Most prompt guides are maintenance manuals for models that no longer exist. This edition rebuilds the advice from the vendors’ current documentation, ranks the evidence, and flags the places where the three biggest labs contradict each other.
By Tom Morgan · First published April 12, 2026 · Fully revised September 30, 2026 · About 3,300 words · 14 min read
How this was produced. Research and drafting for this revision were AI-assisted. The vendor pages cited below were opened and read on September 30, 2026, not summarized from memory. No original benchmarks were run for this article, and nothing here should be read as a test result. Where a claim is my own analysis, it is labelled that way.
The short answer
Quick answer In September 2026, all three major vendors tell you to describe the outcome you want, supply the context the model cannot guess, state one or two hard boundaries, and stop there. They also tell you to delete instructions that were written for weaker models. They disagree on two things that matter: whether to include examples, and whether to script the steps. Treat any prompt you wrote before mid-2026 as legacy code and rebuild it from a smaller baseline instead of patching it.
Key facts at a glance
Fact Source type Date
OpenAI’s current family is GPT-6 (Astra, 6.1 Sol, Luna); its docs tell you to start from a fresh, minimal prompt when migrating Vendor documentation Read Sept 30, 2026
Anthropic staff said they cut about 80% of Claude Code’s system prompt because the newest models “want a smaller system prompt” Trade press reporting a conference talk July 2, 2026
Anthropic reports that putting the question after long documents improved response quality by up to 30% in its own tests Vendor documentation (first-party claim) Read Sept 30, 2026
OpenAI’s reusable “prompt objects” API is scheduled to shut down on November 30, 2026 Vendor documentation Read Sept 30, 2026
Google’s own Gemini prompting page recommends few-shot examples in every prompt Vendor documentation Page updated Sept 17, 2026
Why the April edition of this guide needed rebuilding
The first version of this article got the direction right (shorter, clearer, outcome-first) and several specifics wrong or stale. Rechecking it against current documentation turned up five problems:
It compared GPT-4o, o3, Claude 3.x and Gemini 1.5. None of those is the current generation. Google’s Firebase documentation notes that Gemini 2.0 Flash and Flash-Lite were scheduled to shut down on June 1, 2026.
It called role prompts dead. Anthropic’s current guide still recommends a one-sentence role. What has faded is the elaborate persona, not the role line.
It said pasted examples work best “across all models.” Google says so. An Anthropic staffer says the opposite for the newest Claude models. See the disagreement section below.
It said Anthropic recommends splitting tasks into sequential steps. Anthropic’s current guidance for its newest models leans toward handing over the whole task and the definition of done.
It contained a “sweet spot” chart (20–60 words) and an opening anecdote drawn from unpublished personal testing. That material couldn’t be documented or reproduced, so it has been removed. No vendor publishes a word-count target, and this edition doesn’t invent one. Read More...
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