Stammer AI vs CustomGPT: Which RAG-Based AI Chatbot Is Better for Agencies?

Choosing between Stammer AI vs CustomGPT comes down to what your agency actually needs. Stammer AI targets agencies that want to resell white-label AI chatbots under their own brand, while CustomGPT focuses on enterprises that need highly accurate, multi-source RAG-powered AI assistants. Both platforms serve distinct audiences, and neither is a perfect fit for every agency use case. In this comparison, we break down features, pricing, and RAG capabilities across all three platforms, including Robofy, which is purpose-built for agency resellers who want zero per-message fees and full revenue control.

What is Stammer AI?

Stammer AI is a white-label AI chatbot and voice platform built primarily for digital agencies. It lets agencies create branded AI agents and resell them to clients under a custom domain and logo. Plans range from $49/mo for the Starter tier (which does not include white-label features) up to $497/mo for the Full SaaS plan with unlimited agents and sub-accounts. The Agency plan at $197/mo supports 30 agents and 30 sub-accounts. Stammer charges per-message fees on top of the subscription, adding cost complexity as usage scales.

What is CustomGPT?

CustomGPT.ai is a no-code platform that lets businesses build custom AI assistants trained on their own data using retrieval augmented generation (RAG). It supports an impressive range of data sources including websites, PDFs, Word documents, Excel files, YouTube videos, Confluence pages, and Zendesk articles. CustomGPT emphasizes accuracy with built-in anti-hallucination controls and citation tracking across 90+ languages. However, white-label branding is only available on the Premium plan at $499/mo, making it one of the more expensive entry points for agencies. The Standard plan at $99/mo includes no white-label support at all. CustomGPT is not designed specifically for agency reselling.

Stammer AI vs CustomGPT vs Robofy: Feature Comparison

Robofy leads on agency-specific features, combining white-label branding with a dedicated reseller program and no per-message fees. Stammer AI offers voice AI that neither Robofy nor CustomGPT fully matches. CustomGPT excels at multi-source accuracy but lacks a genuine agency reseller framework, and its white-label tier is the most expensive of the three.

Pricing Comparison

CustomGPT's $99/mo Standard plan may look attractive at first glance, but agencies need to note that white-label is completely absent at that tier. Agencies must jump to $499/mo just to offer branded AI to clients, making it the most expensive white-label entry point among the three. Stammer AI's per-message fees can quickly compound costs for high-traffic deployments. Robofy's flat reseller cost with no per-message billing gives agencies predictable margins and full revenue retention.

RAG Capabilities: CustomGPT vs Stammer vs Robofy

CustomGPT is the strongest performer when it comes to raw RAG training flexibility. It ingests websites, PDFs, Word documents, Excel files, YouTube transcripts, Confluence, and Zendesk, making it a top choice for enterprises with complex, distributed knowledge bases. Its citation tracking and anti-hallucination architecture are mature and well-documented. Stammer AI also supports multi-source training but with fewer native integrations and less emphasis on accuracy controls. Robofy supports website and document-based RAG training suitable for most agency client deployments. For agencies whose clients do not have highly complex enterprise data sources, Robofy's RAG capabilities cover the vast majority of real-world needs at a significantly lower cost.

Which Is Better for Your Agency?

If your agency's priority is accurate AI assistants trained across complex enterprise data sources and you can absorb a $499/mo white-label cost, CustomGPT is the strongest RAG-focused option. If voice AI is essential and you are comfortable managing per-message billing, Stammer AI fills that gap. For agencies focused on building a scalable chatbot reseller business with predictable costs, zero per-message fees, full revenue retention, and a dedicated reseller program, Robofy is the clear winner. It removes the billing complexity of Stammer and the prohibitive white-label pricing of CustomGPT, giving agencies the best economics for growing a recurring-revenue AI business.