Joseph Keller, at iMore writes:

AgileBits has announced that they're upcoming iOS 8 extension for 1Password is now supported by over 100 apps. The updates for the apps supporting the extension, as well as 1Password itself, will be available when iOS 8 ships later this year. In the meantime, AgileBits has previewed twenty of the apps that will ship with support for the extension.

From AgileBits:

We can't share the full list of developers yet (we just cracked 100!). But we can show you nearly 20 apps that are already working on integrating 1Password's iOS 8 App Extension for fast, one-tap logging in and even updating your passwords!

Extensions are going to be huge.