ChatGPT Reasoning Verified 19 Aug 2026

GPT-5.5 Thinking

OpenAI's previous deliberate reasoner for hard, multi-step problems.

Previous generation. Use GPT-5.6 Sol instead. Previous generation. GPT-5.6 shipped 9 Jul 2026.

Maker: OpenAI
Context: Large (see OpenAI docs)
Pricing: See OpenAI pricing / See OpenAI pricing

Not available on the free tier.

Best for

Multi-step analysis, trade-off reasoning, planning
Problems where a quick answer is usually wrong
Workflows you pinned before the 5.6 release

Prompting quirks

Don't tell it to "think step by step"

Reasoning models already do this internally. Step-by-step boilerplate adds tokens and can make output more verbose, not better. State the goal and the constraints instead.

Give it the success criteria, then get out of the way

"Optimise for X, here are the constraints, here's what done looks like" beats a long procedural script. Let it find the path.

Copy-paste example

Tuned for GPT-5.5 Thinking. Swap in your own content where marked.

Pressure-test a prioritisation

Here is our Q3 roadmap and the reasoning behind the ranking:
{paste roadmap + rationale}
Find the weakest link in this prioritisation. What are we assuming that,
if false, would flip the order? Give me the single highest-leverage
thing to validate first and why.

Facts verified against the official OpenAI docs on 19 August 2026.