After talking about Hemi for so long, the point that excites me the most is that hVM (Hemi Virtual Machine) can "natively read" the state of Bitcoin L1. This is technically so sexy that it opens the door to native BTCFi. But after the excitement, my research over the past few days has started to shift towards calmness and scrutiny: how exactly is this "reading" achieved? How do the nodes of the Hemi protocol "see" the L1 state? Is the process of this "seeing" itself reliable? My conclusion is that this "built-in L1 observer" of hVM is both Hemi's greatest innovation and possibly its most hidden "consensus bomb."
We must first strip away the marketing packaging of the term 'native reading' and delve into its engineering implementation. This functionality is not magic; it is backed by a complex set of mechanisms with trade-offs.
First, Hemi nodes (especially PoS validator nodes) must run one (or more) L1 nodes (or light clients) themselves. When Hemi claims that hVM can read the Bitcoin state, it does not mean that the Solidity contract 'floats' onto the Bitcoin chain to execute. What it really means is that each Hemi validator node, in addition to running the PoS consensus client for the Hemi chain, must also run a Bitcoin full node (or a highly trusted light client) in the same 'chassis'.
This architectural choice immediately brings several significant technical and economic challenges:
1. The 'implicit costs' of node operators
This greatly raises the entry threshold and operational costs for Hemi validators. A typical PoS validator only needs to maintain the stable operation of its own chain. However, Hemi validators must now simultaneously maintain the stable synchronization and data integrity of Hemi nodes, Bitcoin nodes (and possibly Ethereum nodes in the future). The data size of a Bitcoin full node is several hundred GB and is continuously growing. This poses higher requirements for bandwidth, storage, and CPU. If hVM also needs to parse Ordinals, it will have to run an Ordinals indexer! Does this lead to 'centralization' of the Hemi network's validators? Only those with ample resources and strong technical capabilities, the 'professional big players', can manage this, while small retail nodes cannot bear such 'three-in-one' operational pressures?
2. The consensus dilemma of 'L1 state'
This is the most critical issue. Hemi is a PoS chain, and it internally needs to reach consensus on 'L2 transactions'. Now, it has an additional task: all of Hemi's validators must reach consensus on 'what the state of L1 is'.
Let's imagine a scenario: Bitcoin L1 experiences a reorganization of 3 blocks. There are 100 validators in the Hemi network. Due to network latency or differences in P2P propagation, 70 validators may have 'seen' chain A (the chain before reorganization), while 30 validators 'saw' chain B (the chain after reorganization).
At this point, the consensus of the Hemi chain encounters problems. Those 70 validators believe 'User A's BTC deposit has been confirmed', while the 30 validators believe 'this deposit does not exist'. How should the L2 state of the Hemi chain proceed? This is an example of a failure of 'L1 observation consensus'.
How do traditional cross-chain bridges solve this problem? They use 'external oracles'. For example, Chainlink or a multi-signature witness alliance. This alliance (for instance, 10 nodes) observes L1 and then 'votes' to determine the real state of L1, feeding this 'post-consensus' result to the L2 contract.
Hemi's hVM essentially internalizes the work of this 'external oracle' as part of the 'core consensus' of the Hemi chain. It is equivalent to saying: 'My 100 PoS validators also serve as this oracle alliance.'
3. The tricky trade-offs of 'finality'
This 'L1 Observation Consensus' must also deal with two completely different types of 'finality'. If hVM needs to read Bitcoin (PoW) and Ethereum (PoS):
Reading Ethereum (PoS) is more manageable. Ethereum PoS has a clear 'Finalized' state (about 15 minutes). Hemi validators can simply set a rule: 'only read and respond to Ethereum Finalized block data'. This is safe, but the cost is latency.
Reading Bitcoin (PoW) is already a headache. Bitcoin never has absolute 'finality', only 'probabilistic finality'. The industry standard is to wait for 6 blocks (~1 hour), considering the probability of rollback to be negligible.
The Hemi protocol must hard-code a BTC_CONFIRMATION_DEPTH in the code (for example, 6 or 10). When the smart contract on Hemi calls to 'read the BTC state' in hVM, it reads not the latest block of L1, but the 'safe state' that has been 'confirmed' by Hemi consensus N blocks prior.
This N value becomes Hemi's 'Achilles' heel'. If N is too small (for example, 3), the speed is fast, but hVM runs the risk of being 'slapped in the face' by L1 reorganization. If N is too large (for example, 10), it's secure, but users depositing BTC into Hemi must wait 100 minutes, resulting in a poor experience.
The 'L1 state reading' of hVM is not a simple 'API call'; it is an additional layer of 'L1 state observation consensus' that overlays the PoS consensus of the Hemi chain.
It has transformed the 'oracle', the most prone to security issues, from 'external dependency' to 'internal core'. Is this safer? It's hard to say. It merely shifts the risk of 'trusting third-party oracles' to a new risk of 'trusting the Hemi validator group to correctly and consistently observe L1'.
This design is highly ambitious, but its internal complexity and potential attack vectors (such as coordinated attacks on Hemi's 'L1 observation consensus' through L1 reorganization + L2 network partition) are unprecedented. In Hemi's code audit report, the module for 'L1 state synchronization and reorganization handling' in hVM is definitely the first place I would look.
