The Open GApps project provides a convenient way to get up-to-date Google App packages (most often used in combination with custom ROMs). Unfortunately they do not always offer the most recent versions and it takes some time until new Android releases are reflected on the official Open GApps project website. As of this writing, Android 8.1 is the most recent Android version and is not yet in the portfolio of the Open GApps project.

Fortunately they publish their automation and all necessary assets on GitHub. Therefore building your package from their sources is pretty feasible. The following guide is done for macOS, but should be quite similar to most Linux distributions (hint: you can use the beevelop/android Docker image to save some time):

# Install lzip via brew (Open GApps depends on it)
brew install lzip
# Clone the main repository
git clone git@github.com:opengapps/opengapps.git
# Download the sources for your targeted architecture (arm64 in my case)
# Downloading and „uncompacting“ the repositories takes quite some time
# Get a coffee or two in the meantime
./download_sources.sh --shallow arm64

# The final step is building the package itself
# This also does take quite some time
# especially depending on your CPU power (due to compression stuff, etc.)
make arm64-27-stock

The following script might help you getting started by using the Docker image mentioned above. Just run the following commands inside the Docker container (e.g. docker run -it --rm beevelop/android):

apt install build-essential lzip git zip
# SSH-Key on the machine is required and has to be added to your GitHub account
git clone git@github.com:opengapps/opengapps.git
./download_sources.sh --shallow arm64
make arm64-27-stock
# The command should great you with:
# SUCCESS: Built Open GApps variation stock with API 27 level for arm64 as [...path...]

Afterwards you can transfer the resulting zip file from Docker container to your host machine using docker cp:

docker cp practical_wilson:/root/opengapps/out/open_gapps-arm64-8.1-stock-20180203-UNOFFICIAL.zip .
# from there on scp it to your local computer and put it on your gorgeous mobile phone