Underneath this test mule purporting to be a convertible Lexus IS-F is actually the next-generation version of the firm’s new IS, due on sale next year.

Lexus has confirmed that an IS-F cabrio is not in the current product plan, and the car was acting as a test mule for another model.

US media who saw the mule up close at its test session at the Nürburgring last week report that there were a number of clues that gave away its identity. Chief among these were the aluminium lower control arms of the test car’s rear suspension. The current IS and IS-F use steel. The new GS, on which the next-gen IS will be substantially based, uses aluminium for the multi-link rear suspension and has the option of rear-wheel steer.

The next-gen IS and the current GS are understood to have been developed largely in parallel, so expect many of the innovations of Lexus’s latest 5-series rival to carry over to the smaller model.

Lexus’s former product planning chief, Karl Schlicht, said earlier this year: “The new GS leads to the new IS.”

Features of the new IS are expected to include a stiffer bodyshell, multi-link front suspension, wider tracks and a new look designed to give Lexus’s small saloon greater visual presence.

Don’t expect four-cylinder diesel power to make it into the new IS, however, as Lexus is adamant that hybrids offer similar benefits. The firm is known to be working on a new four-cylinder petrol-electric powertrain that could appear first in the IS.