1M context is amazing, but even after 100k tokens Gemini 2.5 Pro is usually incapable of consistently reproducing 300 LOC file without changing something in process. And it actually take a lot of effort to make sure it do not touch files it not suppose to.

With Gemini I have found some weird issues with code gen that are presumably temperature related. Sometimes it will emit large block of code with a single underscore where it should be a dash or some similar very close match that would make sense as a global decision but is triggered for only that one instance.

like code containing the same identifier.

    add_value(thing,other_thing)
    add_value(thing,other_thing) 
    add_value(thing,other_thing) 
    add_value(thing,other_thing)
    add-value(thing,other_thing)
    add_value(thing,other_thing) 
    add_value(thing,other_thing) 

Not to mention sneakily functions back in after being told to remove them because they are defined elsewhere. Had a spell where it was reliably a two prompt process for any change, 1) do the actual thing, 2) remove A,B and C which you have reintroduced again.

I have had some very weird issues with Gemini 2.5 Pro where during a longer session it eventually becomes completely confused and starts giving me the response to the previous prompt instead of the current one. I absolutely would not trust it to handle larger amounts of data or information correctly.

Exactly, 1M context tokens is marketing, relatively little training was done at that input size.