Basically I scrolled through their mastodon site and saved relevant posts.

But first, the general range of OEMs:

We're working with a major Android OEM. It's one of the top 10 Android OEMs by sales. It's a definitely company you know already. They're hard at work on developing GrapheneOS support for one of their upcoming 2026 devices but it won't be possible to meet the requirements until the next generation, likely in 2027. Snapdragon Elite 8 Gen 5 is currently the only SoC meeting our requirements for non-Pixel devices but that doesn't mean any device using it meets our requirements at all.

https://mastodon.social/@GrapheneOS@grapheneos.social/115877675057484385

From IDC https://www.idc.com and Phone area https://www.phonearena.com I have:

Samsung
Apple
Xiaomi
Transsion
Vivo
Oppo
Honor
Motorola
Realme
Huawei

It's still to be answered which of those companies are selling phones with the Snapdragon Elite 8 Gen 5.

Here are posts:

We're working with an OEM towards at least one other device meeting our hardware security and update requirements which should launch in 2026 or 2027. For now, Pixels are the only devices meeting the requirements listed at https://grapheneos.org/faq#future-devices so we can't provide the protections we do on other devices.

Samsung devices either don't allow an alternate OS or cripple functionality with one.

https://mastodon.social/@GrapheneOS@grapheneos.social/115511365721507644

It seems unlikely that it's Samsung.

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The next two seem to be unnecessary but people still keep bringing them up.

Here is a post of it not being fairphone:

Fairphone is not a major Android OEM and not the company we're working with on this.

https://mastodon.social/@GrapheneOS@grapheneos.social/115547303172412893

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It's not a European OEM and there aren't any open hardware options.

https://mastodon.social/@GrapheneOS@grapheneos.social/115335283516216137

So, it's also not Nothing.

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This reduces the list to:

Xiaomi (unlikely; I heard you have to apply for unlocking the bootloader, restrictive)
Transsion (Africa/India, low- and mid-range models)
Vivo (Snapdragon but locked bootloader)
Oppo (Snapdragon, but restrictive)
Honor (Snapdragon, but also restrictive)
Motorola (more likely, as others have pointed out, has allowed bootloader unlocking)
Realme (Snapdragon, but locked bootloader)
Huawei (doesn't use Snapdragon due to US sanctions)

With that, it looks like it'll be Motorola.

But Motorola has not confirmed a device equipped with the Snapdragon Elite 8 Gen 5 yet. In another post (https://mastodon.social/) GrapheneOS mentions:

We're partnered with a major Android OEM and they're actively working on supporting GrapheneOS for devices in 2027 by meeting all of our update and security requirements. They weren't able to do it for the upcoming devices because Qualcomm didn't get hardware memory tagging working properly on every variant of their latest SoC generation that's in the process of launching. The upper level cache had to be changed to support MTE and they didn't do it for each SoC variant yet.

It sounds like the 2026 generation is already shipping with the Snapdragon Elite 8 Gen 5, only not having memory tagging working properly. That makes one of the chinese companies more likely (btw. motorola is also like 80% chinese, owned 100% by Lenovo but still some international workforce).

It's still the most likely to be Motorola I think.