The regulations include a test to stop teams exceeding 16:1, but the checks happen at “ambient temperature.” Some rival teams have suggested Mercedes found a way for components to behave differently when they heat up during use, beating the test, though Mercedes says its engine is fully legal.
The compromise announced Saturday means the compression ratio will be controlled in both hot and cold conditions from June 1 and only when hot from the 2027 season thereafter.
There are seven F1 races before the June 1 test.
“The regulations introduced for 2026 represent one of the biggest changes in recent memory,” the FIA said. “All parties acknowledge that with the introduction of such significant regulatory changes, there are collective learnings to be taken from pre-season testing and the initial rounds of the 2026 championship.
“Further evaluation and technical checks on energy management matters are ongoing.”
Mercedes also supplies McLaren, Alpine and Williams.
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