The Open Source Initiative has formally approved the license used by curl, giving the widely deployed data-transfer project an official designation that its maintainer says was absent for decades despite the license’s close relationship to the MIT license.
Curl founder and lead developer Daniel Stenberg said the approval took effect on April 17, 2026. He disclosed the milestone months later, explaining that he had only recently realized the process had been completed. The result does not represent a new licensing switch for curl. Instead, it confirms the status of the text the project has already used for years.
Curl’s licensing history began with the GNU General Public License, inherited from its predecessor, httpget. The project moved to the Mozilla Public License in October 1998. In 2001, it offered the MIT license as an additional option because the MPL created compatibility concerns for some users, particularly in relation to GPL-licensed software.
The project dropped the MPL option in 2002 and intended to proceed under MIT terms. Around that time, however, Stenberg made a small alteration to the standard MIT text. That modification meant the resulting license was technically not the canonical MIT license, even though curl’s community continued to describe it that way informally and treated its practical effect as similar.
The distinction became more visible through the SPDX project, which assigns standardized identifiers to licenses used in software packages and compliance tools. SPDX classified curl’s text separately rather than treating it as identical to MIT. The project-specific wording subsequently became known as the curl license.
That separate identity created a modest documentation and recognition problem. Developers generally understand the permissions associated with MIT, but a project-specific license does not automatically carry the same familiar label. According to Stenberg, neither the Free Software Foundation nor the Open Source Initiative had previously provided the curl license with the corresponding formal recognition. He said the lack of an OSI designation did not appear to cause meaningful adoption problems, and he was not aware of serious doubt about whether the terms were open source.
The approval therefore functions mainly as authoritative confirmation for users, distributors and compliance systems. It gives organizations a recognized basis for classifying curl’s actual license text without pretending that it is word-for-word MIT. It also resolves an administrative consequence of a minor drafting decision made when software-license metadata and automated identification were far less prominent.
For curl, the outcome is a belated checkmark rather than a change in how the software can be used. The project keeps its established terms, while developers and legal-review teams gain a clearer, formally approved name for them.
