GPT-5.5 said its cutoff was June 2024

What happened

On Hacker News, on the thread “OpenAI releases GPT-5.5 and GPT-5.5 Pro in the API”, user czk posted (2026-04-24 19:16 UTC):

API page lists the knowledge cutoff as Dec 01, 2025 but when prompting the model it says June 2024.

Knowledge cutoff: 2024-06
Current date: 2026-04-24

You are an AI assistant accessed via an API.

When other users asked, czk tested a later event and reported the answer “Donald Trump won the 2024 U.S. presidential election.” (with thinking and tools disabled). czk added that the model “obviously knows things after the reported date but its just curious that it reports that date consistently.”

Why this is striking

• The model underclaims its own knowledge. This mirrors cases 006/008 (older model names). Its self-image is older than what it actually knows.
• In the thread, users speculated that an old self-reported cutoff might be deliberate, to push the model to search. That is unverified.
• A model that believes its cutoff is June 2024 will treat anything from mid-2024 to Dec 2025 as “after my cutoff”, even events it actually knows about. That makes it more likely to wrongly doubt real events.

Correction

None needed for facts. The self-report stayed wrong.

Lesson

Don’t rely on a model’s self-reported cutoff. Measure it (see research.md: Dated Data, LLMLagBench), and give the model its real cutoff and today’s date explicitly.

Sources

• Hacker News comment by czk: news.ycombinator.com