Don't you mean the other way round? You always want to be running the most recent 2.6 servers, but when someone sends version 2.5 requests you transform the 2.5 to 2.6 and pass it along to your server (and vice Verda with responses)
The problem I guess is breaking changes come easily - it's fine if say we have example.com/homeaddress and now I add a zip code field in 2.6 - but a 2.5 request has no zip code and if 2.6 makes that mandatory it's really 3.0 - that just feels wrong. But it's a breaking change so, ok. But you get a deeper discussion then over why make a lack of zip code a breaking chnage ? Interesting
This kind of implies always have 2.5 running as front end code. I would rather have my latest code running (especially as it implies 2.4,2.3,,,1.3) and have that spin up the 2.5 munger code as needed. But yes I think it's more or less the same thing
Interestingly looking at stripe changelog https://stripe.com/docs/upgrades#api-changelog they still do breaking code changes every month or two so despite the effort and with a smallish api they break a lot of contracts.
The odd thing is that they keep a different api version for each customer, tagged at customers settings, so I suspect your approach (spin up api based on incoming version) might work better - but boy I think they may be in a lot of pain trying to maintain that backwards compatibility
The problem I guess is breaking changes come easily - it's fine if say we have example.com/homeaddress and now I add a zip code field in 2.6 - but a 2.5 request has no zip code and if 2.6 makes that mandatory it's really 3.0 - that just feels wrong. But it's a breaking change so, ok. But you get a deeper discussion then over why make a lack of zip code a breaking chnage ? Interesting