While it should be backwards compatible, there have been enough back-end changes one should test to ensure nothing is broken. The test suite was added to, not altered, but no test suite has 100% coverage.
The 2 biggest changes: adding roll modifier syntax, and chaining the backend to use typescript.
The roll modifier syntax allows roll authors to specify when to re-roll, explode, keep, or drop results from a roll set. There's both a verbose and concise syntax for all 4 types.
An example of use is when generating DnD characters using roll 4, drop worst: 4d6:DL1.
Or the more favorable re-roll ones once, and then drop the lowest: 4d6{ reroll 1x; drop lowest 1 }
The conversion to typescript prevented many errors from seeping through, and will provide dividends as the syntax gets (potentially) more complex. This also means that it should be easier to implement one's own dice result resolver or tree walker.
Oh, also GitHub actions where added so you don't have to just take my work on the tests passing.