Hi Dominik
Thanks for reaching out. We build Actions token size based on common practice and use case, centred around practice to ensure Actions performance and limit relevant latency. For now, we have keep the cumulative size of cached keys and their values must not exceed 8192 bytes.
If you have additional use case on increasing size, feel free to share with me.
At Auth0 Doc we provided examples on using Actions caching, and Actions editor also provide real time editing hit for using caching.