There is debate about the cause of the filter clogging in the LOX engine intakes that SpaceX reported on integrated flight test (IFT) 2 and 3 of Starship. Although the original design was thought to use pure autogenous pressurization obtained by heating liquid fuel (oxygen and methane) to gas with a heat exchanger connected to the regenerative cooling loop, there is speculation that later designs obtained oxygen gas from the LOX pre-burner exhaust. This exhaust might contain small amounts of CO2 and water, and this has been suggested to cause ice build up inside the LOX tank, clogging of the LOX intake filter, and IFT-2 and -3's subsequent engine failures. Although one of the original proposers of the idea attributed it to observational evidence from NASASpaceFlight (NSF), that seems to have been rejected by NSF reporters themselves. Still, the theory survives as an explanation for the filter clogging.

https://www.reddit.com/r/SpaceXLounge/comments/1b1u1xl/does_raptor_engines_use_preburner_exhausts_to/

This market will resolve if reliable information becomes public before 2026-May-25 about whether either IFT-2 or IFT-3 used pre-burner exhausts to pressurize Starship tanks. If by 2026-May-25 there is no direct confirmation either way from SpaceX employees, nor new direct conclusive evidence, the market will close unresolved. I will run a poll if there is debate about the state of the evidence at that time.

Note: this market resolves based on whether either IFT-2 or -3 used preburner exhaust as a source of pressurization gases, not any downstream questions about the source of engine failure. Use of preburner exhaust in either test flight is sufficient to resolve as "yes".

EDIT (resolution): Elon Musks confirms that pre-burner exhaust was used to pressurize LOX tanks in EverydayAstronaut video. Available on YouTube tomorrow (June 22) and on Patreon now: https://www.patreon.com/EverydayAstronaut