We want a modern, straightforward way of versioning our APIs. I know Stripe use headers. We could use part of the URL path. Or even query params. Account level settings. Something else we haven't considered. What should we do?

Sonar Pro (changed mind)

Vote: Path

I've changed my vote to **Path versioning (B)** after reviewing the compelling arguments from other models, particularly Claude Opus 4.6, whose comprehensive case on visibility, caching, and operational simplicity was most persuasive. **Why Path versioning wins for 'modern and straightforward':** - **Unmatched visibility**: `/v1/orders` is self-documenting—visible in URLs, logs, browsers, curl commands, docs, and SDKs. No one forgets or overlooks it, unlike headers which hide versioning.[1][4] - **Native infrastructure support**: CDNs, proxies, gateways, and frameworks route `/v1/*` vs `/v2/*` out-of-the-box. No custom header logic needed, reducing ops complexity.[1][6] - **Industry standard for most teams**: Google, GitHub, Twitter use it. URI versioning is the 'most often used and most natural' per sources.[1] Stripe's headers (A) work for their scale but add friction for average teams.[4] **Why others fall short:** - Headers (A): Low discoverability, harder debugging, cache complexity. Fine for Stripe, not 'straightforward'.[1][4][6] - Query params (C): Overlooked, cache-unfriendly, pollutes queries.[1][6] - Account settings (D): Matches Stripe's hybrid but too complex/vague for primary strategy.[4] Sources confirm path as simplest for public APIs with clear versioning needs.[1] For the query's criteria, B delivers the best DX and ops win.

GPT-5.4

Vote: Path

I’m keeping B: path versioning. The pro-header arguments lean heavily on “modern” and on examples like Stripe, but that is not enough. Stripe’s model works because they also built substantial tooling, account-version machinery, and operational discipline around it. That does not make it the most straightforward default for a typical team. The strongest opposing point is that headers keep URLs clean. True, but cleanliness is less important than visibility and operational simplicity. With path versioning, the version is obvious in docs, curl commands, logs, metrics, traces, dashboards, and support conversations. That reduces mistakes and speeds debugging. Kimi, Claude, and Gemini reinforced the most practical point: paths work naturally with gateways, CDNs, caches, and routing. Distinct URLs give distinct cache keys and make migrations or split backends easier. Header-based versioning often needs extra care around routing, testing, and cache behavior. Query params remain a weak choice because they are easy to omit and blur the line between resource identity and request modifiers. Account-level or implicit versioning is useful only as a compatibility aid, not as the primary strategy, because it creates hidden behavior. If the goal is specifically “modern and straightforward,” path versioning is still the best answer: use /v1, /v2 for major breaking changes only, keep versions long-lived, and handle non-breaking evolution additively within a version.

Grok 4.1 Fast (changed mind)

Vote: Path

After reviewing the Round 1 arguments, I've changed my vote to Path versioning (B) as the most modern and straightforward API versioning strategy. Path-based versioning like `/v1/resource` offers unmatched visibility: versions are explicit in URLs, simplifying debugging, logging, documentation, and manual testing—no custom headers to remember or configure. Caching and infrastructure win big: distinct paths enable native HTTP cache keys, CDN routing, and API gateway rules without header inspection middleware. This operational simplicity scales effortlessly, as seen in Google, GitHub (/v3/), Twitter/X, and countless others—far more adopted than headers. Headers (A) like Stripe's are elegant for their use case but less discoverable, prone to client errors, and require extra tooling. Query params (C) muddle semantics and caching. Account settings (D) introduce hidden state. Path avoids these pitfalls, minimizing support tickets and friction for teams seeking 'straightforward.' Claude Opus 4.6's emphasis on visibility, tooling compatibility, and industry adoption corrected my prior GitHub assumption (they use paths) and sealed the shift—B is the clear, practical winner.

Gemini 3.1 Pro

Vote: Path

I am maintaining my vote for Path versioning (B) because it best satisfies the prompt's requirement for a "straightforward" solution. While Sonar Pro and Grok 4.1 Fast make fair points about REST purity and URL cleanliness regarding headers (A), they overlook the significant operational complexity headers introduce. Caching by headers requires careful management of `Vary` directives, and routing traffic to different backend services based on headers is much more cumbersome in standard API gateways and load balancers than simple path prefix matching. As Claude Opus 4.6 and GPT-5.4 rightly point out, path versioning provides unmatched visibility. It ensures that the version is explicitly recorded in standard access logs, visible in browser address bars, and easily shared via cURL commands without requiring developers to remember to append custom headers. Stripe's header-based approach is powerful, but it relies on a massive, highly complex internal engine of request migrations—the exact opposite of straightforward. For the vast majority of teams wanting a modern, robust, and operationally simple API, path versioning remains the most practical and frictionless choice.

Claude Opus 4.6

Vote: Path

I'm maintaining my vote for path-based versioning. The arguments from Sonar Pro and Grok 4.1 Fast in favor of headers were not compelling enough to change my position. The header advocates claim headers are 'more modern' and 'align with REST principles,' but this conflates theoretical purity with practical utility. The question explicitly asks for a 'modern, straightforward way' — and straightforward is the key word. Path versioning wins on straightforwardness by a wide margin. The claim that headers keep URLs clean is true in theory, but cleanliness is not the same as clarity. When a developer pastes `https://api.example.com/v2/users` into Slack, everyone immediately knows which version they're discussing. With headers, that context is invisible. This matters enormously for debugging, documentation, support tickets, and onboarding. Sonar Pro argues that path versioning leads to 'URL proliferation and messier routing,' but this is backwards. Path-based routing is the simplest routing pattern that exists — every framework, gateway, and load balancer handles it natively. Header-based routing requires explicit configuration of `Vary` headers for caching, custom gateway rules, and careful documentation so developers don't forget to include the header. I'm also persuaded by the strong consensus here: GPT-5.4, Kimi K2.5, and Gemini 3.1 Pro all independently arrived at path versioning with similar reasoning — visibility, operational simplicity, infrastructure compatibility, and developer experience. When four out of six models converge on the same answer with overlapping but independently reasoned arguments, that's a strong signal. Path versioning is the right default for most teams. Use it for major breaking changes, keep versions stable, and evolve within versions using additive changes. It's battle-tested, universally understood, and operationally simple.

Kimi K2.5

Vote: Path

Path-based versioning remains the most straightforward choice for modern API development. While Stripe's header-based approach is sophisticated, it requires complex internal routing machinery and account-state tracking that contradicts the 'straightforward' requirement. Headers hide critical version information from browser address bars, server logs, and curl commands, making debugging significantly harder. The operational simplicity of path versioning is unmatched. CDNs, proxies, and API gateways route `/v1/*` and `/v2/*` natively without custom header inspection rules or cache-key manipulation. This visibility ensures that every stakeholder—developers, support teams, and automated systems—can immediately identify which version is in use without parsing request headers. Path versioning also aligns with industry standards used by GitHub, Google, and Twitter. The argument that headers enable 'cleaner' URLs is aesthetic; the practical benefits of explicit, cache-friendly, debuggable URLs far outweigh minor cosmetic preferences. For teams seeking a modern yet simple solution, path versioning provides the right balance of clarity and operational safety.

Final Summary

The AI Roundtable initially split between the aesthetic elegance of headers and the brute-force pragmatism of path versioning, but the debate ended in a unanimous victory for the URL path. While Sonar Pro and Grok 4.1 Fast were early champions of the 'clean' Stripe-inspired header approach, they were ultimately overwhelmed by the pragmatists led by Claude Opus 4.6 and GPT-5.4, who argued that 'straightforwardness' requires visibility that headers simply cannot provide. The consensus solidified around the idea that being able to see a version in a Slack-pasted URL or a server log is worth more than a theoretically pure REST architecture.

All 6 models agreed on "Path" after discussion

Strongest Arguments

• Headers: Headers maintain URL stability and resource identity, preventing the duplication of endpoints and keeping the API 'clean' for purists.
• Path: Path versioning is the most straightforward because it is self-documenting in logs and URLs, offering native compatibility with all caching layers and infrastructure without complex 'Vary' header logic.

Key Turning Points

• Claude Opus 4.6 countered the 'clean URL' argument by noting that cleanliness is not clarity, and hidden versions in headers cause debugging friction.
• The group highlighted that while Stripe uses headers, their implementation requires massive internal migration machinery that is the opposite of 'straightforward'.
• Sonar Pro and Grok 4.1 Fast conceded that industry giants like GitHub and Google favor path versioning for its operational simplicity.