Overview
The Radix Engine is the execution environment that runs all Scrypto smart contracts on Radix. Unlike the EVM (which is a general-purpose virtual machine), the Radix Engine is purpose-built for DeFi with asset-oriented programming enforced at the system level.
System-Level Enforcement
The Radix Engine enforces asset conservation, access rules, and resource behaviors (mint, burn, freeze) at the engine level – not in application code. This means an entire class of bugs (reentrancy, overflow, approval exploits) is structurally impossible.
Deterministic Execution
Every transaction produces the same result regardless of execution timing or node. Combined with transaction manifests, users can predict exactly what a transaction will do before signing.
The Radix Engine and Xi'an
The Radix Engine is the execution environment of Babylon mainnet, and everything above describes what runs there today. Its role in the sharded successor network is changing.
On 1 August 2026 the lead developer of the Xi'an production candidate confirmed that a purpose-built virtual machine is underway to replace the Radix Engine in Xi'an, having assessed the engine as "not in the ballpark" for sharded operation. The candidate integrates the real engine today, so this is a stated direction rather than a completed change.
The technical objection is narrow and specific. Cross-shard atomic commitment requires every transaction to declare in advance exactly which state it will read and write, because that declaration fixes which shards participate and lets conflicts be analysed before anything executes. The Radix Engine's state access is, on the developer's assessment, "too loose" to resolve those dependencies deterministically ahead of execution for a Turing-complete contract language – which leaves only unattractive routes to transaction preview, such as an ingress node holding state from every shard, or discovering each dependency part-way through execution.
For developers, the expected migration cost was given on 2 August 2026 as "best case scenario - contracts will just need a recompile. worst case scenario - there'll be some automatic transpiler devs can use to upgrade source code". How much the new VM borrows from the Radix Engine has not been stated beyond an April 2026 remark that it "might borrow some ideas from RE".