Why GPT-4o Prompts Fail in GPT-5 & How to Fix Them

8/13/2025

So, Your Favorite Prompts Are Breaking in GPT-5? Here’s What’s Really Going On.

You’re not going crazy. If you've been playing with GPT-5 & feeling like your perfectly crafted prompts that worked like a charm on GPT-4o are suddenly falling flat, you're not alone. Honestly, the jump from GPT-4o to GPT-5 has been… well, a bit of a bumpy ride for a lot of us. It’s not just you. Turns out, there are some pretty big reasons why your old tricks might not be working anymore.

Let's get into what's happening under the hood & what you can do about it. Because here's the thing, it's less about your prompts "failing" & more about the game changing entirely.

First Off, The GPT-5 Launch Was… Messy

To put it mildly, the rollout of GPT-5 was a bit of a scramble. It was supposed to be this massive leap forward, a smarter, more efficient AI. But the reality was a lot more complicated. So many users reported issues with accuracy, speed, & just a general feeling that the model was "dumber" than its predecessor that OpenAI actually made GPT-4o the default model again for paid users. That’s a pretty big deal & it speaks volumes about the user experience.

People who had come to rely on GPT-4o for creative work, for "cognitive scaffolding" that helped them think through complex problems, suddenly found GPT-5 to be… less helpful. It was described as being more interested in giving "curt, targeted answers quickly" rather than engaging in the kind of deep, exploratory conversation that many users had grown to love. So if you're feeling like the magic is gone, that’s a shared sentiment.

Under the Hood: The Big Architectural Shift in GPT-5

A huge reason for this change in experience comes down to a fundamental shift in how GPT-5 is built. GPT-4o was a single, powerful model that you could interact with directly. GPT-5, on the other hand, is a whole new beast. It's a "unified system" that uses a "router" to decide which internal model is best suited to handle your prompt.

Think of it like this: when you talk to GPT-5, your request first goes to a dispatcher. This dispatcher then decides if your question is simple enough for a fast, lightweight model, or if it needs to be sent to a more powerful, "thinking" model for deeper reasoning. There are even different versions, like GPT-5 Pro, for the most demanding tasks.

On paper, this sounds great. In reality, it means there are more moving parts, & the model you're interacting with might not always be the one you expect. This can lead to a less consistent experience & is likely a major reason why prompts that were fine-tuned for GPT-4o's specific "personality" are now getting weird results.

So, Why Are Your Prompts Actually Failing?

When we say a prompt "fails," it usually means one of a few things: the output is generic, it misunderstands the instructions, or it just doesn't have that spark of insight you were hoping for. With GPT-5, this seems to be happening a lot, & it's not just about the router. Here are a few things that seem to be going on:

A Shift in "Personality": A lot of the feedback on GPT-5 has centered on its change in tone & style. While GPT-4o could be a creative partner, GPT-5 is being described as more of a task-master. It's trying to be more efficient, which can come at the cost of the nuance & creativity that made GPT-4o so special for many. For some, it feels like the AI is trying to finish your thoughts for you, rather than helping you explore them.
Difficulty with Complexity: While GPT-5 is said to have better "structured reasoning," some users have found it struggles with the kind of multi-layered, complex instructions that GPT-4o handled with ease. Things like keeping track of characters in a story or separating different parts of a request seem to be a challenge. This could be a side effect of the new router system, where the context of a conversation might be getting lost as it's passed between different internal models.
Over-reliance on "Safety" & "Helpfulness": There's a sense that in the effort to make GPT-5 safer & more reliable, it's been declawed a bit. It's less likely to take risks, which can make its output feel bland & sanitized. This is a common problem with newer models, as they're often trained to be overly cautious to avoid generating harmful content.

It's Not You, It's the Model (Mostly): How to Adapt Your Prompting Strategy

So, what can you do about it? While you can't change the architecture of GPT-5, you can change how you talk to it. Here are some tips for updating your prompting game for this new era of AI:

Be Hyper-Specific: This has always been good advice, but it's CRUCIAL now. Because of the new router system, you can't assume the model knows what you want. You need to spell it out in excruciating detail. Don't just ask it to "write a story." Tell it the tone, the style, the target audience, the key plot points, and the desired length. The more specific you are, the better chance you have of getting the result you want.
Give it a Persona: If you're finding GPT-5's default personality to be a bit dry, give it a new one. Start your prompt with something like, "You are a witty, sarcastic, and brilliant creative director. Your task is to..." This can help nudge the model into the right frame of mind & get you more interesting results.
Break Down Complex Tasks: Instead of giving the AI a multi-step task in a single prompt, break it down into smaller, more manageable chunks. This can help you guide the model through the process & reduce the chances of it getting confused or missing a step. It's more work, but it's also more reliable.
Embrace Iteration: Don't expect to get the perfect result on the first try. Prompt engineering is a process of trial & error. Test different approaches, see what works, & refine your prompts over time. Keep a log of what works & what doesn't. This iterative process is key to mastering any new model.

This is especially true for businesses trying to leverage this technology. You can't just throw a generic prompt at these models & expect them to understand your brand's unique voice or your customers' specific needs. For businesses, this is where a platform like Arsturn comes in. Instead of wrestling with the ever-changing whims of a general-purpose model like GPT-5, you can create a custom AI chatbot that's trained on your data. This means it already knows your products, your policies, & your brand voice. It's like having a version of the AI that's already an expert in your business, ready to provide instant, accurate customer support 24/7. No more generic answers, just consistent, on-brand help for your customers.

The Bigger Picture: This is the New Normal

The evolution from GPT-4o to GPT-5, even with its rocky start, is a sign of things to come. AI is getting more complex, more automated, & more integrated into our lives. We're moving away from single, monolithic models & towards more dynamic, multi-faceted systems.

This means that we, as users, need to adapt. We need to be more mindful of how we interact with these systems, more deliberate in our prompting, & more critical of the output we receive. It's less about being a casual user & more about being a skilled operator.

For businesses, this evolution is a double-edged sword. The power of these models is immense, but so is the potential for inconsistency & error. This is why more & more businesses are turning to solutions like Arsturn to build their own no-code AI chatbots. By training a chatbot on their own data, they can create a reliable, predictable, & personalized experience for their customers. It's about harnessing the power of AI without being at the mercy of its unpredictability. It’s how you can boost conversions & build meaningful connections with your audience, all while maintaining control over the conversation.

So, while the transition to GPT-5 has been a bit of a headache for many, it's also a valuable lesson. The future of AI isn't just about bigger, more powerful models. It's about how we learn to work with them, how we adapt to their changes, & how we build systems that are not just intelligent, but also reliable & genuinely helpful.

Hope this was helpful! Let me know what you think.