Did gemini-3.1-pro-preview change in July 2026? Our results got less consistent

Our question

Does gemini-3.1-pro-preview always use the same model, or can Google swap it for a
newer one without changing the name? If it was swapped between 6 July 2026 and
6 August 2026, please let us know. And is there a model name we can use that never
changes?

What we do

We send 33 short audio clips (about 1 second each, Opus, 48 kHz, mono) plus a text
prompt in one generateContent request. The model sends back a table with one row
per clip. Each row has a category and a score from 0 to 100.

Our settings have not changed since 15 April 2026:

“generationConfig”: {
“temperature”: 0.0,
“maxOutputTokens”: 64000,
“thinkingConfig”: { “thinkingBudget”: 40000 }
}

Over the last few days, the same kind of audio has been getting less consistent
answers than before.

What would help us

  1. Do names ending in -preview always point to the same model, or can they change?
  2. If they can change, did gemini-3.1-pro-preview change in July 2026?