Cal Abandons Open Source: AI Forces a Strategic Shift

Cal opts for a proprietary license in response to AI threats

Cal, a once open-source planning application, has recently announced its transition to a proprietary license. This decision, driven by security risks associated with artificial intelligence, marks a significant turning point for the company, which had initially embraced open source as a core principle.

Bailey Pumfleet, CEO of Cal, explained that the inherent transparency of open-source code allows AI tools to more easily detect vulnerabilities, thereby compromising the security of professional users. Despite criticism from the open-source community, Cal has also introduced Cal.diy, an open version aimed at the general public, while emphasizing the growing pressure from AI on the free software ecosystem.

A paradigm shift driven by security

In a video released on April 15, 2026, Pumfleet announced that Cal would migrate from the AGPL license to a closed license. This turnaround is particularly surprising given that open source has been a pillar of the company since its founding in 2022. Although Anthropic's Mythos model is not directly responsible for this change, AI is the primary driving force.

Pumfleet emphasized that the security of free software has historically relied on the community's vigilance to identify and fix vulnerabilities. However, this transparency is now being exploited by attackers using AI tools to detect weaknesses. Models like Claude Opus can already analyze source code and effectively extract vulnerabilities.

He compared the distribution of open-source code to handing over the blueprints of a safe, stating that the number of hackers seeking to exploit these vulnerabilities has significantly increased. For Cal, cybersecurity has become a matter of survival, as the company handles sensitive data and can no longer bear the constant cost of fixing flaws.

Mixed reactions from the community

To accompany this transition, Cal announced the launch of Cal.diy, an open version for enthusiasts and self-hosters. However, the date for this transition has not yet been communicated. Reactions from the community have been harsh, with many users criticizing the decision to move to a closed model, arguing that it would only delay the inevitable without enhancing security.

Pumfleet remains firm in his stance, asserting that AI makes almost everything exploitable. He cites data from Hex Security, indicating that open-source software is five to ten times more vulnerable than its proprietary counterparts.

An impact on the entire open-source ecosystem

Beyond Cal's case, the entire open-source ecosystem is affected by the rise of AI. AI agents are flooding public repositories with automatically generated pull requests, often unnecessary or incorrect, which becomes a mental and technical burden for volunteer maintainers.