SaaStr 842: The 90/10 Rule for AI Agents: What to Build vs Buy with SaaStr's CEO and CAIO
Summary
The episode centers on SaaStr's updated 90/10 rule for AI: buy 90% off-the-shelf and only build the 10% that delivers outsized, proprietary value. Hosts Amelia Lerutte (CAIO) and Jason Lemkin walk through real examples—an internal AI VP of Marketing and a sponsor/customer portal—showing how agent tooling like Claude Cowork made complex builds feasible and fast. They weigh the trade-offs of vibe-coding (rapid, low-code builds) versus buying SaaS, emphasizing hidden maintenance costs, security considerations, and the ongoing time sink for custom apps. The conversation stresses that AI is now table stakes: products without meaningful AI risk losing customers, while jaw-dropping AI experiences drive retention and growth.
Key Takeaways
- 1Apply the 90/10 rule: buy 90% off-the-shelf, build only the 10% that drives outsized value.
- 2New agent platforms dramatically accelerate building production-ready AI features.
- 3Hidden maintenance and people-time are the main long-term costs of custom vibe-coded apps.
- 4Zero AI in your product is a red flag—AI is now table stakes for differentiation.
- 5Measure real operational ROI by testing agents on concrete workflows first.
- 6Protect production-facing agents with regular security practices and clear guardrails.
Notable Quotes
"Is your jaw dropping? Almost every, if anyone that has even a couple million in revenue, up to billions, at some point your product was a jaw dropper or you never would have gotten there."
"These pre-built AI agents deploy in about 60 seconds and run for as low as two cents per successful action."
"If you feel like your app has zero AI, that's where I would be worried."
"It took Claude Cowork an hour (or a couple hours) to ingest contracts and create all the registration/promo codes — something that used to take us a day with a human."
""You have to get AI budget. You have to grow faster. That is what the world's saying.""
""Now hundreds and hundreds of human hours are going away because AI can handle the sponsor portal.""
""In the age of AI, are you as jaw dropping as Claude? And if you're not, that's why you're decaying.""
""It literally sets up meetings for you in your calendar for real that have been confirmed with a human.""
Episode questions
What is the 90/10 rule and when should you break it?
The 90/10 rule is to buy 90% of needed functionality off the shelf and only build the 10% you can't find or that provides outsized value. You should break it when off‑the‑shelf tools are mediocre, lack AI entirely, or when a custom app directly impacts significant revenue or unique proprietary workflows (e.g., sponsor portal, AI VP of Marketing).
How did Claude Cowork change what Amelia could build?
Claude Cowork, running locally and able to inspect the browser, helped Amelia spec, ingest local contract data, and take actions — enabling her to complete the sponsor portal and automate contract processing much faster than before. It served both as an authoring assistant and as an execution aide when she got stuck on technical bits like SSO.
What were the measurable efficiency gains from using an AI agent on sponsor contracts?
What used to take a human a day (reading contracts, creating registration/promo codes, emailing sponsors) was reduced to about one to two hours using Claude Cowork to extract contract data and create codes in the registration system, demonstrating meaningful operational ROI.
What are the main hidden costs of building custom vibe‑coded apps?
Hidden costs include ongoing maintenance, testing (especially for SSO and integrations), feature creep, and the time required from high‑value employees to support and iterate on the app — these can outweigh initial build savings unless the business impact is large.