According to analysis from the team of experts at Tan Phat Digital, in the architecture of distributed systems and decentralized ledger technology, the concept of "Finality" represents an important technical and legal milestone, marking the moment when a transaction or a set of state changes can no longer be changed, revoked or reversed. However, contrary to the popular perception of blockchain's absolute immutability, extensive technical analysis shows that Finality is essentially a function of beliefs, probabilities, and economic barriers rather than a permanent mathematical state. Understanding the conditions under which a seemingly completed transaction can be reversed is paramount for financial institutions, protocol developers, and professional users as they navigate the dramatically shifting blockchain infrastructure landscape from 2025 to 2026.
The nature of finality in decentralized ledger systems
Transaction completeness is about more than just a technical specification but also a core legal concept. In traditional finance, finality of payment is determined by legal frameworks that dictate when ownership of assets is unconditionally transferred. In blockchain, the separation between "Operational Finality" (when the system confirms transactions) and "Legal Finality" (when the law recognizes ownership) creates a risk gap, especially in probability-based systems. This risk arises from the fact that consensus protocols must solve the Byzantine Fault Tolerance (BFT) problem while still maintaining network availability.
The main types of Finality today include:
Probabilistic Finality: Based on the work accumulation mechanism (PoW). Applies mainly to Bitcoin, Monero, Litecoin. The time achieved is often slow (needs 6+ confirmation blocks) and there is a risk of reversal if a deep chain reorganization (Reorg) occurs.
Economic Finality: Based on the staking and penalty mechanism (Slashing) in Proof-of-Stake. Typically Ethereum with Gasper protocol. The average time achieved is about 12.8 minutes. Reversal is extremely difficult due to the huge economic cost required to attack.
Instant Finality: Based on the absolute majority voting mechanism (BFT Supermajority Voting). Applies to networks such as Cosmos or Solana (2026 version). The time achieved is very fast (under 1 second) and almost impossible to reverse unless there is a serious error in the source code.
Layered Finality: Uses a sequencer and State Roots. Applies to Layer 2 such as Arbitrum, Optimism. Transactions reach "soft" state instantly but take minutes to days to reach "hard" state on Layer 1.
Finality probability and risk of chain reorganization in Proof-of-Work
In systems that use the Nakamoto consensus algorithm such as Bitcoin, a transaction never achieves absolute mathematical completion. Instead, the reliability of the transaction increases over time as more new blocks are mined over the block containing that transaction.
Chain Reorganization Mechanism
Chain Reorganization (Reorg) is a natural phenomenon but carries the risk of transaction reversal. When two miners find two valid blocks at the same time, the network is temporarily split into two branches. According to the "longest chain" rule (or the chain with the most accumulated work), network nodes will automatically switch to whichever branch develops faster. When this happens, the shorter branch is discarded, and the blocks within it become "orphaned blocks".
Transactions in these discarded blocks, if not present in the winning chain, are considered to never have occurred and are sent back to the mempool. While 1 block deep Reorgs are frequent and harmless, deeper Reorgs can be a sign of network instability or a targeted attack.
See also: Can Blockchain transactions be reversed?
51% attack and typical example from Monero (August 2025)
51% attack is the worst scenario for probabilistic Finality. If an entity controls more than half of the network's computing power, they can create a private chain at a faster rate than the public chain and then publish it to overwrite the transaction history. This allows attackers to perform "double-spending" by deleting their own previously confirmed transfers.
A shocking real-world case occurred in August 2025 with the Monero network. Mining pool Qubic has redirected its capacity towards Monero mining by offering triple rewards to miners. This sudden hashrate shift allowed Qubic to carry out a chain reorganization six blocks deep, eliminating around 60 official blocks and shaking confidence in the decentralization of privacy coins. This event proves that the security of Proof-of-Work is not only based on mathematics but also depends heavily on economic incentives.
See more: 51% Attack (51% Attack) is What?
Ethereum and the Transition to Single Slot Finality (2025-2027)
Ethereum currently uses the Gasper consensus protocol. In the current model, blocks are proposed every 12 seconds, but to achieve economic completeness, the network needs approximately 12.8 minutes.
Risk over a period of 12.8 minutes
This delay creates a significant "risk window". During this time, transactions only have temporary confirmations and can be reversed if an epoch-level Reorg occurs. Furthermore, this delay allows MEV actors to perform short-term chain reorganization attacks to profit from changing the order of transactions. This is especially dangerous for large-value financial transactions or liquidation operations in DeFi.
Single Slot Finality (SSF) Roadmap and Technical Hurdles
To address this issue, Ethereum's upgrade roadmap moves towards Single Slot Finality (SSF), which is expected to be fully deployed by the end of 2026 or 2027. The goal of SSF is to lock down a block right in the slot in which it is proposed (12 seconds), completely eliminating the possibility of Reorg.
Technical solutions being researched include:
Horn Protocol and signature aggregation using ZK-SNARK:Using Zero-Knowledge Proofs technology to compress tens of thousands of signatures into a single proof, making it possible for even weak network nodes to verify the validity of the entire committee validator.
Orbit Committees:Choose moderately sized committees that still ensure extremely high economic attack costs, balancing decentralization and performance.
Model-Checking for SSF: Use mathematical checking tools to ensure there is no scenario that allows two conflicting blocks to be completed simultaneously time.
Solana Alpenglow: As speeds approach Web2 infrastructure
Solana has taken the lead in providing a near-instant trading experience, but the network still has a gap between "optimistic confirmation" and "absolute finality". The Alpenglow upgrade (2025-2026) is designed to close this gap.
Details of Solana's changes through phases:
Solana (Agave Architecture - Present):
Finality Time: Approximately 12.8 seconds.
Optimistic Confirmation: 400-800 milliseconds.
Consensus protocol: Proof-of-History + TowerBFT.
Data transfer protocol: Turbine (multi-layer).
Security model: BFT standard.
Solana (Alpenglow Architecture - Year 2026):
Time Finality time: Shortened to 100-150 milliseconds.
Consensus protocol: Votor (two-round voting mechanism helps finalize the specified block).
Data transmission protocol: Rotor (direct message transmission via one hop - one-hop).
Safety model: 20+20 system (remains secure if 20% validator attacks and 20% offline).
As a result, Solana in 2026 will deliver true finality faster than Google Search response speeds, suitable for high-frequency trading (HFT) and Web3 gaming without worrying about reverse risk.
Layered finality in the Layer 2 (L2) ecosystem
Layer 2 solutions like Arbitrum and Optimism split finality into two states main:
Soft Finality: Usually only takes 1-2 seconds. Once the transaction is sent, the Sequencer sends back a "commitment" that the transaction has been recorded. However, this state relies entirely on the Sequencer's honesty. If the Sequencer cheats before sending data to Layer 1, the transaction can be reversed.
Hard Finality: Usually takes about 12-19 minutes. Occurs when data is packaged into "blobs" and sent to Ethereum. Once the block containing this data on Ethereum is finalized, the L2 transaction becomes immutable.
In 2026, "Shared Sequencers" solutions are being developed to decentralize this Sequencer layer, minimizing the risk of reversal right from the soft confirmation stage.
Risk of reversal from software errors and human intervention
Even if the algorithm works perfect, Finality can still be broken by non-technical factors:
Manual intervention (Social Consensus): A typical example is The DAO hack in 2016, where the Ethereum community decided to Hard Fork to "turn back time". Or times when Solana goes offline, it requires the validator to restart from the old snapshot, causing transactions after the snapshot to be discarded.
Risks at the Interface (UI) layer: Bybit's $1.5 billion heist in February 2025 showed that attackers could change the display of wallet addresses on the browser, causing users to sign and approve the wrong transaction. In this case, the immutability (Finality) of the blockchain becomes a barrier that prevents the victim from reclaiming money.
Malicious AI Agent: In 2026, source codes created by AI may contain code that automatically withdraws money, attacking the user's will instead of attacking the protocol.
Comparing Finality between key infrastructures (Update 2026)
Below is a summary of the complete characteristics of the top networks according to analysis by Tan Phat Digital:
Bitcoin: Uses the Probability mechanism (Nakamoto). Actual time is about 60 minutes (for 6 confirmations). The main risk is a 51% attack due to Hashrate centralization.
Ethereum L1: Uses Economic mechanism (SSF). The achieved time is 12 seconds. The main risk is sophisticated MEV attacks before the block is finalized.
Solana: Uses the Votor mechanism. The time achieved is 150 milliseconds. The main risk lies in network outages due to complex software errors.
Arbitrum One: Uses the Layering mechanism. The time is 1-2 seconds for soft confirmation and about 15 minutes for hard confirmation. The main risk is fraud from the Sequencer side or bridge errors.
Polygon AggLayer: Uses Shared State mechanism via ZK proof. Time achieved is almost instantaneous. The main risk lies in the technical complexity of the ZK proof.
Typical Case Study on Finality risk
In order to clarify transaction reversal scenarios, Tan Phat Digital has compiled 10 typical real-life cases that demonstrate the absolute non-absoluteness of Finality:
1. 51% Attack on Monero by Qubic (August 2025)
This is the best example of breaking probabilistic Finality. Mining pool Qubic offered 3x rewards for attracting hashrate, thereby controlling more than 50% of the Monero network. As a result, Qubic performed a chain reorganization (Reorg) up to 6 blocks deep, causing about 60 blocks to be officially removed (orphaned) and transaction history overwritten. This event shows that PoW security depends heavily on economic incentives.
2. Bybit and the theft of 1.5 billion USD via interface error (February 2025)
An attack that does not target the protocol but targets the display (UI) layer. An attacker injected malicious JavaScript code into the Safe{Wallet} interface on Bybit developer's computer. When the manager signs off on the transaction, they believe they are transferring money internally but are actually sending it to the thief's wallet. Once a transaction reaches Finality on Ethereum, immutability makes the amount irrevocable.
3. AWS outage paralyzes Layer 2 (October 20, 2025)
The power outage in the US-EAST-1 region of AWS exposed the weaknesses of centralized sequencers. Layer 2 networks such as Base and Optimism (60-80% dependent on AWS) were completely disrupted. Due to the Sequencer shutdown, transactions cannot be batched and sent to Layer 1, causing the time to reach Hard Finality to be delayed by hours.
4. Software error caused Solana network shutdown (February 6, 2024)
The Solana network was down for nearly 5 hours due to a bug in the LoadedPrograms function that led to an infinite loop. During this time, Finality is completely frozen. Validators had to manually coordinate restarting the network from a snapshot, meaning any transactions that occurred immediately before the outage ran the risk of never being recorded.
5. Polygon Bor RPC Outage (December 2025)
The Polygon PoS network experienced an RPC service outage affecting Bor customers. Although the block is still produced, users cannot access or confirm transaction status through normal portals. This incident shows that although technical Finality is still maintained, "Experiential Finality" is broken, causing confusion for users.
6. Hardware error at Arbitrum One's Sequencer
During 2024, Arbitrum One experienced a Sequencer shutdown for about 2 hours due to a hardware error. During this period, users do not receive Soft Finality (instant confirmation), forcing them to use the direct sending method via Delayed Inbox on Ethereum with higher costs and longer confirmation times.
7. Shibarium Bridge Exploitation (September 2025)
Attackers combined flash loans with taking control of leaked validator keys to extort $2.4 - 4.1 million. By manipulating voting rights, they pushed a fake network update to withdraw funds. This is proof that Finality can be manipulated if the social governance layer and node control is compromised.
8. SwissBorg/Kiln Endpoint Compromise (September 2025)
A third-party attack resulted in the loss of approximately $40 million in SOL value from the SOL Earn program. The attacker changed the transaction path through a hijacked endpoint, tricking the system into automatically signing illegal withdrawal orders. Solana's quick finality in this case helped the thief disperse assets extremely quickly before being detected.
9. Trust Wallet browser malware (December 2025)
A fake extension on the Chrome Web Store collected the recovery phrases (seed phrases) of more than 2,500 wallet addresses, resulting in a loss of 8.5 million USD. Once an attacker has the private key, every transaction they make is technically valid, making it impossible to reverse or recover assets from the wallet developer.
10. Polygon Madhugiri and Reorg De-risking (Late 2025)
In a positive Case Study, Polygon's Madhugiri upgrade introduced the VEBloP block production model. This upgrade reduces Finality time from minutes to ~5 seconds and claims to completely eliminate chain reorganization (Reorg) risk. This is an important step towards making blockchain more trustworthy for large financial institutions like MasterCard and BlackRock.
Frequently Asked Questions (FAQ) about Finality in Blockchain
What is finality and why is it important? Finality is the irreversible confirmation that a transaction has been recorded in the ledger. It is important because it prevents double-spending and creates confidence in financial activities, ensuring assets are not repossessed after they have been moved.
Why is Bitcoin only probabilistic? Because Bitcoin uses Nakamoto consensus, where anyone can mine blocks. If two miners find a block at the same time, the network temporarily branches. Only when there are more blocks on top of it, the probability of the branch containing your transaction being removed gradually approaches 0 but never reaches absolute 0 mathematically.
How does the 51% attack on Monero happen in 2025? Mining pool Qubic lured miners with high rewards, taking control of more than 50% of the hashrate. This allowed them to perform a Reorg up to 6 blocks deep, removing about 60 official blocks of the network, proving that PoW is still vulnerable to economic incentives.
How is Ethereum Single Slot Finality (SSF) different from the current mechanism? Currently Ethereum takes about 12.8 minutes to finalize. SSF aims to kill blocks within the proposed slot (12 seconds), completely eliminating the possibility of Reorg and reducing the risk from short-term MEV attacks.
What is the Horn Protocol in the Ethereum roadmap? This is a solution that uses ZK-SNARK to compress the signatures of millions of validators into a single proof. It allows low-end devices (such as phones) to verify the completeness of the network in an extremely short time.
How does Solana Alpenglow achieve 150ms finality? Alpenglow replaces the old mechanism with Votor (fast two-round voting) and Rotor (stake-weighted live messaging). This allows the network to reach 2/3 stake consensus almost instantly after the block is created.
Is "Optimistic Confirmation" on Solana safe? It is extremely fast (400-800ms) and is sufficient for small transactions. However, it still has an extremely low risk of reversal if the network experiences a serious software failure before reaching Finality.
Distinguish between Soft Finality and Hard Finality on Layer 2? Soft Finality is an instant confirmation from the L2 Sequencer, based on trust in the operator. Hard Finality is achieved when data has been pushed and finalized on Ethereum Layer 1, providing ultimate security.
Why do Layer 2s like Arbitrum have a 7-day "Challenge Window"? This is the amount of time needed for the Optimistic Rollup mechanism so that monitoring nodes can detect and complain about fraud before transactions are considered completely immutable on L1.
How does Economic Finality work? In Proof-of-Stake, completeness is guaranteed by the fact that if someone intentionally reverses the block, they will "slash" (burn) a large amount of the staked assets (for example, at least 1/3 of the total stake on Ethereum), creating a financial barrier too high to implement.
What is the Reorg phenomenon?It is when the network temporarily has two versions of its history. When one version is proven to be "longer" or "heavier", the other version is discarded, causing transactions in the discarded blocks to return to an unconfirmed state.
Can a 51% attack change my wallet balance? Not quite. An attacker can only reverse transactions they have already made (to double-spend) or block new transactions. They cannot create fake transactions from your wallet because they do not have your private key.
How do Verkle Trees affect the finality of Ethereum? Verkle Trees help reduce the storage required for nodes by 90%, making it easier to run full nodes, thereby increasing decentralization and supporting a more secure path to SSF.
Why did Bybit lose 1.5 billion USD even though the Ethereum blockchain has very good Finality? Because the attack took place at the user interface (UI) layer. The attacker tricks the wallet manager into signing a transaction that is technically valid but has misleading remittance content. Once signed and finalized, the immutability of the blockchain makes the money irrevocable.
Which blockchain should users choose based on their need for Finality? If you need absolute security for large assets, choose Ethereum L1. If you need Web2-like payment speeds for games or consumer applications, Solana Alpenglow (2026) is the top choice.
Finality in blockchain is not an eternal constant but an ecosystem of economic probabilities and barriers. Tan Phat Digital draws key conclusions:
Speed and Safety are a trade-off: The fastest networks like Solana are approaching the physical limit (150ms) but require extremely powerful hardware infrastructure, increasing the risk of failure compared to Ethereum's conservative model.
Risk shifts to the application layer: When As the protocol layer becomes increasingly secure, attacks will focus on the interface layer (UI) and AI Agents to trick users into making "valid but erroneous" transactions.
Recommendation: Businesses should apply flexible confirmation policies. Expect to wait at least 12-15 minutes on Ethereum for million-dollar transactions, but 150ms confirmations on Solana are acceptable for everyday consumer activities.
Understanding the "narrow window" of transaction reversals is key to effective risk management in the era of global asset digitization.
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