Apparently he didn't. Here's what Grok says:

No, Tyler Robinson did not enter a guilty plea as of October 2, 2025. He is the 22-year-old suspect charged with aggravated murder and six other felonies in the September 10, 2025, shooting death of conservative activist Charlie Kirk at Utah Valley University. During his initial court appearance on September 16, 2025, in Utah's Fourth District Court, Robinson did not enter any plea and was held without bail. His defense team requested more time to review evidence before deciding on a preliminary hearing, with a waiver hearing scheduled for September 29, 2025. An arraignment—where a formal guilty or not guilty plea would typically be entered—has not yet occurred, and no updates indicate one since then. Prosecutors are seeking the death penalty, and the case is progressing toward a potential trial in 2026 or later.

Also, btw - Grok is REALLY good for quick summaries of recent events. Not that it's always the truth, but for stuff like this, simple matters of fact, it's pretty good.