How long it has been since the last release against the line's usual gap and its recent ones — the rhythm, not a date.
Newest first — what each version changed versus the one before, in OpenAI's own numbers.
OpenAI's new flagship: far fewer made-up answers and a third of the tokens on coding-agent work, but the same overall score as GPT-5.6 Sol — at 2.5 times the price.
Compared with GPT-5.6 Sol · the model it replaces
Invents facts on half as many trick questions
AA hallucination rate — how often it makes up an answer instead of admitting it doesn't know
51%
▲ down from 92% · 41 points fewer
Uses about a third of the tokens on coding-agent tasks
AA Coding Agent Index, max effort — text consumed per task
~⅓ tokens
▲ vs GPT-5.6 Sol · 70% more token-efficient
Costs 2.5 times more to run than Sol
Price per 1M tokens — what developers pay, input / output
$10 / $50
up from $4 / $20 · 2.5× the price
OpenAI's GPT-5.5 roughly doubles its reasoning over very long documents and writes shorter answers than GPT-5.4 — but it costs twice as much to run.
Compared with GPT-5.4 · the model it replaces
Roughly doubles its reasoning over book-length documents
1M-token input — handling very long documents in one go
74.0%
▲ up from 36.6% · roughly doubled
Writes shorter answers to long prompts
Output length — how much text the model produces
19-34% shorter
▲ vs GPT-5.4 · same prompts
Costs developers twice as much to run
Price per 1M tokens — what developers pay, input / output
$5 / $30
price doubled — was $2.50 / $15
One email a week: what AI models shipped, the actual differences vs the previous version, and what's coming next. No filler.