Understanding the cost of GET requests from AWS Lambda to AWS S3 in the same region

Hi, your understanding is correct that you will not be charged for data transfer, if it is within the same region. Per the pricing page:

You pay for all bandwidth into and out of Amazon S3, except for the following:

• Data transferred out to the internet for the first 100GB per month, aggregated across all AWS Services and Regions (except China and GovCloud)
• Data transferred in from the internet.
• Data transferred between S3 buckets in the same AWS Region.
• Data transferred from an Amazon S3 bucket to any AWS service(s) within the same AWS Region as the S3 bucket (including to a different account in the same AWS Region).
• Data transferred out to Amazon CloudFront (CloudFront).

However, you will be charged for the requests you make to the bucket. The cost per request depends on the storage class, the type of request, and the region. You can see the details in the "Storage & requests" tab on the pricing page, under the "Requests & data retrievals" section. For example, in us-east-1, the price is $0.0004 per 1000 GET requests on the S3 standard storage tier.