Hi Siqi Yang,
Here is the latest update related to MS Graph API pricing.
https://devblogs.microsoft.com/microsoft365dev/microsoft-graph-data-connect-pricing-updates-2/
The first 100K basic objects accessed per tenant per billing period will not be charged (estimated at $75 per billing period). Basic objects are defined as datasets generated from raw customer created content and inputs from Microsoft 365 applications and services.
So for your case, Outlook events endpoint is consider the basic objects and you can follow the pricing model as per the guideline.
Just for additional information, as for MS Team API, the pricing is bit different.
https://learn.microsoft.com/en-us/graph/teams-licenses
Hope this helps.
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