OpenAI's deprecations table states it without decoration:
2026-09-28 · gpt-3.5-turbo-instruct → gpt-5.6-terra
On September 28, 2026, gpt-3.5-turbo-instruct shuts down. OpenAI names gpt-5.6-terra as the replacement. And it does not go alone: the same date takes babbage-002, davinci-002 and gpt-3.5-turbo-1106 with it.
Why this still catches people in 2026
gpt-3.5-turbo-instruct is a completions model, the older format. A lot of small automation — a message classifier, a field extractor, a short-summary generator — was built on it years ago. It works, it is cheap, and nobody touches it. That is exactly the kind of integration nobody remembers exists until it stops answering.
The honest caveat
Swapping is not just changing the model name in the call. gpt-5.6-terra uses modern chat and reasoning structure, with response mechanics that differ from the legacy completions endpoint. A prompt that leaned on the old behaviour may need reworking — and September 29 is the wrong morning to find that out.
The two-minute check
Search your codebase, or ask whoever built it, for the string gpt-3.5-turbo-instruct. If it shows up, that integration has a date on it. Search for babbage-002, davinci-002 and gpt-3.5-turbo-1106 while you are in there — same deadline.
Next date
September 28, 2026 — shutdown.
Source
OpenAI — Deprecations, developers.openai.com/api/docs/deprecations.
One honest note: there is no universal multiplier. The outcome depends on your industry, your ticket, and how much of your volume is urgent versus price-shopping. Anyone promising a fixed return is selling, not calculating.