business source license (BSL)

BSL (sometimes BUSL) is a time-decaying, source-available license that transitions to open source, usually after 3–4 years. It is designed to protect commercialization during early growth phases.

1. Source code is publicly available and you can generally copy, modify, and create derivative works for non-production uses (e.g., evaluation, internal testing, development).​
2. Commercial production use is restricted by default and only allowed if your use fits within an “Additional Use Grant” defined by the licensor, or if you obtain a commercial license.​
3. The licensor can define which kinds of users or use cases are prohibited (for example, offering a competing hosted service using the software).​

A defining feature is that each version of the software must convert to an open source license (GPL-compatible) after a specified period, up to a maximum of four years from that version’s first public release. This is sometimes called a “springing license” because the code for older versions eventually becomes fully open source under the designated “Change License.”