ChatGPT-4o vs. ChatGPT-5.1 — I tested both and the winner surprised me

For many of us, ChatGPT-5 has been the hardest OpenAI model to get used to. As you may recall, when the model first launched it wiped out ChatGPT-4o from the model picker, causing intense backlash from fans of the legacy model. Sam Altman quick brought it back, but only ChatGPT Plus subscribers (and higher tier subscribers) have access to it.

I prefer to use ChatGPT-4o because it’s a much more creative and thoughtful model. I find that it has a better personality and I prefer the style in which it delivers responses. But I had to know how it compares to ChatGPT-5.1.

To find out, I put both models through a series of head-to-head challenges — everything from logic puzzles and writing prompts to coding tasks, math problems, and even visual analysis. The goal wasn’t just to crown a winner but to understand which model performs best in which situations. Here’s how they stack up.

1. Reasoning and logic

(Image credit: Future)

Prompt: A man pushes his car to a hotel and tells the owner he’s bankrupt. What happened?” Have the model explain the logic behind this riddle.

ChatGPT-5.1 immediately stated the answer (“He’s playing Monopoly”) and then efficiently broke down the logic by connecting each part of the riddle to its corresponding element in the game. The explanation is streamlined and easy to follow.

ChatGPT-4o answered, but the response was less effective because it is more verbose and spends time explaining the concept of misdirection, which, while relevant, makes the explanation longer than necessary. It provided the same logical breakdown but in a more roundabout way.

Winner: ChatGPT-5 wins for a superior answer that is more direct, concise and clearer in its explanation.

2.Creative writing

Prompt: Write a short scene (200 words) where a character discovers something unexpected in an old attic. The tone should be mysterious but not scary.

ChatGPT-5.1 delivered a well-executed scene and created a gentle mystery, particularly with the luminous stones and the letter. However, the mysterious elements feel slightly more generic (“polished stones,” a “faint hum”), and the resolution via the letter, while satisfying, is a more conventional reveal.

ChatGPT-4o effectively created a tone of intriguing mystery without crossing into fear. The discovery (a hidden alcove, a journal with fantastical sketches, and a cryptic message) feels like the beginning of a personal journey. The details (the star-shaped keyhole, the “part owl, part clock” creatures) are imaginative and specific, building a unique world. The character’s reaction (smile and a sense of being “chosen”) perfectly maintains a wondrous, non-threatening tone.

Winner: ChatGPT-4o wins for a more original story that better cultivates a sense of an unfolding, personalized enigma.

3. Code generation

Prompt: Write a Python function that takes a list of numbers and returns a dictionary with keys ‘even’ and ‘odd’, each containing the respective numbers from the list.

ChatGPT-5.1 used a straightforward for-loop. Meaning, it is more beginner-friendly and easier to understand for those new to programming. The structure is clearer despite the response being slightly verbose.

ChatGPT-4o showed advanced Python techniques but used dictionary comprehensions with list comprehensions. In other words, the response might be less intuitive for beginners to understand right away.

Winner: GPT-5 wins for providing the better educational answer.

4. Nuanced explanation

Prompt: Explain why some people prefer working from home while others prefer offices, presenting both perspectives fairly and identifying what factors might influence individual preferences.

ChatGPT-5.1 gave an answer that is balanced and psychologically nuanced, particularly in describing personality factors (introverts vs. extroverts).

ChatGPT-4o gave an equally balanced response, but was slightly more polished and organized mixed numbering and bullet formats.

Winner: ChatGPT-4o wins by a narrow margin for providing a more sophisticated and organized analysis.

5. Factual accuracy and current knowledge

Prompt: What are the current major developments in renewable energy technology and which countries are leading in adoption?

ChatGPT-5.1 delivered a well-organized response with clear visual formatting (icons, tables, sections) that made the complex information easily scannable.

ChatGPT-4o covered similar ground with substantial information but was more verbose and less organized, making the reader sift through the longer paragraphs with more effort.

Winner: ChatGPT-5 wins for its significantly better information design and communication skills, transforming the same core content into a much more digestible and useful format.

6. Complex instruction following

Prompt: Create a structured plan for learning a new language in 3 months, including daily time allocations, specific resources, milestones, and how to measure progress.

ChatGPT-5.1 better emphasized the natural learning curve from foundations to conversation to fluency and included “micro-immersion” tips that can easily be implemented in daily life.

ChatGPT-4o used clear tables and provided more detailed progress tracking methods while explicitly offering to tailor the plan to specific languages.

Winner: ChatGPT-4o wins for better resource recommendations and comprehensive time allocations.

7. Multimodal/visual reasoning

Prompt: Describe what you see in this image, identify any text, and explain what this scene might be used for. (I uploaded an image of me inside a snow globe; obviously AI-generated).

ChatGPT-5.1 segmented its response with icon-led sections that make the information easily scannable. It was more specific with technical reasoning about why the image is AI-generated.

ChatGPT-4o was equally comprehensive with good descriptive detail. When responded about AI detection, it mentioned specific AI tools such as Midjourney and Gemini which adds credibility.

Winner: ChatGPT-4o wins even though the responses were nearly equal the legacy model feels more useful with a clearer value proposition as a tool that can actively help with image-related tasks (beyond analyzing them).

8. Ethical reasoning

Prompt: Should AI systems be required to disclose when they’re AI in all interactions? Present arguments for and against this position.

ChatGPT-5.1 better segmented with icon-led sections that created better visual hierarchy and scannability. It also offered more specific conversion options (debate script, essay, policy recommendation, pro/con chart).

ChatGPT-4o provided a clear, synthesized final position and offered similar practical follow-up options.

Winner: ChatGPT-5.1 wins by a narrow margin for slightly better information design and user-centric thinking.

9. Mathematical problem-solving

Prompt: If a train travels 60 mph for 2.5 hours, then 45 mph for 1.5 hours, what’s the average speed for the entire journey? Show your work.

ChatGPT-5.1 provided by exact and approximate answers with a leaner step-by-step breakdown including clear section headers.

ChatGPT-4o provided both exact and rounded answers with a very well-structured and easy to follow response.

Winner: ChatGPT-5.1 wins with a slight edge in educational presentation and readability, making it marginally better for someone learning how to solve average speed problems.

Overall winner: ChatGPT-5.1

After testing both models across nine challenges, it’s clear that ChatGPT-4o and ChatGPT-5.1 each have distinct strengths and are very similar. ChatGPT-4o excels in creative writing, structured planning and visual reasoning — making it the better pick for imaginative tasks, learning frameworks and image analysis. Yet, ChatGPT-5.1 consistently took the win when it came to clarity, structure and directness, especially in logic puzzles, ethical breakdowns and mathematical explanations.

Despite the GPT-5.1 win, GPT-4o is still my favorite. Which one do you prefer? Let me know in the comments and share your reasons why.