The WikiPedia article lists the aerospike design as the original intended powerplant from Firefly Space Systems. The Firefly Aerospace "Revised Firefly Alpha" reportedly has a bigger payload and higher cost per launch.
The Firefly Aerospace site shows the following:
PROPULSION: STAGE 1
Engine / 4X Reaver 1
Propellant / LOX / RP-1
Propelleant Feed / Turbopump
Combustors / 4
Thrust (vac) / 728.8 kN (163,841 lbf)
lsp (vac) / 295.7 seconds
and
PROPULSION: STAGE 2
Engine / Lightning 1
Propellant / LOX / RP-1
Propelleant Feed / Turbopump
Combustors / 1
Thrust (vac) / 69.9 kN (15,714 lbf)
lsp (vac) / 324.1 sec
and states:
Alpha utilizes well established propulsion technology. Both stages use
common designs: copper regen-cooled LOx/RP-1 thrust chambers, a simple tap-off
cycle which drives single shaft turbopumps, nozzle-mounted turbine exhaust
manifolds, and hydraulic actuators. Innovations in Firefly engines include our
simple “Crossfire” injector, tap-off geometry, dual-mounted electrically
actuated, trim-able propellant main valves, and ultra-compact horizontal
turbopump mounting. The upper stage engine, “Lightning,” includes a turbine
exhaust cooled refractory metal high area ratio nozzle extension. The first
stage “Reaver” engines feature simple single axis gimballing. Consistent with
the overall Alpha vehicle design, cost and performance are traded and optimized
in Lightning and Reaver components to provide the best payload performance
value.
so it indeed does appear the new design no longer uses the aerospike engines.
Interestingly, if you modify the URL http://www.fireflyspace.com/vehicles/firefly-a to http://www.fireflyspace.com/vehicles/firefly-b you get a page from the old Firefly Space Systems site showing the design of the original proposed Firefly Beta.