Potentially breaking bug fix: Sass numbers are now universally stored as 64-bit floating-point numbers, rather than sometimes being stored as integers. This will generally make arithmetic with very large numbers more reliable and more consistent across platforms, but it does mean that numbers between nine quadrillion and nine quintillion will no longer be represented with full accuracy when compiling Sass on the Dart VM.
Potentially breaking bug fix: Sass equality is now properly [transitive]. Two numbers are now considered equal (after doing unit conversions) if they round to the same 1e-11th. Previously, numbers were considered equal if they were within 1e-11 of one another, which led to some circumstances where $a == $b and $b == $c but $a != $b.
Potentially breaking bug fix: Various functions in sass:math no longer treat floating-point numbers that are very close (but not identical) to integers as integers. Instead, these functions now follow the floating-point specification exactly. For example, math.pow(0.000000000001, -1) now returns 1000000000000 instead of Infinity.
Emit a deprecation warning for $a -$b and $a +$b, since these look like they could be unary operations but they're actually parsed as binary operations. Either explicitly write $a - $b or $a (-$b). See https://sass-lang.com/d/strict-unary for more details.

Add an optional argumentName parameter to SassScriptException() to make it easier to throw exceptions associated with particular argument names.
Most APIs that previously returned num now return double. All APIs continue to accept num, although in Dart 2.0.0 these APIs will be changed to accept only double.