diff --git a/.changeset/probe-lexicons.md b/.changeset/probe-lexicons.md
new file mode 100644
index 0000000..37e4411
--- /dev/null
+++ b/.changeset/probe-lexicons.md
@@ -0,0 +1,5 @@
+---
+"@getcirrus/space-conformance": patch
+---
+
+Probe spaces now use published, resolvable lexicons (`earth.cirrus.check.space` / `.note` / `.withblob`) instead of the unpublished `app.bsky.group` type and unresolvable `test.conformance.*` collections, so the suite works against implementations that resolve lexicons dynamically and validate strictly — not only against lenient targets.
diff --git a/apps/check/src/App.tsx b/apps/check/src/App.tsx
index c5607f0..60f495f 100644
--- a/apps/check/src/App.tsx
+++ b/apps/check/src/App.tsx
@@ -751,13 +751,15 @@ function ConfirmSpacesView(props: {
 						<ul class="space-y-2 pl-4">
 							<li>
 								<span class="text-ink">·</span> Create probe spaces of type{" "}
-								<code class="bg-line/40 px-1 py-0.5">app.bsky.group</code> with
-								run-unique keys, deleted at the end of each check
+								<code class="bg-line/40 px-1 py-0.5">
+									earth.cirrus.check.space
+								</code>{" "}
+								with run-unique keys, deleted at the end of each check
 							</li>
 							<li>
 								<span class="text-ink">·</span> Write and delete records in the
 								neutral{" "}
-								<code class="bg-line/40 px-1 py-0.5">test.conformance.*</code>{" "}
+								<code class="bg-line/40 px-1 py-0.5">earth.cirrus.check.*</code>{" "}
 								collections inside those probe spaces
 							</li>
 							<li>
diff --git a/apps/check/src/lib/oauth.ts b/apps/check/src/lib/oauth.ts
index 2d5771e..298e466 100644
--- a/apps/check/src/lib/oauth.ts
+++ b/apps/check/src/lib/oauth.ts
@@ -23,7 +23,7 @@ const SCOPE = "atproto transition:generic";
  * suite is meaningless there.
  */
 const SPACE_SCOPE =
-	"space:app.bsky.group?collection=*&manage=create&manage=update&manage=delete";
+	"space:earth.cirrus.check.space?collection=*&manage=create&manage=update&manage=delete";
 export const SPACES_SCOPE = `${SCOPE} ${SPACE_SCOPE}`;
 
 const CALLBACK_PATH = "/oauth/callback";
diff --git a/apps/check/src/worker.ts b/apps/check/src/worker.ts
index c71a7eb..91c33f5 100644
--- a/apps/check/src/worker.ts
+++ b/apps/check/src/worker.ts
@@ -29,7 +29,7 @@ function clientMetadata(origin: string): Record<string, unknown> {
 		// the write tests, the OAuth conformance flow, and the spaces
 		// conformance run each request a subset of this registration.
 		scope:
-			"atproto transition:generic repo:earth.cirrus.check.testrecord include:site.standard.authFull space:app.bsky.group?collection=*&manage=create&manage=update&manage=delete",
+			"atproto transition:generic repo:earth.cirrus.check.testrecord include:site.standard.authFull space:earth.cirrus.check.space?collection=*&manage=create&manage=update&manage=delete",
 		grant_types: ["authorization_code", "refresh_token"],
 		response_types: ["code"],
 		application_type: "web",
diff --git a/packages/space-conformance/probe-lexicons/README.md b/packages/space-conformance/probe-lexicons/README.md
new file mode 100644
index 0000000..dd95473
--- /dev/null
+++ b/packages/space-conformance/probe-lexicons/README.md
@@ -0,0 +1,57 @@
+# Probe lexicons
+
+The suite's probe spaces use the space type `earth.cirrus.check.space` and
+write records in `earth.cirrus.check.note` / `earth.cirrus.check.withblob`.
+These NSIDs are **published, resolvable lexicons** — this directory holds
+the canonical documents.
+
+## Why published probes matter
+
+An earlier iteration used `app.bsky.group` (the proposal's example type)
+and deliberately-unresolvable `test.conformance.*` collections. That works
+against implementations that are lenient about unresolvable lexicons
+(Cirrus, the reference alpha) but fails against any implementation that
+resolves lexicons dynamically and validates strictly — reported by a
+third-party implementer running the web checker. A conformance suite must
+not depend on the target's leniency, so the probe NSIDs live under an
+authority the suite's maintainers control and resolve for everyone. The
+probe collections are still invisible to Bluesky: nothing under
+`earth.cirrus.check.*` is an `app.bsky.*` lexicon, so AppViews ignore it.
+
+## How they are published
+
+Lexicon resolution is two steps: DNS names the authority, the authority's
+repo holds the schema records.
+
+1. DNS, on the `check.cirrus.earth` zone (covers every
+   `earth.cirrus.check.*` NSID):
+
+   ```
+   _lexicon.check.cirrus.earth.  TXT  "did=did:plc:uwbl4k3tza7eyjv3morkrld2"
+   ```
+
+2. One `com.atproto.lexicon.schema` record per NSID in that DID's repo,
+   rkey = the NSID, value = the JSON document in this directory.
+
+To (re)publish after editing a document here, with the maintainer's PDS
+token in `$AUTH_TOKEN`, from this directory:
+
+```sh
+for f in earth.cirrus.check.space earth.cirrus.check.note earth.cirrus.check.withblob; do
+  curl -s -X POST https://mk.pds.mk.gg/xrpc/com.atproto.repo.putRecord \
+    -H "Authorization: Bearer $AUTH_TOKEN" -H 'Content-Type: application/json' \
+    -d "$(python3 -c "import json;print(json.dumps({
+      'repo':'did:plc:uwbl4k3tza7eyjv3morkrld2',
+      'collection':'com.atproto.lexicon.schema',
+      'rkey':'$f',
+      'record':json.load(open('$f.json'))}))")"
+  echo " $f"
+done
+```
+
+Verify resolution end-to-end:
+
+```sh
+dig +short TXT _lexicon.check.cirrus.earth
+curl -s "https://mk.pds.mk.gg/xrpc/com.atproto.repo.getRecord?repo=did:plc:uwbl4k3tza7eyjv3morkrld2&collection=com.atproto.lexicon.schema&rkey=earth.cirrus.check.space"
+```
diff --git a/packages/space-conformance/probe-lexicons/earth.cirrus.check.note.json b/packages/space-conformance/probe-lexicons/earth.cirrus.check.note.json
new file mode 100644
index 0000000..4ec10b6
--- /dev/null
+++ b/packages/space-conformance/probe-lexicons/earth.cirrus.check.note.json
@@ -0,0 +1,19 @@
+{
+	"$type": "com.atproto.lexicon.schema",
+	"lexicon": 1,
+	"id": "earth.cirrus.check.note",
+	"defs": {
+		"main": {
+			"type": "record",
+			"description": "A disposable probe record written into a probe space by the space conformance suite, deleted with the space.",
+			"key": "any",
+			"record": {
+				"type": "object",
+				"required": ["text"],
+				"properties": {
+					"text": { "type": "string", "maxLength": 1000 }
+				}
+			}
+		}
+	}
+}
diff --git a/packages/space-conformance/probe-lexicons/earth.cirrus.check.space.json b/packages/space-conformance/probe-lexicons/earth.cirrus.check.space.json
new file mode 100644
index 0000000..cc92625
--- /dev/null
+++ b/packages/space-conformance/probe-lexicons/earth.cirrus.check.space.json
@@ -0,0 +1,13 @@
+{
+	"$type": "com.atproto.lexicon.schema",
+	"lexicon": 1,
+	"id": "earth.cirrus.check.space",
+	"defs": {
+		"main": {
+			"type": "space",
+			"name": "Conformance probe space",
+			"description": "Ephemeral probe spaces created by the @getcirrus/space-conformance suite (check.cirrus.earth). Each is created with a run-unique key and deleted when its check finishes.",
+			"collections": ["earth.cirrus.check.note", "earth.cirrus.check.withblob"]
+		}
+	}
+}
diff --git a/packages/space-conformance/probe-lexicons/earth.cirrus.check.withblob.json b/packages/space-conformance/probe-lexicons/earth.cirrus.check.withblob.json
new file mode 100644
index 0000000..68b639f
--- /dev/null
+++ b/packages/space-conformance/probe-lexicons/earth.cirrus.check.withblob.json
@@ -0,0 +1,19 @@
+{
+	"$type": "com.atproto.lexicon.schema",
+	"lexicon": 1,
+	"id": "earth.cirrus.check.withblob",
+	"defs": {
+		"main": {
+			"type": "record",
+			"description": "A probe record referencing a blob, used by the space conformance suite to verify space blobs are not served publicly. Deleted with its probe space.",
+			"key": "any",
+			"record": {
+				"type": "object",
+				"required": ["file"],
+				"properties": {
+					"file": { "type": "blob", "maxSize": 1048576 }
+				}
+			}
+		}
+	}
+}
diff --git a/packages/space-conformance/src/checks/base.ts b/packages/space-conformance/src/checks/base.ts
index 8b4481b..96a816a 100644
--- a/packages/space-conformance/src/checks/base.ts
+++ b/packages/space-conformance/src/checks/base.ts
@@ -71,7 +71,7 @@ const authGetRecordRequiresAuth = defineCheck({
 		// all (there's simply no record at this probe URI to leak), and a 5xx
 		// is a server fault, not a refusal — neither demonstrates enforcement.
 		const res = await xrpcGet(ctx, "com.atproto.space.getRecord", {
-			space: `at://${ctx.target.did}/space/app.bsky.group/probe`,
+			space: `at://${ctx.target.did}/space/earth.cirrus.check.space/probe`,
 			repo: ctx.target.did,
 			collection: "app.bsky.feed.post",
 			rkey: "whatever",
@@ -96,7 +96,7 @@ const authCredentialRequiresToken = defineCheck({
 	needs: [],
 	async run(ctx) {
 		const res = await xrpcPost(ctx, "com.atproto.space.getSpaceCredential", {
-			space: `at://${ctx.target.did}/space/app.bsky.group/probe`,
+			space: `at://${ctx.target.did}/space/earth.cirrus.check.space/probe`,
 		});
 		if (res.status === 401 || res.status === 403 || res.status === 400) {
 			return pass(`refused with ${res.status} ${res.error ?? ""}`);
diff --git a/packages/space-conformance/src/checks/operator.ts b/packages/space-conformance/src/checks/operator.ts
index 372b648..f3fd836 100644
--- a/packages/space-conformance/src/checks/operator.ts
+++ b/packages/space-conformance/src/checks/operator.ts
@@ -30,13 +30,14 @@ import {
 import { createDpopKey, createDpopProofJwt } from "../dpop.js";
 import { readCarHeader } from "../car.js";
 
-// A collection with no loaded lexicon, so record validation is
-// optimistic (fail-open) on any conformant target — the checks probe
-// space behaviour, not Bluesky schema validation.
-export const POST = "test.conformance.note";
+// The probe collections and space type are published, resolvable
+// lexicons under the suite's own authority (see ../../probe-lexicons) —
+// so strict, dynamically-resolving targets can validate them, while
+// AppViews ignore them (nothing under earth.cirrus.check.* is app.bsky.*).
+export const POST = "earth.cirrus.check.note";
 export const note = (text: string) => ({ $type: POST, text });
 
-const PROBE_TYPE = "app.bsky.group";
+const PROBE_TYPE = "earth.cirrus.check.space";
 
 export interface ProbeSpace {
 	uri: string;
@@ -693,7 +694,7 @@ const simplespaceUnsupportedPolicy = defineCheck({
 			asOperator(ctx),
 			"com.atproto.simplespace.createSpace",
 			{
-				type: "app.bsky.group",
+				type: PROBE_TYPE,
 				policy: { $type: "com.example.mysteryPolicy" },
 				appAccess: { $type: "com.atproto.simplespace.defs#open" },
 			},
@@ -805,10 +806,10 @@ const blobsSpaceNotPublic = defineCheck({
 			const write = await operatorCreateRecord(
 				ctx,
 				space.uri,
-				"test.conformance.withblob",
+				"earth.cirrus.check.withblob",
 				"self",
 				{
-					$type: "test.conformance.withblob",
+					$type: "earth.cirrus.check.withblob",
 					file: blob,
 				},
 			);
diff --git a/packages/space-conformance/src/cli/oauth.ts b/packages/space-conformance/src/cli/oauth.ts
index 3947c87..f180629 100644
--- a/packages/space-conformance/src/cli/oauth.ts
+++ b/packages/space-conformance/src/cli/oauth.ts
@@ -26,7 +26,7 @@ import {
  * space type under the user's own authority. Mirrors the web checker.
  */
 const OAUTH_SCOPE =
-	"atproto transition:generic space:app.bsky.group?collection=*&manage=create&manage=update&manage=delete";
+	"atproto transition:generic space:earth.cirrus.check.space?collection=*&manage=create&manage=update&manage=delete";
 
 /** How long to wait for the user to complete the browser flow. */
 const CALLBACK_TIMEOUT_MS = 5 * 60 * 1000;