Customer.io vs Substack

as AI assistants see them, week of 2026-09-28

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Customer.io and Substack land close together overall, scoring 13 and 14 out of 100, with Customer.io named in 12 of 59 answers against Substack's 11 of 59. They split head-to-head evenly too: each comes out ahead on 5 questions, with 10 ties. The two serve different crowds in AI answers, though. Customer.io sweeps "best tool for automated onboarding and drip emails" and "best email platform that segments users by behaviour," both 3 of 3, while Substack sweeps "best newsletter platform," also 3 of 3. Claude rates Substack highest of the three assistants at 26, while ChatGPT and Perplexity favor Customer.io slightly more.

Head to head

metric	Customer.io	Substack
score	13	14
questions won	7	7

By assistant

Customer.io

assistant	score	named in, this week	usual spot, this week
ChatGPT	10	11% of answers	#1.5
Claude	19	35% of answers	#6.9
Gemini	not sampled this week
Perplexity	14	15% of answers	#1.7

Substack

assistant	score	named in, this week	usual spot, this week
ChatGPT	9	11% of answers	#2.5
Claude	26	35% of answers	#3.4
Gemini	not sampled this week
Perplexity	8	10% of answers	#3.0

Where they differ

Only Customer.io gets named for

What's the best tool for automated onboarding and drip emails?
What's the best email platform that segments users by behaviour?
What's the best email platform for a SaaS startup?
Which email tool has the best deliverability?
What's the best alternative to Mailchimp?

Only Substack gets named for

What's the best newsletter platform?
What's the best email tool for selling a paid newsletter?
What's the best email tool for a newsletter with sponsors and ads?
Which email platform is best for a solo creator?
What are the best free email marketing tools?

More comparisons

Not sold on either?

Scores count how often each assistant names a product, weighted by position. How the score works · Full Email marketing platforms leaderboard