Lesson 1061 of 1570
Why Claude Doesn't Know What Happened Last Week
Models have a 'knowledge cutoff' — a date after which they know nothing without web search.
Lesson map
What this lesson covers
Learning path
The main moves in order
- 1The big idea
- 2knowledge cutoff
- 3training data
- 4stale info
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Section 1
The big idea
Every model was trained on data up to a specific date — its 'knowledge cutoff.' After that date, the model knows nothing on its own. Ask it about today's news and it'll either say 'I don't know' or (worse) hallucinate. The fix: use a model with web search turned on (Perplexity, ChatGPT with search, Claude with web).
Some examples
- Claude Opus 4.5 cutoff: ~April 2024. Anything from after is unknown without search.
- GPT-5 cutoff: ~April 2025. Slightly newer, same problem.
- Gemini 2.5 cutoff: ~mid-2024. Same problem.
- Web search turns this off — Perplexity, ChatGPT 'Search', Claude 'Web Search' are all 2026-current.
Try it!
Ask Claude or ChatGPT (without search) about a news story from this week. Watch what it does. Then turn on search and ask again.
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