Every new workspace starts with a 14-day trial of the Pro plan, with full access to everything Pro includes. No card is needed to start.
During the trial
Settings > Billing shows how long is left ("Trial ends [date] · N days left"). You can subscribe at any point with Subscribe now: your card is not charged until the trial ends, and the plan tile tells you the exact date of the first charge. You can also switch plans during the trial; the change applies immediately, your trial carries on with the new plan, and the first charge still lands when the trial ends.
As the trial winds down
The workspace Owner gets a reminder email 3 days before the trial ends, and another email once it has ended.
What happens when it ends
If you have not subscribed by the end of the trial, your workspace moves to the Free plan rather than losing access. If your usage is above Free's limits, the extra members, knowledge bases, and articles are hidden rather than deleted, and come back when you upgrade. See The Free plan & plan limits for the details.
You can upgrade to a paid plan at any time, during the trial or afterwards.