In September 2020, the Czech defence ministry certificated the L-39NG using supranational military standards..[2] In October 2024, as the company reached serial production, the type was officially named as Skyfox.

The Stage 1 programme is an upgrade that is available to existing L-39 operators; the original airframes are retrofitted with a new engine and (optionally) modern avionics.

The Stage 2 programme involves the production of new-build aircraft; these benefit from several design improvements, such as the use of a wet wing, eliminating the original L-39's distinctive wingtip fuel tanks.

[10] On 14 March 2018, the company announced that the L-39CW had received type certification, signifying its airworthiness and readiness for serial manufacture.

[13][14] The new airframe is considerably lighter and produces less drag, overall, the redesigned aircraft was said to have comparable operating costs to contemporary turboprops.

[18][19][20] In April 2018, a partnership agreement was signed between Aero Vodochody and Israel Aerospace Industries (IAI) for the integration of the latter's virtual training solutions onto the L-39NG, in addition to jointly working on other projects.

[26] The technology demonstrator L-39CW, a conventional airframe outfitted with the FJ44-4M engine and other retrofitted elements, performed its first flight from Vodochody airport on 14 September 2015.

[13][27] In September 2016, Aero Vodochody announced that it had completed the first phase of testing with the L-39CW, and was now ready to proceed with the development of the more comprehensive new-build L-39NG.

[24][29] In 2019, it was announced that Aero Vodochody was changing the L-39NG's certification schedule, this was reportedly in response to customer demands for increased capability; the move was to facilitate the clearance of deliveries in the full trainer configuration during the latter part of 2020, whereas the earlier intent had been to secure approval for a basic standard sometime in late 2019.

[30] On 25 May 2020, the L-39 Skyfox commenced static fatigue testing, one reported aim of which is to validate the new airframe's operating life of 5,000 flight hours.