Hi
@AlisonBaxter it's likely to be so individual from what I have gleaned, and trust me, I have read so much to get an answer, as I am currently honeymooning without insulin, and live in fear of the day that all changes.
I was told that if/when I start waking constantly over 6, and staying above 8 for extended periods after eating, it will be time to start insulin, and the honeymoon will be ending.
I eat low carb, (100g/day, c.25g per meal plus a couple of nut snacks), and exercise daily - so although my diet is restricted it is not identical each day, but my Libre helps keep me in check and see where I have gone over night and the real spikes etc.
If I ate a 'normal' carb-filled diet I am sure I would need to be on insulin to get my levels down, and be stressing my pancreas into quick submission. As I'm not a 'foodie' I am happy to 'go without' and prolong my time without insulin in any way I can, including reducing as much stress as possible, (spikes me more than a bag of jelly babies, probably!), and following @glucosegoddess on instagram's hacks (Jessie Inchauspé).
From my own experience I would say the honeymoon will be over when insulin is needed and small amounts don't bring on a hypo because my pancreas has stopped being 'helpful' - I tried for 3 weeks and on 3 units of humulin M3 twice a day I was dipping to the low 4s and treating with Quality Street (it was Christmas!) from being in the 20s at diagnosis aged 51, so I needed to come off it for my sanity.
After 12 months of low carb my HbA1c has kept reducing and my GAD antibodies have also decreased, and I will have my c-peptide re-checked in the summer, as I am bit of an anomaly.
I totally get the wanting to know and have 'proper' definitive answers, but after 16 months I am (happily?) resigned to the fact that with diabetes, there is no such thing.
Just seen you latest post - infections, illness, antibiotics, steroids (everything!) will increase most likely your BG, hopefully temporarily, so I would expect your insulin requirement to go back down a bit when you recover, but your diabetes team will be able to guide you on that.