diff --git a/crates/blockifier/src/fee/eth_gas_constants.rs b/crates/blockifier/src/fee/eth_gas_constants.rs
index 6c337ea2459..e01eb731322 100644
--- a/crates/blockifier/src/fee/eth_gas_constants.rs
+++ b/crates/blockifier/src/fee/eth_gas_constants.rs
@@ -1,6 +1,7 @@
 // Calldata.
 pub const GAS_PER_MEMORY_ZERO_BYTE: usize = 4;
 pub const GAS_PER_MEMORY_BYTE: usize = 16;
+// TODO(AvivG): use starknet_api::core::WORD_WIDTH instead.
 pub const WORD_WIDTH: usize = 32;
 pub const GAS_PER_MEMORY_WORD: usize = GAS_PER_MEMORY_BYTE * WORD_WIDTH;
 
diff --git a/crates/starknet_api/src/contract_class.rs b/crates/starknet_api/src/contract_class.rs
index e633e3e4ae7..72f4bde1616 100644
--- a/crates/starknet_api/src/contract_class.rs
+++ b/crates/starknet_api/src/contract_class.rs
@@ -1,8 +1,9 @@
 use cairo_lang_starknet_classes::casm_contract_class::CasmContractClass;
 use serde::{Deserialize, Serialize};
 
-use crate::core::CompiledClassHash;
+use crate::core::{CompiledClassHash, WORD_WIDTH};
 use crate::deprecated_contract_class::ContractClass as DeprecatedContractClass;
+use crate::StarknetApiError;
 
 #[derive(
     Debug, Default, Clone, Copy, Eq, PartialEq, Hash, Deserialize, Serialize, PartialOrd, Ord,
@@ -41,9 +42,58 @@ impl ContractClass {
 /// All relevant information about a declared contract class, including the compiled contract class
 /// and other parameters derived from the original declare transaction required for billing.
 #[derive(Clone, Debug, Deserialize, Eq, PartialEq, Serialize)]
+// TODO(Ayelet,10/02/2024): Change to bytes.
 pub struct ClassInfo {
     // TODO(Noa): Consider using Arc.
     pub contract_class: ContractClass,
     pub sierra_program_length: usize,
     pub abi_length: usize,
 }
+
+impl ClassInfo {
+    pub fn bytecode_length(&self) -> usize {
+        match &self.contract_class {
+            ContractClass::V0(contract_class) => contract_class.bytecode_length(),
+            ContractClass::V1(contract_class) => contract_class.bytecode.len(),
+        }
+    }
+
+    pub fn contract_class(&self) -> ContractClass {
+        self.contract_class.clone()
+    }
+
+    pub fn sierra_program_length(&self) -> usize {
+        self.sierra_program_length
+    }
+
+    pub fn abi_length(&self) -> usize {
+        self.abi_length
+    }
+
+    pub fn code_size(&self) -> usize {
+        (self.bytecode_length() + self.sierra_program_length())
+            // We assume each felt is a word.
+            * WORD_WIDTH
+            + self.abi_length()
+    }
+
+    pub fn new(
+        contract_class: &ContractClass,
+        sierra_program_length: usize,
+        abi_length: usize,
+    ) -> Result<Self, StarknetApiError> {
+        let (contract_class_version, condition) = match contract_class {
+            ContractClass::V0(_) => (0, sierra_program_length == 0),
+            ContractClass::V1(_) => (1, sierra_program_length > 0),
+        };
+
+        if condition {
+            Ok(Self { contract_class: contract_class.clone(), sierra_program_length, abi_length })
+        } else {
+            Err(StarknetApiError::ContractClassVersionSierraProgramLengthMismatch {
+                contract_class_version,
+                sierra_program_length,
+            })
+        }
+    }
+}
diff --git a/crates/starknet_api/src/core.rs b/crates/starknet_api/src/core.rs
index 93f9dea540a..22b0f2a7d35 100644
--- a/crates/starknet_api/src/core.rs
+++ b/crates/starknet_api/src/core.rs
@@ -16,6 +16,10 @@ use crate::serde_utils::{BytesAsHex, PrefixedBytesAsHex};
 use crate::transaction::{Calldata, ContractAddressSalt};
 use crate::{impl_from_through_intermediate, StarknetApiError};
 
+// Ethereum constant.
+/// One Felt fits into 32 bytes.
+pub const WORD_WIDTH: usize = 32;
+
 /// Felt.
 pub fn ascii_as_felt(ascii_str: &str) -> Result<Felt, StarknetApiError> {
     Felt::from_hex(hex::encode(ascii_str).as_str())
diff --git a/crates/starknet_api/src/lib.rs b/crates/starknet_api/src/lib.rs
index 98f9f42edab..4ba0366232d 100644
--- a/crates/starknet_api/src/lib.rs
+++ b/crates/starknet_api/src/lib.rs
@@ -49,6 +49,14 @@ pub enum StarknetApiError {
     InvalidStarknetVersion(Vec<u8>),
     #[error("NonzeroGasPrice cannot be zero.")]
     ZeroGasPrice,
+    #[error(
+        "Sierra program length must be > 0 for Cairo1, and == 0 for Cairo0. Got: \
+         {sierra_program_length:?} for contract class version {contract_class_version:?}"
+    )]
+    ContractClassVersionSierraProgramLengthMismatch {
+        contract_class_version: u8,
+        sierra_program_length: usize,
+    },
 }
 
 pub type StarknetApiResult<T> = Result<T, StarknetApiError>;