GPT-5 launched August 7, 2025. By March 2026, the current version is GPT-5.1. Here's what it actually does differently from GPT-4, and what it means for developers and businesses building with AI.
What Actually Changed
OpenAI's official description: GPT-5 "produces high-quality code, generates front-end UI with minimal prompting, and shows improvements to personality, steerability, and executing long chains of tool calls."
That's marketing language. Here's what that means in practice:
- Coding: GPT-5 is now the top coding model on SWE-bench Verified, beating Claude Opus 4.6 in actual software engineering tasks. It can write, debug, and refactor production code with fewer errors.
- UI generation: It can take a rough text description and produce functioning React components or HTML/CSS. Not production-ready code, but a solid starting point.
- Tool use: The "long chains of tool calls" improvement means agents built on GPT-5 can reliably execute multi-step workflows — book flights, run code, query databases, send emails — without losing track of context.
- Personality/steerability: You can now have extended conversations where the model maintains a consistent character, memory, and approach across sessions.
The Price Drop That Matters More Than the Model
The most practically significant change: GPT-5 inference costs dropped approximately 73% compared to GPT-4 at launch. Input tokens: roughly $2.50 per million. Output tokens: roughly $10 per million.
For developers, this is transformative. Applications that were economically marginal at GPT-4 prices become straightforwardly profitable at GPT-5 prices. The price of AI inference has dropped roughly 99% in five years. That trajectory hasn't slowed.
GPT-5 Pro: The High-End Tier
OpenAI also released GPT-5 Pro, replacing o3-pro. The Pro variant "thinks for ever longer, using scaled but efficient parallel test-time compute, to provide the highest quality and most comprehensive answers."
Translation: for the hardest problems, GPT-5 Pro uses significantly more compute to think through problems more thoroughly before answering. It's OpenAI's answer to Claude Opus 4.6's strong performance on reasoning benchmarks.
What This Means for Application Builders
The practical advice hasn't changed: build with the model that gives your application the best capability-to-cost ratio. GPT-5 is currently the best model for many tasks, but Claude 4 is competitive on reasoning, and both are improving fast.
Build your application so you can switch models as the landscape evolves. The model that's "the best" changes every few months. The company that gets locked into one provider because of short-term convenience usually pays for it later.
The Honest Assessment
GPT-5 is a genuine step forward. The coding improvements alone justify the upgrade for any developer team. But the jump from GPT-4 to GPT-5 is smaller than the jump from GPT-3 to GPT-4. The low-hanging fruit of AI capability improvement is getting harder to reach.
What hasn't changed: the need for human judgment about where and how to use these tools. The model is only as good as the workflow it's embedded in.
