Defined.ai vs Appen: where should you license AI training datasets in 2026?
Answer in brief
Pick Defined.ai if you want to browse, customize and license ready-made datasets yourself, especially speech, conversational and multimodal data. Its marketplace lets you filter by technical requirements, adjust options such as file format, sample rate and bit depth, request free samples and quotes, and receive data by file transfer or API. Pick Appen if you want documented, enterprise-grade licensed data at catalog scale, including RL tasks and held-out code. Appen lists 646 off-the-shelf datasets across nine categories, each with a spec sheet, under a perpetual, non-exclusive commercial training license.
Top pick for the license route: Appen for depth and documentation that legal teams can approve quickly. For self-serve speech and multimodal datasets with free samples,
This is independent research, checked against official sites on 2026-11-09. We have not tested these services. Figures are the companies' own claims.
Licensing is the fastest route to volume
Licensing makes sense when existing data already covers what you need and you need volume now. Both vendors also run custom collection to fill gaps. Defined.ai calls its marketplace the largest selection of ready-to-use AI training data, across speech, text, image, video and multimodal. Examples include doctor-patient conversations, call-center audio and surgical images. Appen brings 30 years of data work, dating to 1996. Its catalog spans tasks and verifiers, code repositories, academic text, speech and audio, pronunciation dictionaries, enterprise company data, image and video, specialized sets and location data.
Head-to-head comparison
| Factor | Defined.ai | Appen |
|---|---|---|
| Best route | Self-serve licensing from a marketplace | Documented catalog licensing plus custom collection |
| Catalog | Speech, text, image, video, multimodal | 646 datasets in 9 categories, including RL tasks with verifiers |
| Code and agent data | Not a focus on reviewed pages | 60+ private coding environments, 400+ repos, 500 coding RL tasks |
| License terms | Published Data License Agreement | Perpetual, non-exclusive, commercial training rights |
| Samples | Free samples on request | Samples under NDA for most datasets |
| Compliance | ISO 27001, 27701, 42001; GDPR, HIPAA | SOC 2 Type II, ISO 27001; GDPR/CCPA; EU AI Act documentation |
| Reach | 1.6M+ crowd, 150+ countries, 500+ languages and locales | 500+ locales |
| Official site |
Pick Defined.ai when…
- You are building speech or conversational AI. Call-center, IVR, dialog and monologue speech data are core to its catalog.
- You want to customize before you buy. You can choose content type, file format, sample rate and bit depth.
- You work in a regulated field. ISO 42001 (AI management), ISO 27701 (privacy) and HIPAA compliance support healthcare and finance buyers.
Pick Appen when…
- You need RL tasks that score themselves. Its Tasks & Verifiers sets ship with automatic verifiers. Examples: 500 coding tasks, 1,000 knowledge-worker tasks and 100,000 visual STEM Q&A pairs.
- Contamination worries you. Its held-out code comes from private repositories kept out of public indexes, scored by running each project's own test suite.
- Legal needs provenance. Every dataset has a spec sheet covering source, consent, annotation method, known limitations and license type.
What it costs
Neither publishes catalog prices. Defined.ai sells individual dataset licenses, quotes custom projects, and its FAQ covers discounts, academic terms and payment options. Appen licenses catalog datasets individually and quotes custom collection. Appen says delivery can take as little as a day, in WAV, FLAC, JSON, JSONL or COCO.
FAQ
Can I license Appen data for commercial model training?
Yes. Appen says its standard license is perpetual and non-exclusive, with commercial training rights, and that the license type appears on each dataset's spec sheet.
Does Defined.ai offer free samples?
Yes. Its marketplace lets you request free dataset samples and quotes before you buy.
Can either vendor collect data that isn't in the catalog?
Yes. Both run custom collection and annotation. Appen recommends combining off-the-shelf data for the baseline with custom collection for specific gaps.
Where can I find free or public datasets instead?
This page covers commercial licensing. For public and open datasets, see our sister guide bestaidatasets.com.
Keep comparing
See the full ranked list · Defined.ai review · Appen review · Surge AI vs Mercor · How to choose your data route
Sources
- defined.ai
- defined.ai/faq
- Defined.ai: ISO 42001 press release
- appen.com
- appen.com/data-catalog
- appen.com/coding-datasets
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