diff --git a/packages/core/src/options.ts b/packages/core/src/options.ts
index 7661267e..854fa3c5 100644
--- a/packages/core/src/options.ts
+++ b/packages/core/src/options.ts
@@ -24,7 +24,7 @@ export function makeSavedSessionOptions(opts: SavedSessionOptions): Required<Sav
   return {
     enabled: true,
     maxAge: 86400,
-    storagePrefix: 'thebe-binder-',
+    storagePrefix: 'thebe-binder',
     ...opts,
   };
 }
diff --git a/packages/core/tests/config.spec.ts b/packages/core/tests/config.spec.ts
index 36151556..ba5778b1 100644
--- a/packages/core/tests/config.spec.ts
+++ b/packages/core/tests/config.spec.ts
@@ -32,7 +32,7 @@ describe('config', () => {
       expect(config.savedSessions).toEqual({
         enabled: true,
         maxAge: 86400,
-        storagePrefix: 'thebe-binder-',
+        storagePrefix: 'thebe-binder',
       });
     });
     test('server settings', () => {
diff --git a/packages/core/tests/options.spec.ts b/packages/core/tests/options.spec.ts
index 0f9a9cee..5db391b8 100644
--- a/packages/core/tests/options.spec.ts
+++ b/packages/core/tests/options.spec.ts
@@ -38,7 +38,7 @@ describe('options', () => {
       expect(makeSavedSessionOptions({})).toEqual({
         enabled: true,
         maxAge: 86400,
-        storagePrefix: 'thebe-binder-',
+        storagePrefix: 'thebe-binder',
       });
     });
     test('overrides', () => {
diff --git a/packages/core/tests/url.spec.ts b/packages/core/tests/url.spec.ts
index 1630396a..b48ee9d7 100644
--- a/packages/core/tests/url.spec.ts
+++ b/packages/core/tests/url.spec.ts
@@ -1,7 +1,7 @@
 import { describe, test, expect } from 'vitest';
 import { WELL_KNOWN_REPO_PROVIDERS, makeBinderUrls } from '../src/url';
 import { makeBinderOptions } from '../src/options';
-import type { BinderOptions } from '../src/types';
+import { Config } from '../src/config';
 
 const binderUrl = 'https://binder.curvenote.dev/';
 
@@ -10,119 +10,170 @@ describe('building binder urls', () => {
     test('git', () => {
       expect(
         makeBinderUrls(
-          makeBinderOptions({ binderUrl, repoProvider: 'git' }),
+          new Config({
+            binderOptions: makeBinderOptions({ binderUrl, repoProvider: 'git' }),
+          }),
           WELL_KNOWN_REPO_PROVIDERS,
         ),
       ).toEqual({
         build: 'https://binder.curvenote.dev/build/git/executablebooks%2Fthebe-binder-base/HEAD',
         launch: 'https://binder.curvenote.dev/v2/git/executablebooks%2Fthebe-binder-base/HEAD',
+        storageKey:
+          'thebe-binder-https://binder.curvenote.dev/build/git/executablebooks%2Fthebe-binder-base/HEAD',
       });
       expect(
         makeBinderUrls(
-          makeBinderOptions({ binderUrl, repoProvider: 'git', ref: 'main' }),
+          new Config({
+            binderOptions: makeBinderOptions({ binderUrl, repoProvider: 'git', ref: 'main' }),
+          }),
           WELL_KNOWN_REPO_PROVIDERS,
         ),
       ).toEqual({
         build: 'https://binder.curvenote.dev/build/git/executablebooks%2Fthebe-binder-base/main',
         launch: 'https://binder.curvenote.dev/v2/git/executablebooks%2Fthebe-binder-base/main',
+        storageKey:
+          'thebe-binder-https://binder.curvenote.dev/build/git/executablebooks%2Fthebe-binder-base/main',
       });
     });
     test('gitlab', () => {
       expect(
         makeBinderUrls(
-          makeBinderOptions({ binderUrl, repoProvider: 'gitlab' }),
+          new Config({
+            binderOptions: makeBinderOptions({ binderUrl, repoProvider: 'gitlab' }),
+          }),
           WELL_KNOWN_REPO_PROVIDERS,
         ),
       ).toEqual({
         build: 'https://binder.curvenote.dev/build/gl/executablebooks%2Fthebe-binder-base/HEAD',
         launch: 'https://binder.curvenote.dev/v2/gl/executablebooks%2Fthebe-binder-base/HEAD',
+        storageKey:
+          'thebe-binder-https://binder.curvenote.dev/build/gl/executablebooks%2Fthebe-binder-base/HEAD',
       });
       expect(
         makeBinderUrls(
-          makeBinderOptions({ binderUrl, repoProvider: 'gitlab', ref: 'main' }),
+          new Config({
+            binderOptions: makeBinderOptions({ binderUrl, repoProvider: 'gitlab', ref: 'main' }),
+          }),
           WELL_KNOWN_REPO_PROVIDERS,
         ),
       ).toEqual({
         build: 'https://binder.curvenote.dev/build/gl/executablebooks%2Fthebe-binder-base/main',
         launch: 'https://binder.curvenote.dev/v2/gl/executablebooks%2Fthebe-binder-base/main',
+        storageKey:
+          'thebe-binder-https://binder.curvenote.dev/build/gl/executablebooks%2Fthebe-binder-base/main',
       });
     });
     test('github', () => {
       expect(
         makeBinderUrls(
-          makeBinderOptions({ binderUrl, repoProvider: 'github' }),
+          new Config({
+            binderOptions: makeBinderOptions({ binderUrl, repoProvider: 'github' }),
+          }),
           WELL_KNOWN_REPO_PROVIDERS,
         ),
       ).toEqual({
         build: 'https://binder.curvenote.dev/build/gh/executablebooks/thebe-binder-base/HEAD',
         launch: 'https://binder.curvenote.dev/v2/gh/executablebooks/thebe-binder-base/HEAD',
+        storageKey:
+          'thebe-binder-https://binder.curvenote.dev/build/gh/executablebooks/thebe-binder-base/HEAD',
       });
       expect(
         makeBinderUrls(
-          makeBinderOptions({ binderUrl, repoProvider: 'github', ref: 'main' }),
+          new Config({
+            binderOptions: makeBinderOptions({ binderUrl, repoProvider: 'github', ref: 'main' }),
+          }),
           WELL_KNOWN_REPO_PROVIDERS,
         ),
       ).toEqual({
         build: 'https://binder.curvenote.dev/build/gh/executablebooks/thebe-binder-base/main',
         launch: 'https://binder.curvenote.dev/v2/gh/executablebooks/thebe-binder-base/main',
+        storageKey:
+          'thebe-binder-https://binder.curvenote.dev/build/gh/executablebooks/thebe-binder-base/main',
       });
     });
     test('gist', () => {
       expect(
         makeBinderUrls(
-          makeBinderOptions({ binderUrl, repoProvider: 'gist' }),
+          new Config({
+            binderOptions: makeBinderOptions({ binderUrl, repoProvider: 'gist' }),
+          }),
           WELL_KNOWN_REPO_PROVIDERS,
         ),
       ).toEqual({
         build: 'https://binder.curvenote.dev/build/gist/executablebooks/thebe-binder-base/HEAD',
         launch: 'https://binder.curvenote.dev/v2/gist/executablebooks/thebe-binder-base/HEAD',
+        storageKey:
+          'thebe-binder-https://binder.curvenote.dev/build/gist/executablebooks/thebe-binder-base/HEAD',
       });
       expect(
         makeBinderUrls(
-          makeBinderOptions({ binderUrl, repoProvider: 'gist', ref: 'main' }),
+          new Config({
+            binderOptions: makeBinderOptions({ binderUrl, repoProvider: 'gist', ref: 'main' }),
+          }),
           WELL_KNOWN_REPO_PROVIDERS,
         ),
       ).toEqual({
         build: 'https://binder.curvenote.dev/build/gist/executablebooks/thebe-binder-base/main',
         launch: 'https://binder.curvenote.dev/v2/gist/executablebooks/thebe-binder-base/main',
+        storageKey:
+          'thebe-binder-https://binder.curvenote.dev/build/gist/executablebooks/thebe-binder-base/main',
       });
     });
   });
   test('unknown provider throws', () => {
     expect(() =>
       makeBinderUrls(
-        makeBinderOptions({ binderUrl, repoProvider: 'unknown' }),
+        new Config({
+          binderOptions: makeBinderOptions({ binderUrl, repoProvider: 'unknown' }),
+        }),
         WELL_KNOWN_REPO_PROVIDERS,
       ),
     ).toThrow();
   });
   describe('custom providers', () => {
     test('known custom provider - no ref', () => {
-      const opts = { binderUrl, repoProvider: 'custom', repo: 'sunshine' };
+      const binderOptions = { binderUrl, repoProvider: 'custom', repo: 'sunshine' };
+      const c = new Config({ binderOptions });
       const spec = {
         name: 'custom',
-        makeUrls: ({ repo, ref }: BinderOptions) => ({
-          build: `https://custom.host.com/build/custom/${repo}${ref ? `~~~${ref}` : ''}`,
-          launch: `https://custom.host.com/v2/custom/${repo}${ref ? `~~~${ref}` : ''}`,
+        makeUrls: (config: Config) => ({
+          build: `https://custom.host.com/build/custom/${config.binder.repo}`,
+          launch: `https://custom.host.com/v2/custom/${config.binder.repo}`,
+          storageKey: `thebe-binder-https://custom.host.com/v2/custom/${config.binder.repo}`,
         }),
       };
-      expect(makeBinderUrls(opts, [spec])).toEqual({
+      expect(makeBinderUrls(c, [spec])).toEqual({
         build: `https://custom.host.com/build/custom/sunshine`,
         launch: `https://custom.host.com/v2/custom/sunshine`,
+        storageKey: 'thebe-binder-https://custom.host.com/v2/custom/sunshine',
       });
     });
     test('known custom provider - with ref', () => {
-      const opts = { binderUrl, repoProvider: 'custom', repo: 'sunshine', ref: 'unicorns' };
+      const binderOptions = {
+        binderUrl,
+        repoProvider: 'custom',
+        repo: 'sunshine',
+        ref: 'unicorns',
+      };
+      const c = new Config({ binderOptions });
       const spec = {
         name: 'custom',
-        makeUrls: ({ repo, ref }: BinderOptions) => ({
-          build: `https://custom.host.com/build/custom/${repo}${ref ? `~~~${ref}` : ''}`,
-          launch: `https://custom.host.com/v2/custom/${repo}${ref ? `~~~${ref}` : ''}`,
+        makeUrls: (config: Config) => ({
+          build: `https://custom.host.com/build/custom/${config.binder.repo}${
+            config.binder.ref ? `~~~${config.binder.ref}` : ''
+          }`,
+          launch: `https://custom.host.com/v2/custom/${config.binder.repo}${
+            config.binder.ref ? `~~~${config.binder.ref}` : ''
+          }`,
+          storageKey: `thebe-binder-https://custom.host.com/v2/custom/${config.binder.repo}${
+            config.binder.ref ? `~~~${config.binder.ref}` : ''
+          }`,
         }),
       };
-      expect(makeBinderUrls(opts, [spec])).toEqual({
+      expect(makeBinderUrls(c, [spec])).toEqual({
         build: `https://custom.host.com/build/custom/sunshine~~~unicorns`,
         launch: `https://custom.host.com/v2/custom/sunshine~~~unicorns`,
+        storageKey: 'thebe-binder-https://custom.host.com/v2/custom/sunshine~~~unicorns',
       });
     });
   });