Mellde and Sason decided to use glass-reinforced plastic for the construction of the car's body, a material which had little to no use in automobile manufacturing at the time.

Featuring a three-cylinder 748 cc two-stroke engine generating 57.5 horsepower (42.9 kW), the Sonett I was an advanced low-weight 600 kg (1,323 lb) racer based on aircraft design concepts.

[4] With a projected top speed of 190 km/h (120 mph), the Sonett I had the prospect of success on the European race circuit, and a production run of 2,000 units was planned for 1957.

However, the competition rules changed, permitting modified production cars into the race classes which Saab had envisioned for its purpose-built Sonett, and the economic and marketing viability of the project faded.

1" and built with a manually crafted glass-reinforced plastic (GRP, or "fiberglass") body, served as the reference model for the other five cars.

[6] In September 1996, rally driver Erik Carlsson broke the Swedish record for the under–750-cc engine class with a speed of 159.4 km/h (99.0 mph) in the restored Sonett I prototype "No.

The demands from the dealers included a targa top roof, wind-up windows, a heater as standard equipment and good handling.

was put into limited production in 1966 as the Sonett II, manufactured at the Aktiebolaget Svenska Järnvägsverkstäderna (ASJ) in Arlöv.

[11][12] The additional weight did require some strengthening of the chassis and suspension pieces, and the wheels were half an inch wider than the four-inch units used on the Sonett II.

When Saab started using the Ford Taunus V4 engine in their 95, 96, and Monte Carlo models, an upgrade for the low-volume Sonett II became economically feasible.

A new "bulge" hood, designed by Gunnar A. Sjögren, was required to clear the larger V4 engine, with a slight right offset to avoid obstructing the driver's view.

This asymmetrical hood shape, criticized by both the automotive press and within Saab itself, contributed to the motivation for the 1970 Sonett III redesign.

However, Saab tasked its own designer, Gunnar A. Sjögren in order to make the car fit the existing Sonett II chassis without the expensive manufacturing-line changes.

With the mandate for a "bulge-less" hood, the engine compartment opening evolved into a small front popup panel, resulting in more limited access than in the Sonett V4.

US safety regulations required new low speed impact proof bumpers after 1972, significantly detracting from its Italian-inspired design.

While the same 1500 cc Ford Taunus V4 engine as the Sonett V4 remained available for the 1970 and 1971 model years, emission control requirements reduced the available horsepower.

However the project was brought to an end when the board at Saab rejected the proposals, when Kjellberg presented Reliant's business plan for the new Sonett.