--- title: Why Are .NET Libraries Going Paid? The Open Source Cost... description: A number of prominent .NET libraries (Polly, AutoMapper, MediatR, Fluent Assertions, MassTransit) have introduced paid licensing or maintenance fees, with... canonical: https://daily.dev/posts/why-are-net-libraries-going-paid-the-open-source-cost-ai-can-t-erase-bnptxyznc twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Why Are .NET Libraries Going Paid? The Open Source Cost AI Can’t Erase | daily.dev og:description: A number of prominent .NET libraries (Polly, AutoMapper, MediatR, Fluent Assertions, MassTransit) have introduced paid licensing or maintenance fees, with... og:url: https://daily.dev/posts/why-are-net-libraries-going-paid-the-open-source-cost-ai-can-t-erase-bnptxyznc og:image: https://api.daily.dev/og/posts/BNPtXyZNC.png og:image:alt: Why Are .NET Libraries Going Paid? The Open Source Cost AI Can’t Erase og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Why Are .NET Libraries Going Paid? The Open Source Cost AI Can’t Erase **[We Are .NET](https://daily.dev/sources/wearedotnet)** · 12 min read · 8 upvotes · 0 comments ## Summary A number of prominent .NET libraries (Polly, AutoMapper, MediatR, Fluent Assertions, MassTransit) have introduced paid licensing or maintenance fees, with Polly announcing a $20/month Open Source Maintenance Fee starting November 16, 2026, for organizations earning over $20,000 in annual revenue from products using its maintained releases. The piece argues these shifts are not interchangeable: some keep source open while charging for maintained binaries, others require paid licenses only for newer major versions. It walks through what the Polly fee does and doesn't cover (maintenance, not SLA or support), how transitive dependencies (like Microsoft.Extensions.Http.Resilience pulling in Polly) are treated differently from direct references, and argues that AI lowers the cost of writing replacement code but doesn't eliminate the ongoing cost of ownership — security review, compatibility, documentation, and operational judgment. It closes with a five-question framework for evaluating whether to keep, fork, replace, or pay for a critical dependency. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### What is the Polly Open Source Maintenance Fee and when does it start? Polly announced a $20 per month Open Source Maintenance Fee for qualifying organizations using its maintained releases, with payment requests planned to begin November 16, 2026. The fee applies per organization (not per developer or server) when a company has at least one product generating $20,000 or more in annual revenue. The source code itself stays under its existing open-source license. _Teams tracking dependency cost changes like this can follow library licensing shifts on daily.dev._ ### Do I have to pay the Polly maintenance fee if I only use Polly as a transitive dependency through Microsoft.Extensions.Http.Resilience? No, under the general OSMF guidance, consumers are expected to pay only for projects they directly choose, not for dependencies pulled in solely because another package needs them. So an application whose only connection to Polly is through Microsoft's resilience package is treated differently than one that directly references Polly. Adding any direct Polly reference elsewhere changes that analysis. _Developers untangling dependency graphs and licensing obligations can track these distinctions on daily.dev._ ### How do AutoMapper, MediatR, Fluent Assertions, and MassTransit licensing changes differ from Polly's approach? AutoMapper 15 and MediatR 13 adopted Lucky Penny licensing while earlier versions stay open source; Fluent Assertions 8 requires a paid license for commercial use while version 7 remains open source with important fixes; MassTransit v9 is a commercial release with earlier open-source versions still available. Polly took a different route, keeping its source license unchanged and instead attaching a fee to its maintainer-provided releases rather than closing the source. _Architects comparing licensing models across .NET libraries can track these shifts on daily.dev._ ## Similar posts on daily.dev - [Stop Your AI Agent Picking the Wrong .NET Libraries](https://daily.dev/posts/stop-your-ai-agent-picking-the-wrong-net-libraries-m6tagi9al) · Code with Mukesh · 3 upvotes · 0 comments - [The .NET OSS Relicensing Panic Is an Incentives Problem](https://daily.dev/posts/the-net-oss-relicensing-panic-is-an-incentives-problem-5v2b1bkv0) · Aaronontheweb · 0 upvotes · 0 comments --- Tags: [#open-source](https://daily.dev/tags/open-source), [#.net](https://daily.dev/tags/.net), [#licensing](https://daily.dev/tags/licensing) [View this post on daily.dev](https://daily.dev/posts/why-are-net-libraries-going-paid-the-open-source-cost-ai-can-t-erase-bnptxyznc) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Why Are .NET Libraries Going Paid? 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