Throughout the API documentation, new classes and methods are indicated with a disclaimer "Since: version 2.3."

Several new classes and features have been introduced, notably

New Stereochemistry classes
New Substructure Search classes
Improved Conformer Searching searching
OBChargeModel - Cleaner interface for assigning partial charges using different models
OBGraphSym - Cleaner interface for computing the stereochemical symmetry classes
OBSpectrophore - A new powerful descriptor for screening bioactive molecules
OBDepict - 2D depiction

In addition, a wide variety of new plugins are available, including

computation of partial charges using GasteigerCharges, MMFF94Charges, QEqCharges, and QTPIECharges
"diverse" conformer searching
etc.