Open Source Ecosystems

The following article originally appeared on the Asimov’s Addendum Substack and is being reposted here with the author’s permission.

Bill Gurley has an excellent article on what he calls open source strategy, which we recommend reading. There is a lot to debate about his concluding argument in particular: that open-weight models are central to keeping the AI market rent-free. The limits of open-weight AI as the primary open source strategy are surely considerable though, if it still requires expensive hardware to run on, and if the architecture ultimately remains monolithic—rather than composable and protocol-centric.

A related consideration comes from Anthropic’s recent acquisition of Stainless—a startup that generates SDKs, command-line tools, and MCP servers from API specifications. This illustrates that open protocols like MCP, even when publicly governed,¹ remain exposed at their complementary layers to private actors capturing rents. (Protocol openness does not eliminate this and instead probably enables it, by enabling market growth).

We asked Claude to analyze this acquisition, going beyond the press releases. Its first pass overstated parts of the competitive-denial story; what follows is what survived it taking a closer look:

Complement capture, not protocol capture. MCP—the standard that lets AI agents talk to other software—remains open, and its governance has been handed to an independent foundation. What Anthropic bought is the company that turned that standard into something most developers could actually use. Stainless was the dominant tool for taking an ordinary business API (say, a hotel booking system or a customer database) and converting it into something an AI agent could call through MCP. The open standard is still open. The path most developers walked to use it has now been bought.
This isn’t a one-off—the whole layer is consolidating. Stainless wasn’t alone in this market. Its main competitor, Fern, was bought by Postman in January 2026. Anthropic bought Stainless four months later, in May 2026. That leaves Speakeasy as the only major independent player, plus an open-source fallback called OpenAPI Generator that most developers consider too rough for production use without significant manual work. In under five months, two of the three serious companies in this part of the market have been absorbed into larger platforms. The Stainless deal is more visible because of who bought it and why, but the broader pattern matters more: an entire layer of AI infrastructure is being pulled inside platform owners.
Moat migration. The gap in raw model capability between Anthropic, OpenAI, and Google has narrowed considerably and continues to close, and the implication is that model quality alone is unlikely to be the principal basis of competitive advantage over the next two years. What may distinguish the leading firms instead is the quality of the developer experience around their models: how easily a business or an engineer can build something useful on top of a given model, how cleanly the tooling integrates with existing systems, and how reliable the connectors are over time.

Stainless was founded by Alex Rattray, formerly of Stripe. Stripe built its market position largely on unusually well-designed developer tools, and Stainless was, in effect, an attempt to apply the same approach to the layer between AI APIs and the rest of the software economy. Anthropic has acquired the team that knows how to do this.

Pricing logic, with caveats on denial. Stainless was last valued at $150M in December 2025; at >$300M five months later, this is a roughly 2x strategic markup, not acqui-hire arithmetic. Removing a critical-path external dependency on Anthropic’s own SDKs, while denying it to a tight set of competitors, is rational at that price—but the denial logic is partial. Speakeasy is a viable substitute, and OpenAI was reportedly already migrating off Stainless. The friction tax falls hardest on smaller players who lack the engineering bench to absorb migration cost.

…The press release calls it “extending reach”; the InfoWorld read—“last-mile developer experience”—is closer, but the complement-capture component, even if partial, is real.

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Now, while Claude might be overstating some of the market risks associated with this acquisition (you tell us?), it shows that open source’s impacts are highly conditional on its dependencies and should never be analyzed in isolation from the market’s software stack and architecture. This is equally true for open weight models—being dependent on data, compute, and distribution—as it is for open protocols like MCP, dependent on constant API translations and access. Tracking those interdependencies is what a full ecosystem view involves and is helpful to undertake in order to consider where chokepoints might arise, and in turn, where open source strategy might eventually fail or be captured.