Back of the envelope guesses for my own satisfaction:

">$100MM yearly" is, let's say, $8.5MM monthly.

">10,000 customers" is <15,000 (or they would have used that), so maybe 11,000 to 13,000.

That's around $650-$750 per customer per month.

"Hundreds of thousands of active users" means maybe 250,000-400,000.

That's 20-35 users per customer, when split between 11,000-13,000 customers.

That comes out to $21-$34 per user per customer per month, average (you can see pricing tiers here: https://www.pagerduty.com/pricing/).

(I don't know if they make money off contracts not available on their pricing page.)