Bitcoin Core’s development activity shows a reversal in trend, with +60% traffic and 135 unique contributors.
The ecosystem surrounding Bitcoin Core experienced a revival in 2025, marking a clear change of course compared to the negative trend of previous years. Data collected by Jameson Lopp, Chief Security Officer at Casa, reveal an increase in development activity for the software that powers roughly 78% of Bitcoin network full nodes.
According to Lopp’s annual analysis, activity on the Bitcoin Development Mailing List—the primary channel for proposing and discussing protocol changes—rose by 60% compared to 2024. This increase is particularly notable given that the previous year saw a 25% decline, partly attributed to the mailing list’s migration from Linux Foundation servers to Google Groups.
The number of developers actively contributing to the repository grew to 135 individuals in 2025, up from 112 the year before. After peaking at 193 contributors in 2018, participation had steadily declined through most of the early 2020s.
As for the overall volume of code changes—measured in lines added and removed—Bitcoin Core recorded approximately 285,000 lines over the course of the year. This figure is broadly in line with the 276,000 lines logged in 2024 and remains consistent with the project’s historical pace over the past decade.
Lopp also noted that code commits—meaning the changes formally recorded in the software—rose by 1% year over year, reaching 2,541. This confirms the upward trend that began in 2023, following a drop from the peak of nearly 3,500 commits reached in 2021.
The year 2025 proved to be one of intense technical activity for Bitcoin Core. In November, the project completed its first public third-party security audit. Conducted by cybersecurity firm Quarkslab and funded by the non-profit organization Brink, the review focused on Bitcoin Core’s peer-to-peer networking layer and found no critical or high-severity vulnerabilities.
The year also saw heated debates over mempool policy changes, culminating in the integration of an update to OP_RETURN limits in version 30.
Organizations supporting Bitcoin Core development continued their funding efforts as well. VanEck reaffirmed its commitment to allocate 5% of the profits from its spot Bitcoin ETF to the non-profit Brink, which supports protocol developers.
