You compressed images, set up a cache, went through the plugins, and your site still does not feel as fast as it should. There is a factor rarely mentioned in speed guides that has nothing to do with any of that: the version of the protocol the server uses to communicate with each visitor's browser.
What HTTP is, in plain terms
Every time a browser asks for a page, an image or a stylesheet, it does so following a protocol called HTTP: a set of rules defining how those resources are requested and delivered. For decades there was one widely used version. Then came two updates, HTTP/2 and HTTP/3, which do not change what gets requested, but how that information travels between server and browser.
The problem HTTP/2 solved
With the old version of the protocol, the browser had to open a separate connection for every single resource it needed, and wait its turn if too many were already open at once. A page with many images, stylesheets and scripts ended up generating dozens of those connections, each with its own startup cost.
HTTP/2 lets all those resources travel mixed together inside a single connection, instead of opening a new one for each. The most noticeable result is that pages with many files, which is the vast majority of real sites once you count images, styles and scripts, load faster, without changing a single line of the site itself. The improvement lives entirely in how the information is transported.
What HTTP/3 brings
HTTP/3 goes a step further and also changes the underlying transport technology responsible for making sure data arrives complete and in order. The advantage shows up especially on unstable connections: mobile networks with variable signal, or wifi with interference. With the older transport technology, a single lost data packet could stall delivery of everything else until it was resent; with what HTTP/3 uses, one stuck resource does not block the others that arrived fine.
For a visitor on a good broadband connection, the difference between HTTP/2 and HTTP/3 is hard to notice. For one on an unstable connection, very common on mobile, a steadier load can genuinely be felt.
How to check which version your site uses
No configuration change is needed to find out: any modern browser shows it in its developer tools, in the network tab, as a column indicating the protocol used for each resource loaded. There, resource by resource, you can see whether it travelled over the new version or the old one.
Today it is standard for the web server to automatically offer the newest version each visitor's browser is able to understand, with no special action from the site. That is why, if your hosting runs on updated server software, you are probably already using the newest version without having configured it on purpose.
What it does NOT fix, and it needs saying
This matters so expectations stay realistic. A newer transport protocol does not compress a heavy image, does not fix a badly written plugin, does not reduce unnecessary database queries, and does not replace a cache. It improves how data travels, not how much data there is to send or how efficient the code generating it is.
A site with several-megabyte uncompressed photos is still slow over HTTP/3, exactly as it was over the old version. The protocol upgrade helps, but it is one factor among several, and not the biggest one: image weight and code efficiency remain what weighs most on the actual speed a visitor experiences.
What is on you and what is on the host
Offering these protocol versions is the server's responsibility, not your site's. Hosting running modern server software enables it without you needing to ask. What is on you is everything else that makes up real speed: image weight, plugin count, whether a cache is configured, and how efficient your theme is.
So if your site is slow, checking the protocol makes sense as part of a full diagnosis, but it is not the first place to look. It is worth checking what you directly control first, which usually has a far bigger impact.
What if your hosting does not offer the newest version yet
If you check the browser tools and see your site is still using the older protocol version, that is not something you can change yourself from the panel: it depends on the server software your provider has installed. Most current hosts already offer it out of the box, so if yours does not, it is worth asking support whether an upgrade is planned, or whether it is already available and simply needs enabling on your account.
It is not a reason to switch hosts on its own: as explained above, the real impact on perceived speed is usually smaller than other factors you control directly, so those are worth prioritising before treating this as the main problem.
If you do decide to check, ask specifically rather than assuming: support can confirm in one message whether your account is already on the newest version, which saves you from guessing based on outdated articles about what a given provider used to offer.
Protocol support is also one of the details worth comparing when you are choosing a host in the first place, alongside more visible features like storage or included security. It costs nothing to ask before signing up, and it saves a conversation with support later.