Choosing a travel API is one of the most consequential technical decisions for any platform that offers flight booking. The wrong choice means months of integration work, incomplete coverage, and customer complaints. The right choice means a single integration that covers the global market.
In 2026, the landscape has consolidated around four major approaches. Here's how they compare — honestly, including our own product.
The Quick Comparison
| Feature | Duffel | Amadeus | Kiwi / Tequila | RunRelay |
|---|---|---|---|---|
| API Style | REST / Modern | REST + SOAP | REST | REST + MCP |
| GDS Coverage | ✓ Good | ✓ Best | ~ Partial | ✓ Full |
| NDC Coverage | ✓ Growing | ✓ Good | ✗ Limited | ✓ Good |
| LCC Coverage | ✗ No | ✗ No | ~ Some | ✓ Full |
| Pricing Model | Per booking | Enterprise license | Commission | Per booking |
| Integration Time | 1-2 weeks | 2-6 months | 1-2 weeks | 1-2 weeks |
| Human Concierge | ✗ No | ✗ No | ✗ No | ✓ 24/7 |
| Hotels | ✗ No | ✓ Yes | ✓ Yes | ✓ Yes |
| Ancillaries (Lounges, eSIM) | ✗ No | ~ Some | ✗ No | ✓ Full |
| MCP / AI Agent Support | ✗ No | ✗ No | ✗ No | ✓ Native |
| White Label Platform | ✗ No | ~ Partners | ✗ No | ✓ Yes |
| Disruption Handling | ✗ Self-service | ~ Notifications | ~ Guarantee | ✓ Proactive |
Duffel: The Developer-Friendly Modern API
Duffel launched as the "Stripe for flights" — a modern REST API with excellent documentation, clean data models, and a developer experience that makes GDS integration feel almost pleasant. For teams that need standard airline content with a modern API, Duffel is a strong choice.
What Duffel does well:
- Beautiful, well-documented REST API
- Clean data models with good TypeScript/Python SDKs
- Growing NDC airline coverage
- Transparent per-booking pricing
- Fast integration — realistically 1-2 weeks to first booking
Where Duffel falls short:
- No LCC coverage. Ryanair, Wizz Air, EasyJet, Spirit — none of them are available through Duffel. This means 40%+ of European short-haul is missing.
- Flights only. No hotels, no lounges, no insurance, no ancillary services beyond what airlines offer via NDC.
- No human support layer. When things go wrong — cancellations, rebooking, edge cases — it's on your team to handle it.
- No AI/MCP integration. Pure REST API with no native support for AI agent protocols.
Duffel is ideal for: startups building flight-search products who don't need LCC coverage or concierge services.
Amadeus: The Enterprise Standard
Amadeus for Developers is the API layer on top of the world's largest GDS. If you need the deepest possible airline content — including complex itineraries, codeshares, interline agreements, and corporate fares — Amadeus is unmatched.
What Amadeus does well:
- Broadest GDS content available anywhere
- Support for complex itineraries, multi-city, codeshare
- Hotel, car rental, and ancillary APIs available
- Established enterprise support and SLAs
- Growing NDC hub with major airline connections
Where Amadeus falls short:
- Complexity. The API surface is enormous and inconsistent. Some endpoints are modern REST, others are thinly wrapped SOAP/XML. Integration can take 2-6 months for a full implementation.
- Cost. Enterprise licensing with minimums. Not viable for startups or low-volume platforms.
- No LCC coverage. Same fundamental gap as every GDS — LCCs don't participate.
- No concierge layer. Amadeus is infrastructure, not a service. You build and operate everything on top.
Amadeus is ideal for: large enterprises with dedicated travel technology teams who need maximum GDS content.
Kiwi / Tequila: The Virtual Interlining Pioneer
Kiwi.com's Tequila API pioneered virtual interlining — combining flights from different airlines into single itineraries, even when the airlines have no commercial relationship. This enables unique routing combinations that no other provider can offer.
What Kiwi does well:
- Virtual interlining — unique combined itineraries
- Some LCC coverage through partnerships
- Kiwi Guarantee for missed connections on combined itineraries
- Good coverage in European and Asian markets
Where Kiwi falls short:
- Access restrictions. Since 2024, Tequila has been largely invite-only, with new partners requiring approval and minimum volume commitments.
- Unpredictable pricing. Commission-based model means your margin depends on Kiwi's markup, which can vary significantly.
- Limited direct booking control. You're booking through Kiwi's system, not directly with airlines — which can complicate post-booking servicing.
- No concierge or white-label options. Kiwi is an API, not a platform.
Kiwi is ideal for: platforms focused on budget travel and unique routing that can meet Kiwi's volume requirements.
RunRelay: GDS + NDC + LCC + Human Concierge
Full disclosure: we built RunRelay because the options above all have the same fundamental gap — none of them offer complete market coverage with a service layer.
What RunRelay does:
- Unified distribution. GDS content for full-service carriers, NDC for airline-direct fares, and human-assisted booking for LCCs — all through a single REST API.
- Full lifecycle management. Search, book, modify, cancel, and handle disruptions — including proactive rebooking when flights are cancelled.
- 24/7 human concierge. Every booking has a human layer for edge cases, disruption handling, and special requests. This isn't an add-on — it's built into the API.
- Beyond flights. Hotels, airport lounges, eSIM, travel insurance, ground transfers — everything a traveler needs, through one integration.
- MCP native. Production MCP server with 9 tools for AI agent integration. Your Claude or GPT agent can search and book flights out of the box.
- White-label platform. For banks and fintechs, a turnkey branded portal that launches in 2 weeks with zero development effort.
Where RunRelay has trade-offs:
- LCC booking is asynchronous. Because human operators book on airline websites, LCC confirmation takes 5-15 minutes instead of being instant. For most use cases, this is acceptable. For real-time price comparison without booking intent, it's a constraint.
- Newer platform. RunRelay doesn't have the decades of track record that Amadeus has. We compensate with transparency, direct access to our team, and rapid iteration.
- Not the cheapest for high-volume, GDS-only use cases. If you only need GDS content and don't care about LCCs, concierge, or ancillaries, Duffel may be more cost-effective.
Which API Should You Choose?
The answer depends on what you're building:
- If you need a quick, modern flights-only API and don't need LCC coverage → Duffel
- If you're an enterprise with a large travel tech team and need maximum GDS depth → Amadeus
- If you need creative routing and virtual interlining and can meet volume requirements → Kiwi
- If you need complete market coverage (including LCCs), human concierge, AI agent support, and/or a white-label platform → RunRelay
The question isn't "which API has the best documentation?" It's "which API can my customers actually book all their flights through?" If the answer needs to include Ryanair, Wizz Air, and EasyJet, the choice narrows significantly.