OnePlus, the Android-using smartphone manufacturer that recently announced closer ties with its parent company, OPPO, has also committed to three 'Oxygen OS' updates and 4 years of security updates for most of its range, see the details below. In fact, it's good to see most major phone makers doing likewise these days - phones are certainly usable longer.

From OnePlus announcement:

Six years ago, we created OxygenOS based on the idea that fast and smooth software is fundamental for a good smartphone experience. Since then, OxygenOS has proven to be one of the best Android operating systems available on the global market...

After a lot of evaluation and discussion, we’ve come up with a solid plan to best leverage our shared resources with OPPO. In order to improve efficiency and standardize the software experience across our portfolio, we’re working on integrating the codebase of OxygenOS and ColorOS. This is a change that you will likely not even notice since it’s happening behind the scenes. We now have a larger and even more capable team of developers, more advanced R&D resources, and a more streamlined development process all coming together to improve the OxygenOS experience.

OxygenOS remains the OS for global OnePlus users as always, but now built on a more stable and stronger platform. This will apply to new devices in the future, while for existing devices that are still within the maintenance schedule, it will occur via an OTA update along with Android 12. Most importantly, with this change, we are happy to announce an improved software maintenance schedule for the lifecycle of our open market smartphones:

• Flagship product line (including T / R): The OnePlus 8 series and newer devices will receive 3 major Android updates and 4 years of security updates.
• Nord / Nord CE: The first OnePlus Nord and newer Nord / Nord CE devices will receive 2 major Android updates and 3 years of security updates.
• Nord N series: Starting from N10 and N100, all N series devices will receive 1 major Android update and 3 years of security updates.

Although it's always worrying when companies 'plan to leverage their shared resources', since merging teams of developers and their codebases is always messy, I do wish OnePlus well. Promising four years of software support is the gold standard, I contend. A typical smartphone will be used by its primary owner for about two years, then another two years on the second hand market or with a family member, so all of this use will be covered against vulnerabilities.

By way of comparison, I also dug down into some competing timescales and promises:

• Samsung - also promised four years of security updates, with two or three major versions, depending on device
• Xiaomi - promises between two and four years of skin and security updates, depending on device
• Sony - promises two years of updates, with a rumoured three years for 'premium' devices
• Apple - promises between six and seven years of updates, depending on device
• Google - promises three years of updates, with a rumoured five for the Pixel 6 series onwards
• Fairphone - promises five years(+) of updates, including at least one major version

These are some of the better options, of course. There are plenty of lesser brands, or lesser (budget) models from big brands, which get less updates because it's not economically feasible to support them. 

For decent smartphones that would be considered by anyone discerning (and a reader here!), I consider three years of updates to be a minimum, four to be ideal, and five or more to be exemplary.