Hello, I’m not quite sure it’s been pointed out adequately yet or if the Google team are aware, but it seems that the public GA Gemini 2.5 which I assume is 06-05 hallucinates considerably more that it’s predecessor 05-06. I do a lot of programming and I use Gemini to assist me and the current GA will often not understand my instructions, forget core coding practices or flat out not able to rectify its own code. Compared to 05-06 which was very prolific at coding and sticking to instruction with almost zero hallucination.
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We see the complete opposite in our tests. 05-06 was a horrific downgrade after the incredible 03-25. 06-05 bought a lot of that magic back again re: coding specifically and fixed a lot of the problems the previous model had.
ymmv of course, but it’s not a blanket statement
If you want the Gemini team to actually investigate, they would need prompts + responses that demonstrate issue clearly to act upon. Otherwise it’s kinda like shouting into the wind I’m afraid.
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Hello,
Welcome to the Forum!!
Could you please share any details about scenarios when you are facing this issue?
One possible solution to hallucinations can be prompting engineering, one can try to fine-tune prompt to be precise, clear and avoid ambiguity.
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Thank you for your comment, it inspired me to write a bug report to explain my recent experience. Sad I was on a break from development to not test the 03-25.
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Interesting. I’ve been using Gemini to learn about abstract algebra, and the hierarchy for me is clear: 03-25 > 05-06 > 06-05 > whatever is going on now.
Has the 05-06 version of 2.5 Pro been retired or pulled from availability? Although my API calls are directed to the 05-06 version, I’ve noticed a significant degradation in performance that makes it indistinguishable from the current official 2.5 Pro release. The performance of this current 2.5 Pro version is notably poor. I strongly suspect that the 05-06 version has been silently deprecated and its requests are now being rerouted to the official 2.5 Pro. If the original performance characteristics cannot be restored, I will unfortunately have to discontinue my use of Gemini, as it no longer fulfills my operational needs.
Yeah I’m pretty sure this is what’s happening - 05-06 is no longer available on AI studio. In the past when models got retired that way, it meant that requests toward them would be redirected to the version replacing them (gemini-2.5-pro in this case).
I don’t have prompts to share. I don’t keep prompt history in entirety, I apologise. I described the issue the best I could though. Gemini 2.5 has been rendered useless to me since this post and I haven’t considered using it until it returns to its prior strength.
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I agree, Gemini made significant leaps forward about 2 months ago, and now for some reason seems to have taken many steps back.