OpenAI has published a practical guide for startups building with its GPT-5 model series. GPT-5 is described as its most powerful and most steerable model yet, built for coding and agentic tasks, and it reaches 74.9% on SWE-bench Verified. The company notes that prompts written for GPT-4.1 or other models won't always transfer directly, so developers will need to refine prompts to match GPT-5's behavior and personality.
The guide covers four areas: migrating to the Responses API, optimizing prompting, steering how the model reasons and communicates, and troubleshooting common pitfalls such as overthinking or overly verbose answers. OpenAI says the Responses API is essential because it lets the model persist its chains of thought across turns and tool calls, improving performance and cache-hit rates while lowering costs. Chat Completions does not support this capability.
According to the guide, the Responses API also reduces orchestration glue code, supports zero-data retention compatibility, and is the path forward for new reasoning features. OpenAI recommends that startups move their workflows to it now.
GPT-5 is positioned for complex multi-step reasoning, tool orchestration, structured outputs and business process automation, where higher accuracy and more predictable behavior are the stated goals. The guide draws on OpenAI's work with startups that have strong technical resources.
Source: OpenAI Blog · Summarized by HeadlinesBriefing