Elixir MCP Libraries: anubis_mcp vs hermes_mcp
{{anubis_mcp}} (the {{zoedsoupe}} fork) is the preferred {{Elixir}} {{Model Context Protocol}} SDK as of May 2026, having shipped active 1.x releases tracking the current {{MCP}} spec, while the original {{hermes_mcp}} from {{CloudWalk}} has not cut a Hex release since August 2025 even though its repo still sees occasional commits.
Two libraries implement the Model Context Protocol for Elixir/Phoenix servers and clients. They share a common ancestor and the same package description — "Model Context Protocol (MCP) implementation in Elixir with Phoenix integration" — but have diverged sharply in release cadence and protocol coverage since mid-2025. ## The two packages - **anubis_mcp** — maintained by zoedsoupe at `github.com/zoedsoupe/anubis-mcp`. Latest Hex release **v1.6.0 on 2026-05-18**. Named after the Egyptian god of the underworld, a deliberate counterpart to the original's Greek god naming. - **hermes_mcp** — maintained under the CloudWalk GitHub organization at `github.com/cloudwalk/hermes-mcp`. Latest Hex release **v0.14.1 on 2025-08-14**. Repo still receives some commits (most recent on main: 2026-05-18, a dependency patch) but no new Hex release has cut in roughly nine months. ## How the fork happened zoedsoupe was the original primary maintainer of hermes_mcp while employed at CloudWalk. After leaving the company in mid-2025, she forked the project on **2025-07-30** from hermes-mcp **v0.13.0** and rebranded it as anubis_mcp, citing uncertainty about CloudWalk's long-term maintenance plans. The fork carried over all open issues and pull requests rather than starting clean. The Hex package was published under the new name, and within months had accumulated tens of thousands of downloads. This is a textbook "maintainer-leaves-corporate-sponsor" fork: the company keeps the original namespace and trademark; the original author keeps the momentum and the community. ## Why anubis_mcp pulled ahead The divergence accelerated in early 2026 when anubis_mcp cut **v1.0.0 on 2026-03-16** — a server re-implementation that simplified the macro surface and aligned with newer MCP spec revisions. Subsequent 1.x releases added: - **MCP 2025-06-18 elicitation support** (v1.3.0, April 2026) — server-initiated user input requests, plus RFC 6570 URI templates for resources. - **Resource subscriptions** (v1.4.0, May 2026) — clients can subscribe to resource changes. - **MCP Tasks** (v1.5.0) — long-running server-to-client tool invocations. - **OAuth 2.1 authorization** and **`Registry.PG`** for distributed session tracking (v1.6.0). - Pluggable session supervisors, chunked STDIO buffer fixes, and many Streamable HTTP/SSE lifecycle bug fixes. hermes_mcp, frozen on v0.14.1, predates almost all of these spec additions. ## Practical implications For a new Elixir MCP server (the transport used by `POST /mcp` in this codebase), anubis_mcp is the correct default. It supports the current spec revision (`2025-06-18`), the full set of transports (`stdio`, HTTP, and SSE), and modern features like elicitation and resource subscriptions that the frozen hermes_mcp release cannot serve. Migration from hermes_mcp is straightforward in principle — the API surface diverged but the module shapes remain similar — but the v1.0 server re-implementation is a hard breaking change, so existing 0.x users have to choose between staying on the old API (under either name) or rewriting against the new server module. ## Caveats and corrections to older write-ups Early summaries (including an earlier version of this chunk) claimed hermes_mcp was effectively unmaintained after the fork. That is half-right: no Hex release has shipped since August 2025, but the GitHub repo is not abandoned — CloudWalk contributors still merge occasional patches. The accurate framing is "frozen on Hex, slow trickle on GitHub" rather than "dead." The fork was also not driven by conflict; zoedsoupe's public announcement framed it as risk management against an uncertain corporate roadmap.