I am advised that the Kabusa wire is without doubt the most flexible.
That stuff looks pretty good in terms of flexibility, but check out Audio Note AN-WIRE-300. It’s made from three strands of 0.0019" thick silver wire (half the thickness of the average human hair) and has 6 coats of polyurethane as insulation. It’s incredibly hard to work with, but I can’t imagine anything thinner or more flexible. I ran mine straight from the cartridge clips to phonostage RCAs.
https://www.hificollective.co.uk/wire/audio-note-silver-internal-tone-arm-wire.html
Here’s my wire next to a typical Bic ball point pen: