GPT-5.5: Fast, Brilliant, and Slightly Unhinged
Why GPT-5.5 became one of my favourite coding models despite its unpredictability and terrible first attempts at front-end design.
GPT-5.5 remains one of my favourite models I have worked with.
It was the first reasoning model that made speed feel like a feature rather than a compromise. Instead of spending twenty minutes thinking about the task, it could spend a few seconds reasoning and then start implementing.
That changed my workflow.
Efficient Reasoning
I do not normally want a model sitting on XHigh or Ultra for every task. Most of my work is better served by Low or Medium reasoning, a clear plan, and a fast implementation loop.
GPT-5.5 understood that style of work. You could explain what you wanted, and it would normally get moving without turning the conversation into an interview.
When it was good, it was astonishingly good. It understood the goal, implemented quickly, and gave you the feeling that the entire codebase was moving at once.
The problem was consistency.
Sometimes 5.5 behaved brilliantly. Sometimes it behaved like a maniac. You could never be completely certain which version had arrived for the session.
Great Starts, Weak Finishes
GPT-5.5 could implement most of a plan extremely well, then become strangely lazy near the end. The broad architecture would be there, the important files would be changed, and the last ten percent would quietly turn into placeholders, missed states, or details it claimed were complete.
That meant I had to keep checking the actual result. A confident summary was not proof that the work was finished.
That is why I still treat GPT-5.5 as brilliant but supervised. It can move incredibly quickly, but the last stretch needs checking.
Front-End Design Was the Weak Point
GPT-5.5 had about as much natural front-end taste as a toddler with a box of crayons.
Without a visual reference, the interfaces could be horrific. Generic gradients, strange spacing, too many cards, and design decisions no human had requested.
There was one reliable trick: give it a screenshot of the intended design. Once it had something concrete to follow, it became far more capable. The problem was never that it could not write CSS. The problem was that it could not consistently decide what good CSS should produce.
That weakness does not erase what made GPT-5.5 useful. It just means I trusted its speed more than its taste.
A Warmer OpenAI Model
GPT-5.4 often felt determined to reject whatever you proposed. GPT-5.5 softened that personality and became much more pleasant to work with.
It would still challenge ideas, which I value, but it felt warmer and more collaborative. That balance is one of the reasons I stayed with it even when newer alternatives appeared.
The Verdict
I rate GPT-5.5 7.9 out of 10.
GPT-5.5 was fast, understandable, occasionally brilliant, and occasionally completely unhinged.
It taught me how valuable efficient reasoning could be. It also taught me never to trust an agent's completion message without checking the final interface.
That is enough for it to keep a strong place in my rankings. It made fast, agent-led development feel genuinely fun.