Is BSL-1.0 compatible with LGPL-2.1?
Yes.
Permissive code coexists; copyleft scoped to the copyleft files/library. Result license is the more restrictive of the inputs. You must satisfy every input license's notice and source-offer terms. Verify pairwise compatibility first.
Resulting work's license: LGPL-2.1-only
General guidance, not legal advice.
Obligations when redistributing as open source
- BSL-1.0: retain the copyright notice and license text in source distributions (not required for binary-only).
- LGPL-2.1: retain the copyright notice and license text.
- LGPL-2.1: state significant changes made to the code.
- LGPL-2.1: publish the source of any modifications to the library itself.
- LGPL-2.1: modifications to the library must remain under LGPL-2.1.
Other distribution models
The verdict is the same under every distribution model; the obligations differ. Check this pair in the tool to switch models.