Near synonym for command economy would be centrally planed economy as technically just 'planned economy' is more of an umbrella term, although colloquially when people talk about planned economy they just shorten the centrally planned economy.
An example of an economy satisfying all 3 requirements is North Korea. It has both been around for some time. It satisfies academic definitions of command economy. It is modern example as it still exists in 21st century.
However, one has to be careful about Chinese doublespeak. Chinese officials claim China is socialist country, yet even an economics undergraduate student would be easily able to classify China as mixed but predominantly market economy, and their economy would not satisfy the definitions of socialism in authoritative sources. Hence its unclear how much you can take what Xi Jinping is saying at face value. It might all be doublespeak.
An authoritative* definition of command economy is (see Ericson 2007):
A command economy is one in which the coordination of economic activity, essential to the viability and functioning of a complex social
economy, is undertaken through administrative
means – commands, directives, targets and
regulations – rather than by a market mechanism A complex social economy is one involving multiple significant interdependencies among economic agents, including significant division of labour and exchange among production units,
rendering the viability of any unit dependent on
proper coordination with, and functioning of,
Economic agents in a command economy, and
in particular production organizations, operate
primarily by virtue of specific directives from
higher authority in an administrative/political
hierarchy, that is, under the ‘command principle’.
Thus the life cycle and activity of enterprises and
firms, their production of output and employment
of resources, adjustment to disturbances, and the
coordination between them are primarily
governed by decisions taken by superior organs
responsible for managing those units’ roles in the
economic system. One of the most distinctive
features of such an economy is the setting of the
firm’s production targets by higher directive, often
in fine detail. The administrative means used
include planning, material balances, quotas,
rationing, technical coefficients, budgetary controls and limits, price and wage controls, and
other techniques aimed at limiting the discretion
of subordinate operational units/firms. The command principle strives to fully and effectively
replace the operation of market forces in the key
industrial and developmental sectors of the economy, and render the remaining (peripheral) markets manipulable and subordinate to political
direction. Thus the command principle is likely
to clash with the operation of market forces, yet a
command economy may nonetheless contain and
rely on the market mechanism in some of its
sectors and areas, for example, influencing labour
allocation, or stimulating small-scale private production of some consumables.
An authoritative* definition of planned economy (Nove 1987):
Its economy that predominantly relies on
deliberate actions of public authorities, primarily the
The distinction here is that a 'planned economy' is an umbrella term that may include range of things ranging from
indicative planning, when the state uses influence, subsidies, grants, taxes, but does not compel
to Soviet style central planning known also as
‘directive planning’ or command planning. The authorities issue
binding instructions to subordinate management,
telling it what goods and services to provide, from
whom to obtain the required inputs, and, as we
shall see, much else besides
Centrally planed economy is pretty much synonym for command economy (see Ericson 2007), but planed economy itself is more of an umbrella term. This being said when people usually say 'planned economy' they colloquially refer to 'centrally planned economy' (at least that is my experience from various conferences, universities etc).
Question: Are there any examples of modern, stable "command economies"?
Yes there is an example. North Korea.
- it is a command economy following the authoritative academic definition.
- it is stable. Your definition of stable is bit vague, but I would say North Korea was around long enough "that we can see how well it worked"
- it is modern, in a sense it does exist in 21st century.
Why Politics SE and not History SE?:
Why not Economics.SE? This seems to be an economics question.
* both of the sources are also entries in the Palgrave Dictionary of Economics which is considered to be the most academic and accurate dictionary of economics. However, note its not classic dictionary it is a reference to articles that use widely established definitions or discuss how definition change within profession.