
+        let program = compiler.compile(operations);
+        let mut runtime = Runtime::<F, EF, DiffusionMatrixBabyBear>::new(&program, SC::new().perm);
+        runtime.witness_stream = [
+            vec![F::one().into(), F::one().into(), F::two().into()],
+            vec![F::zero().into(), F::one().into(), F::two().into()],
+            vec![F::one().into()],
+            vec![F::zero().into()],
+        ]
+        .into();
+        runtime.run().unwrap();
+
+        let machine = A::machine(SC::new());
+
+        let (pk, vk) = machine.setup(&program);
+        let result =
+            run_test_machine(vec![runtime.record], machine, pk, vk.clone()).expect("should verify");
+
+        tracing::info!("num shard proofs: {}", result.shard_proofs.len());
+    }
+
+    #[test]
+    fn test_empty_witness_stream() {
+        let mut builder = AsmBuilder::<F, EF>::default();
+
+        let felts = builder.hint_felts_v2(3);
+        assert_eq!(felts.len(), 3);
+        let sum: Felt<_> = builder.eval(felts[0] + felts[1]);
+        builder.assert_felt_eq(sum, felts[2]);
+
+        let exts = builder.hint_exts_v2(3);
+        assert_eq!(exts.len(), 3);
+        let sum: Ext<_, _> = builder.eval(exts[0] + exts[1]);
+        builder.assert_ext_ne(sum, exts[2]);
+
+        let operations = builder.operations;
+        let mut compiler = AsmCompiler::default();
+        let program = compiler.compile(operations);
+        let mut runtime = Runtime::<F, EF, DiffusionMatrixBabyBear>::new(&program, SC::new().perm);
+        runtime.witness_stream = [vec![F::one().into(), F::one().into(), F::two().into()]].into();
+
+        match runtime.run() {
+            Err(RuntimeError::EmptyWitnessStream) => (),
+            Ok(_) => panic!("should not succeed"),
+            Err(x) => panic!("should not yield error variant: {}", x),
+        }
+    }
+
+    #[test]
+    fn test_mismatched_witness_size() {
+        const MEM_VEC_LEN: usize = 3;
+        const WITNESS_LEN: usize = 5;
+
+        let mut builder = AsmBuilder::<F, EF>::default();
+
+        let felts = builder.hint_felts_v2(MEM_VEC_LEN);
+        assert_eq!(felts.len(), MEM_VEC_LEN);
+
+        let operations = builder.operations;
+        let mut compiler = AsmCompiler::default();
+        let program = compiler.compile(operations);
+        let mut runtime = Runtime::<F, EF, DiffusionMatrixBabyBear>::new(&program, SC::new().perm);
+        runtime.witness_stream = [vec![F::zero().into(); WITNESS_LEN]].into();
+
+        match runtime.run() {
+            Err(RuntimeError::WitnessLenMismatch {
+                mem_vec_len: MEM_VEC_LEN,
+                witness_len: WITNESS_LEN,
+            }) => (),
+            Ok(_) => panic!("should not succeed"),
+            Err(x) => panic!("should not yield error variant: {}", x),
+        }
+    }
 }
diff --git a/recursion/core-v2/src/runtime/mod.rs b/recursion/core-v2/src/runtime/mod.rs
index cd2ffc6be3..5dca4059a7 100644
--- a/recursion/core-v2/src/runtime/mod.rs
+++ b/recursion/core-v2/src/runtime/mod.rs
@@ -158,8 +158,8 @@ pub enum RuntimeError<F: Debug, EF: Debug> {
     },
     #[error("failed to print to `debug_stdout`: {0}")]
     DebugPrint(#[from] std::io::Error),
-    #[error("attempted to read vec of {0:?} from empty witness stream")]
-    EmptyWitnessStream(FieldEltType),
+    #[error("attempted to read from empty witness stream")]
+    EmptyWitnessStream,
     #[error("attempted to write to memory vec of len {mem_vec_len} witness of size {witness_len}")]
     WitnessLenMismatch {
         mem_vec_len: usize,
@@ -572,7 +572,7 @@ where
                     let witness = self
                         .witness_stream
                         .pop_front()
-                        .ok_or(RuntimeError::EmptyWitnessStream(FieldEltType::Base))?;
+                        .ok_or(RuntimeError::EmptyWitnessStream)?;
                     // Check the lengths are the same.
                     if output_addrs_mults.len() != witness.len() {
                         return Err(RuntimeError::WitnessLenMismatch {