Author: Pan Zhixiong

The annual summary of Bitcoin Optech has always been regarded as a technical barometer of the Bitcoin ecosystem. It does not focus on price fluctuations but records the most authentic pulse of the Bitcoin protocol and key infrastructure.

The 2025 report reveals a clear trend: Bitcoin is undergoing a paradigm shift from "passive defense" to "active evolution."

Over the past year, the community has moved beyond merely patching vulnerabilities and has begun to systematically address existential threats (such as quantum computing), while radically exploring the boundaries of scalability and programmability without sacrificing decentralization. This report is not only a memorandum for developers but also a key index for understanding the asset attributes, network security, and governance logic of Bitcoin over the next five to ten years.

Core Conclusions

Looking back at 2025, the technological evolution of Bitcoin presents three core characteristics, which are also the keys to understanding the following ten major events:

1. Proactive Defense: The defense roadmap against quantum threats has become clear and practical for the first time, extending security thinking from the "present" to the "post-quantum era."
2. Functional Layering: The high-density discussions of soft fork proposals and the "hot-plug" evolution of the Lightning Network show that Bitcoin is achieving the architectural goal of "solid foundation below, flexibility above" through layered protocols.
3. Infrastructure Decentralization: From mining protocols (Stratum v2) to node validation (Utreexo/SwiftSync), a significant amount of engineering resources has been invested in lowering participation barriers and enhancing censorship resistance, aiming to counteract the centralizing forces of the physical world.

The annual report of Bitcoin Optech covers hundreds of thousands of code submissions, email group debates, and BIP proposals over the past year. To extract the true signals from the technical noise, I have filtered out updates limited to "local optimizations" and selected the following ten events that have a structural impact on the ecosystem.

1. Systematic Defense Against Quantum Threats and "Fortification Roadmap"

[Status: Research and Long-term Proposal]

2025 marks a qualitative change in the Bitcoin community's attitude towards the threat of quantum computing, shifting from theoretical discussions to engineering preparations. BIP360 has been numbered and renamed to P2TSH (Pay to Tapscript Hash). This is seen as an important stepping stone in the quantum fortification roadmap and serves more generally for certain Taproot use cases (such as commitment structures that do not require internal keys).

At the same time, the community has delved into more specific quantum-safe signature schemes, including constructing Winternitz signatures with OPCAT under the premise of introducing corresponding script capabilities in the future (such as reintroducing OPCAT or adding new signature operation codes), discussing STARK verification as a native script capability, and optimizing on-chain costs for hash signature schemes (such as SLH-DSA / SPHINCS+).

This topic occupies the top position because it touches on the mathematical foundation of Bitcoin. If quantum computing indeed weakens the elliptic curve discrete logarithm assumption (thereby threatening the security of ECDSA/Schnorr signatures), it will trigger systemic migration pressure and historical output security layering. This forces Bitcoin to prepare upgrade paths in advance at the protocol and wallet levels. For long-term holders, choosing custodial solutions with upgrade roadmaps and security audit cultures, as well as paying attention to potential migration windows in the future, will become essential for asset preservation.

2. Explosion of Soft Fork Proposals: Building the Foundation for "Programmable Vaults"

[Status: High-density Discussion / Draft Stage]

This year has seen a high-density discussion of soft fork proposals, focusing on how to release the expressive power of scripts while maintaining minimalism. Contract proposals such as CTV (BIP119) and CSFS (BIP348), as well as technologies like LNHANCE and OPTEMPLATEHASH, are attempting to introduce safer "restrictive clauses" to Bitcoin. Additionally, OPCHECKCONTRACTVERIFY (CCV) has become BIP443, and various arithmetic operation codes and script recovery proposals are also waiting for consensus.

These seemingly obscure upgrades are, in fact, adding new "physical laws" to the global value network. They are expected to make native "vault" constructs simpler, safer, and more standardized, allowing users to set mechanisms for delayed withdrawals and revocation windows, thus achieving "programmable self-preservation" from the perspective of protocol expressiveness. At the same time, these capabilities are expected to significantly reduce the interaction costs and complexity of second-layer protocols like the Lightning Network and DLC (Discrete Log Contracts).

3. "Censorship-Resistant" Reconstruction of Mining Infrastructure

[Status: Experimental Implementation / Protocol Evolution]

The decentralization of the mining layer directly determines Bitcoin's censorship resistance. In 2025, Bitcoin Core 30.0 introduced an experimental IPC interface, significantly optimizing the interaction efficiency between mining pool software/Stratum v2 services and Bitcoin Core validation logic, reducing reliance on inefficient JSON-RPC, and paving the way for the integration of Stratum v2.

One of the key capabilities of Stratum v2 is to further decentralize transaction selection from mining pools to more distributed miners (when mechanisms like Job Negotiation are enabled), thereby enhancing censorship resistance. Meanwhile, the emergence of MEVpool attempts to address the MEV issue through blinded templates and market competition: ideally, multiple marketplaces should coexist to avoid a single point of market becoming a new centralized hub. This directly relates to whether ordinary users' transactions can still be fairly packaged in extreme environments.

4. Immune System Upgrade: Vulnerability Disclosure and Differential Fuzzing

[Status: Ongoing Engineering Operations]

The security of Bitcoin relies on self-examinations before real attacks. In 2025, Optech recorded numerous vulnerability disclosures against Bitcoin Core and Lightning implementations (such as LDK/LND/Eclair), covering issues from fund locking to privacy de-anonymization, and even severe theft risks. This year, Bitcoinfuzz utilized "Differential Fuzzing" technology to identify over 35 deep bugs by comparing different software responses to the same data.

This high-intensity "stress testing" is a sign of ecosystem maturity. It acts like a vaccine; while it exposes issues in the short term, it significantly enhances the system's immunity in the long run. For users relying on privacy tools or the Lightning Network, this also serves as a wake-up call: no software is absolutely perfect, and keeping key components updated is the simplest rule for ensuring the safety of deposits.

5. Lightning Network Splicing: "Hot Updates" of Channel Funds

[Status: Cross-Implementation Experimental Support]

The Lightning Network achieved a significant breakthrough in usability in 2025: Splicing (dynamic channel updates). This technology allows users to dynamically adjust funds (deposit or withdraw) without closing the channel, and it currently has experimental support in the three major implementations: LDK, Eclair, and Core Lightning. Although the related BOLTs specifications are still being refined, significant progress has been made in cross-implementation compatibility testing.

Splicing is the key capability of "adding or subtracting funds without closing the channel." It is expected to reduce payment failures and operational friction caused by inconvenient channel fund adjustments. Future wallets are expected to significantly lower the learning costs of channel engineering, allowing more users to use LN as a payment layer close to a "balance account," which is a key piece in Bitcoin payments moving towards large-scale daily use.

6. Verification Cost Revolution: Running Full Nodes on "Consumer Devices"

[Status: Prototype Implementation (SwiftSync) / BIP Draft (Utreexo)]

The moat of decentralization lies in verification costs. In 2025, SwiftSync and Utreexo launched a direct impact on the "full node threshold." SwiftSync optimizes the UTXO set writing path during IBD (Initial Block Download): it only adds to the chainstate when confirming that an output remains unspent at the end of IBD, and with a "minimal trust" hints file, it accelerated the IBD process by over 5 times in sample implementations while opening up space for parallel verification. Utreexo (BIP181-183), on the other hand, allows nodes to verify transactions without locally storing the complete UTXO set through a Merkle forest accumulator.

The advancement of these two technologies means that running full nodes on resource-constrained devices will become feasible, increasing the number of independent validators in the network.

7. Cluster Mempool: Reshaping the Underlying Scheduling of the Fee Market

[Status: Near Release (Staging)]

In the anticipated features of Bitcoin Core 31.0, the implementation of Cluster Mempool is nearing completion. It introduces structures like TxGraph, abstracting complex transaction dependencies into a "transaction cluster linearization/sorting" problem that can be efficiently solved, making block template construction more systematic.

Although this is an upgrade to the underlying scheduling system, it is expected to enhance the stability and predictability of fee rate estimation. By eliminating abnormal packaging orders caused by algorithmic limitations, the future Bitcoin network is expected to perform more rationally and smoothly during congestion, and users' accelerated transaction requests (CPFP/RBF) can also take effect under more certain logic.

8. Fine-tuning Governance of the P2P Propagation Layer

[Status: Policy Update / Ongoing Optimization]

In response to the surge of low-fee transactions in 2025, the Bitcoin P2P network experienced a strategic turning point. Bitcoin Core 29.1 lowered the default minimum relay fee to 0.1 sat/vB. Meanwhile, the Erlay protocol continues to advance to reduce node bandwidth consumption; additionally, the community has proposed "block template sharing" and continues to optimize compact block reconstruction strategies to cope with the increasingly complex propagation environment.

With more consistent policies and lower default thresholds for nodes, the feasibility of low-fee transactions propagating through the network is expected to improve. These directions are expected to lower the rigid bandwidth requirements for running nodes, further maintaining the fairness of the network.

9. OP_RETURN and the "Tragedy of the Commons" Debate on Block Space

[Status: Mempool Policy Change (Core 30.0)]

Core 30.0 relaxed the policy restrictions on OP_RETURN (allowing more outputs and removing some size limits), which sparked intense philosophical debates about the use of Bitcoin in 2025. Note that this pertains to Bitcoin Core's Mempool Policy (default forwarding/standard policy) rather than consensus rules; however, it will significantly affect whether transactions are easily propagated and seen by miners, thus genuinely impacting the competitive landscape of block space.

Supporters believe this can correct incentive distortions, while opponents worry it may be seen as an endorsement of "on-chain data storage." This debate reminds us that the rules for using block space, as a scarce resource, are also the result of ongoing negotiations among various interests, even at a non-consensus level.

10. Bitcoin Kernel: "Componentized" Reconstruction of Core Code

[Status: Architectural Reconstruction / API Release]

In 2025, Bitcoin Core took a key step towards architectural decoupling by introducing the Bitcoin Kernel C API. This marks the separation of "consensus verification logic" from the large node program, turning it into an independent, reusable standard component. Currently, this kernel can support external projects in reusing block validation and chain state logic.

"Kernelization" will bring structural security dividends to the ecosystem. It allows wallet backends, indexers, and analytical tools to directly call official verification logic, avoiding the risk of consensus discrepancies caused by reinventing the wheel. This is akin to providing the Bitcoin ecosystem with a standardized "factory engine," making various applications built on it more robust.

Appendix: Mini-Glossary

To assist with reading, here are brief definitions of key terms in the text:

• UTXO (Unspent Transaction Output): The basic unit of the Bitcoin ledger state, recording who owns how much currency.
• IBD (Initial Block Download): The process of synchronizing historical data when a new node joins the network.
• CPFP / RBF: Two transaction acceleration mechanisms. CPFP (Child Pays for Parent) pulls old transactions with new transactions; RBF (Replace-By-Fee) directly replaces low-fee transactions with high-fee transactions.
• Mempool: A buffer where nodes store "broadcasted but not yet packed into blocks" transactions.
• BOLTs: A series of technical specifications for the Lightning Network (Basis of Lightning Technology).
• MEV (Maximal Extractable Value): The maximum extractable value, referring to the additional profits miners can gain by reordering or censoring transactions.

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