Quick answer
A reasoning model is an AI that thinks step-by-step before answering. Models like OpenAI o1, o3, and Claude's "extended thinking" mode spend longer working through a problem before responding. They are slower and more expensive than chat models, but dramatically better at math, coding, and multi-step logic. Worth the wait for hard problems.
In late 2024, OpenAI released o1 — a new kind of AI that takes 10-60 seconds to respond instead of a fraction of a second. It seemed like a step backward. Then people saw the results: dramatic improvements on math, code, and complex reasoning. By 2026, "reasoning models" are a standard category every major AI lab offers. Here is what makes them different.
How does a reasoning model differ from a chat model?
A regular chat model (like GPT-4o, Claude Sonnet) responds immediately. It generates words one at a time based on patterns it learned in training. Fast, fluent, useful for everyday questions.
A reasoning model first "thinks" — generating an internal chain of thought, exploring options, checking work, sometimes backtracking — before producing a final answer. The user sees only the final result, but the model has spent extra compute internally working through the problem.
When should you use a reasoning model?
- Math problems — they get them right where chat models often fail
- Multi-step coding — refactoring, complex bug hunting, system design
- Logic puzzles and planning — where one wrong assumption breaks everything
- Scientific or research questions requiring careful synthesis
- Strategic analysis — multiple variables, tradeoffs, second-order effects
When NOT to use a reasoning model?
- Simple questions and quick lookups — overkill, just wastes time
- Casual conversation or brainstorming — they feel stiff
- Tasks where speed matters more than correctness
- Quick code completions — chat models are faster
Cost note: reasoning models charge per "thinking token" too, not just final output. A complex question in o3 can cost 10-30x what GPT-5 charges. Use them deliberately, not by default.
Which reasoning models are available in 2026?
OpenAI: o3, o3-mini, o4. Anthropic: Claude Opus 4.7 with "Extended Thinking" mode toggle. Google: Gemini Ultra 2.0 with thinking mode. DeepSeek: R1 series. Most consumer apps now let you toggle between fast and thinking modes — Claude's "Extended Thinking" button is the clearest UX.
Related reading
Bottom line
Reasoning models are the right tool when you have a hard problem and 30 seconds to spare. They are the wrong tool for quick everyday tasks. Knowing when to switch is one of the biggest skills in using modern AI well.
