diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index daa7cad..955c102 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -34,6 +34,33 @@ jobs:
       - run: npm ci
       - run: npm run format:check
 
+  # ──────────────────────────────────────────────────────────
+  # Oh My Pi host compatibility — real omp binary, mock API
+  # ──────────────────────────────────────────────────────────
+  omp-compat:
+    name: Oh My Pi compatibility
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+      - uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: latest
+      - run: npm ci
+      - name: Install Oh My Pi
+        run: |
+          npm install -g @oh-my-pi/pi-coding-agent@latest
+          echo "OMP_BIN=$(npm prefix -g)/bin/omp" >> "$GITHUB_ENV"
+      - name: Verify omp starts
+        run: '"$OMP_BIN" --version'
+      - name: Run OMP compatibility suite
+        env:
+          OMP_COMPAT_REQUIRED: "1"
+        run: node tests/test-omp-compat.mjs
+
   # ──────────────────────────────────────────────────────────
   # Code-level vulnerability scanning (SAST)
   # ──────────────────────────────────────────────────────────
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 279f22b..ad2cb35 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+- Fix `omp plugin install` on Oh My Pi 18.x, which rejected 0.6.1 because its pi-ai lacks the `registerApiProvider` export; the compat registration now resolves at runtime and is skipped on hosts that register custom APIs themselves.
+- Run the Oh My Pi compatibility suite against a real `omp` binary in CI as a required check, and assert there that the extension loads against OMP's bundled pi packages.
+
 ## 0.6.1 - 2026-09-01
 
 - Expose selectable thinking levels (`minimal`, `low`, `medium`, `high`, `xhigh`) for `meta/muse-spark-1.1`, `meta/muse-spark-1.2`, and `meta/muse-spark-1.2-contributor` through a manual catalog override, so `/thinking` and `Shift+Tab` no longer stay locked on `off` for these reasoning models.
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 0a6b84f..32a9171 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -52,6 +52,17 @@ COMMANDCODE_E2E_PROVIDER_API_KEY_FILE=/path/to/provider-key npm run test:e2e:liv
 
 Use `npm run test:e2e:live:all` with the Go and GOAT file variables to run both subscription transports sequentially. Store keys in a secret manager and export each one to a new mode-`0600` temporary file for the test; never add key files to the repository. Direct `*_API_KEY` variables are intended primarily for protected CI secrets.
 
+### Oh My Pi compatibility
+
+`tests/test-omp-compat.mjs` runs the extension inside a real `omp` binary against a mock Command Code API. It skips locally when `omp` is not on `PATH`; CI installs Oh My Pi and runs it as a required check with `OMP_COMPAT_REQUIRED=1`, so a change that only loads on pi fails CI instead of the next `omp plugin install`.
+
+To run it locally, point `OMP_BIN` at an omp executable (Oh My Pi needs Bun ≥ 1.3.14):
+
+```sh
+npm install -g @oh-my-pi/pi-coding-agent
+OMP_BIN="$(npm prefix -g)/bin/omp" node tests/test-omp-compat.mjs
+```
+
 Before opening a PR, run:
 
 ```sh
diff --git a/index.ts b/index.ts
index 12af76c..89a9816 100644
--- a/index.ts
+++ b/index.ts
@@ -6,11 +6,8 @@
  */
 
 import { AssistantMessageEventStream } from "@earendil-works/pi-ai"
-import {
-  registerApiProvider,
-  streamSimple as streamNativeProvider,
-  type ApiStreamSimpleFunction,
-} from "@earendil-works/pi-ai/compat"
+import * as piAiCompat from "@earendil-works/pi-ai/compat"
+import { streamSimple as streamNativeProvider } from "@earendil-works/pi-ai/compat"
 import {
   getAgentDir,
   type ExtensionAPI,
@@ -45,6 +42,24 @@ import { createCommandCodeTransportRouter } from "./src/transport.ts"
 const COMMAND_CODE_API = "commandcode-custom"
 const COMPAT_SOURCE_ID = "pi-commandcode-provider"
 
+type CompatStreamFunction = (
+  model: Parameters<typeof streamNativeProvider>[0],
+  context: Parameters<typeof streamNativeProvider>[1],
+  options?: Parameters<typeof streamNativeProvider>[2],
+) => AssistantMessageEventStream
+
+/**
+ * pi's compat entrypoint exposes `registerApiProvider`; Oh My Pi maps
+ * `@earendil-works/pi-ai/compat` onto its own pi-ai, which lacks that export
+ * and registers custom APIs itself inside `registerProvider`. Resolve the
+ * function at runtime so the extension loads on both hosts.
+ */
+function registerCompatApiProvider(stream: CompatStreamFunction): void {
+  const register = (piAiCompat as { registerApiProvider?: unknown }).registerApiProvider
+  if (typeof register !== "function") return
+  register({ api: COMMAND_CODE_API, stream, streamSimple: stream }, COMPAT_SOURCE_ID)
+}
+
 function commandCodeHeaders(): Record<string, string> | undefined {
   if (process.env.CMD_ZDR === "1" || process.env.COMMANDCODE_ZDR === "1") {
     return { "x-cmd-zdr": "1" }
@@ -135,16 +150,13 @@ export default async function (pi: ExtensionAPI) {
   // custom api there so those calls reach the same transport. The registry
   // resolves no credentials for extension providers, so fall back to the
   // configured key when the caller passes none.
-  const compatStream: ApiStreamSimpleFunction = (model, context, options) =>
+  const compatStream: CompatStreamFunction = (model, context, options) =>
     transport.stream(
       model,
       context,
       options?.apiKey ? options : { ...options, apiKey: getConfiguredApiKey() },
     ) as AssistantMessageEventStream
-  registerApiProvider(
-    { api: COMMAND_CODE_API, stream: compatStream, streamSimple: compatStream },
-    COMPAT_SOURCE_ID,
-  )
+  registerCompatApiProvider(compatStream)
 
   pi.on("message_end", async (event, ctx) => {
     if (event.message.role !== "assistant") return
diff --git a/tests/test-omp-compat.mjs b/tests/test-omp-compat.mjs
index ced7c03..4dc4cce 100644
--- a/tests/test-omp-compat.mjs
+++ b/tests/test-omp-compat.mjs
@@ -40,6 +40,10 @@ function findOmpBinary() {
 
 const OMP_BIN = findOmpBinary()
 if (!OMP_BIN) {
+  if (process.env.OMP_COMPAT_REQUIRED === "1") {
+    console.error("[omp-compat] FAIL - omp is required but not on PATH and OMP_BIN is unset")
+    process.exit(1)
+  }
   console.log("[omp-compat] SKIP - omp is not on PATH")
   process.exit(0)
 }
@@ -211,6 +215,20 @@ function runOmp(args, timeoutMs = 30_000) {
 }
 
 try {
+  console.log("[omp-compat] extension loads against the host's pi packages")
+  // OMP remaps `@earendil-works/pi-ai/compat` onto its own pi-ai and rejects
+  // any named import that module does not export, both in `omp plugin
+  // install` validation and when loading the extension. 0.6.1 shipped such an
+  // import and could not be installed on omp 18 (#74). `omp models -e EXT`
+  // runs the same loader, so it reproduces that failure without a registry.
+  const load = await runOmp(["models", "-e", EXT_PATH])
+  assert.equal(load.code, 0, load.stderr)
+  assert.doesNotMatch(
+    load.stdout + load.stderr,
+    /Failed to load extension|not found in module/,
+    "the extension must only import what OMP's bundled pi packages export",
+  )
+
   console.log("[omp-compat] list models through real extension")
   modelListRequestCount = 0
   // Prefer the flag form `omp -e EXT --list-models`; Homebrew's `omp`