Various embodiments concern a handheld beverage container. The beverage container includes a vacuum chamber located radially between an inner tubular sidewall and an outer tubular sidewall and axially between an inner bottom wall and an outer bottom wall. The combined heat capacity of both of the inner tubular sidewall and the inner bottom wall can be greater than the combined heat capacity of both of the outer tubular sidewall and the outer bottom wall such that a vacuum insulated thermal reserve is formed. Heat can be exchanged between the thermal reserve and the beverage to stabilize the temperature of the beverage to counteract ambient cooling/heating of the beverage. Various embodiments concern a cap that seals with a disposable cup that is held within a container body, allowing a beverage to be contained in the disposable cup while being insulated by the container body, with or without a thermal reserve.