diff --git a/api/client/javascript/package.json b/api/client/javascript/package.json
index 41cd31a2b..68cac0fa5 100644
--- a/api/client/javascript/package.json
+++ b/api/client/javascript/package.json
@@ -50,7 +50,7 @@
     "lint": "eslint . --format=pretty",
     "format": "prettier --write .",
     "build": "duel",
-    "generate": "node --experimental-strip-types scripts/generate.ts && prettier --write src/client/schemas.d.ts",
+    "generate": "node --experimental-strip-types scripts/generate.ts && prettier --write src/client/schemas.ts",
     "pretest": "pnpm run build",
     "test": "vitest --run",
     "test:watch": "vitest --watch",
diff --git a/api/client/javascript/scripts/generate.ts b/api/client/javascript/scripts/generate.ts
index 5328e76fb..2cff4abc4 100644
--- a/api/client/javascript/scripts/generate.ts
+++ b/api/client/javascript/scripts/generate.ts
@@ -48,4 +48,4 @@ const ast = await openapiTS(schema, {
 
 const contents = astToString(ast)
 
-fs.writeFileSync('./src/client/schemas.d.ts', contents)
+fs.writeFileSync('./src/client/schemas.ts', contents)
diff --git a/api/client/javascript/src/client/apps.ts b/api/client/javascript/src/client/apps.ts
index 81a43a4fc..5cb622c84 100644
--- a/api/client/javascript/src/client/apps.ts
+++ b/api/client/javascript/src/client/apps.ts
@@ -1,4 +1,5 @@
-import { transformResponse, type RequestOptions } from './utils.js'
+import { transformResponse } from './utils.js'
+import type { RequestOptions } from './common.js'
 import type {
   AppBaseReplaceUpdate,
   CreateStripeCheckoutSessionRequest,
diff --git a/api/client/javascript/src/client/billing.ts b/api/client/javascript/src/client/billing.ts
index b949670de..7fba9f707 100644
--- a/api/client/javascript/src/client/billing.ts
+++ b/api/client/javascript/src/client/billing.ts
@@ -1,4 +1,5 @@
-import { transformResponse, type RequestOptions } from './utils.js'
+import { transformResponse } from './utils.js'
+import type { RequestOptions } from './common.js'
 import type {
   BillingProfileCreate,
   BillingProfileCustomerOverrideCreate,
@@ -11,7 +12,6 @@ import type {
   VoidInvoiceActionInput,
 } from './schemas.js'
 import type { Client } from 'openapi-fetch'
-
 /**
  * Billing
  */
diff --git a/api/client/javascript/src/client/common.ts b/api/client/javascript/src/client/common.ts
new file mode 100644
index 000000000..c2eb0c1b1
--- /dev/null
+++ b/api/client/javascript/src/client/common.ts
@@ -0,0 +1,62 @@
+import type { UnexpectedProblemResponse } from './schemas.js'
+
+/**
+ * Request options
+ */
+export type RequestOptions = Pick<RequestInit, 'signal'>
+
+/**
+ * An error that occurred during an HTTP request
+ */
+export class HTTPError extends Error {
+  name = 'HTTPError'
+
+  constructor(
+    public message: string,
+    public type: string,
+    public title: string,
+    public status: number,
+    protected __raw?: Record<string, any>
+  ) {
+    super(message)
+  }
+
+  static fromResponse(resp: {
+    response: Response
+    error?: UnexpectedProblemResponse
+  }): HTTPError {
+    if (
+      resp.response.headers.get('Content-Type') ===
+        'application/problem+json' &&
+      resp.error
+    ) {
+      return new HTTPError(
+        resp.error.detail,
+        resp.error.type,
+        resp.error.title,
+        resp.error.status ?? resp.response.status,
+        resp.error
+      )
+    }
+
+    return new HTTPError(
+      `Request failed: ${resp.response.statusText}`,
+      resp.response.statusText,
+      resp.response.statusText,
+      resp.response.status
+    )
+  }
+
+  getField(key: string) {
+    return this.__raw?.[key]
+  }
+}
+
+/**
+ * Check if an error is an HTTPError
+ * @param error - The error to check
+ * @returns Whether the error is an HTTPError
+ */
+export function isHTTPError(error: unknown): error is HTTPError {
+  return error instanceof HTTPError
+}
diff --git a/api/client/javascript/src/client/customers.ts b/api/client/javascript/src/client/customers.ts
index 086afe5ab..09de55322 100644
--- a/api/client/javascript/src/client/customers.ts
+++ b/api/client/javascript/src/client/customers.ts
@@ -1,4 +1,5 @@
-import { transformResponse, type RequestOptions } from './utils.js'
+import { transformResponse } from './utils.js'
+import type { RequestOptions } from './common.js'
 import type {
   CustomerAppData,
   CustomerCreate,
diff --git a/api/client/javascript/src/client/entitlements.ts b/api/client/javascript/src/client/entitlements.ts
index 55db85601..f78728928 100644
--- a/api/client/javascript/src/client/entitlements.ts
+++ b/api/client/javascript/src/client/entitlements.ts
@@ -1,4 +1,5 @@
-import { transformResponse, type RequestOptions } from './utils.js'
+import { transformResponse } from './utils.js'
+import type { RequestOptions } from './common.js'
 import type {
   EntitlementCreateInputs,
   EntitlementGrantCreateInput,
diff --git a/api/client/javascript/src/client/events.spec.ts b/api/client/javascript/src/client/events.spec.ts
index 312518d3a..fffa8f628 100644
--- a/api/client/javascript/src/client/events.spec.ts
+++ b/api/client/javascript/src/client/events.spec.ts
@@ -61,7 +61,7 @@ describe('Events', () => {
       }
     )
     const resp = await client.events.ingest(event)
-    expect(resp.data).toBeUndefined()
+    expect(resp).toBeUndefined()
     expect(fetchMock.callHistory.done(task.name)).toBeTruthy()
   })
 
@@ -104,7 +104,7 @@ describe('Events', () => {
       }
     )
     const resp = await client.events.list(query)
-    expect(resp.data).toEqual(respBody)
+    expect(resp).toEqual(respBody)
     expect(fetchMock.callHistory.done(task.name)).toBeTruthy()
   })
 })
diff --git a/api/client/javascript/src/client/events.ts b/api/client/javascript/src/client/events.ts
index 8d93bdf53..a8e1a3ef1 100644
--- a/api/client/javascript/src/client/events.ts
+++ b/api/client/javascript/src/client/events.ts
@@ -1,5 +1,6 @@
 import crypto from 'crypto'
-import { transformResponse, type RequestOptions } from './utils.js'
+import { transformResponse } from './utils.js'
+import type { RequestOptions } from './common.js'
 import type { operations, paths, Event } from './schemas.js'
 import type { Client } from 'openapi-fetch'
 
diff --git a/api/client/javascript/src/client/features.ts b/api/client/javascript/src/client/features.ts
index 47979246e..4dda8166e 100644
--- a/api/client/javascript/src/client/features.ts
+++ b/api/client/javascript/src/client/features.ts
@@ -1,4 +1,5 @@
-import { transformResponse, type RequestOptions } from './utils.js'
+import { transformResponse } from './utils.js'
+import type { RequestOptions } from './common.js'
 import type { FeatureCreateInputs, operations, paths } from './schemas.js'
 import type { Client } from 'openapi-fetch'
 
diff --git a/api/client/javascript/src/client/index.ts b/api/client/javascript/src/client/index.ts
index c8533b2c6..97917d9b1 100644
--- a/api/client/javascript/src/client/index.ts
+++ b/api/client/javascript/src/client/index.ts
@@ -18,7 +18,8 @@ import { Subscriptions } from './subscriptions.js'
 import { encodeDates } from './utils.js'
 import type { paths } from './schemas.js'
 
-export type * from './schemas.js'
+export * from './schemas.js'
+export * from './common.js'
 
 /**
  * OpenMeter Config
diff --git a/api/client/javascript/src/client/meters.ts b/api/client/javascript/src/client/meters.ts
index 5e3886dc0..920daa3c6 100644
--- a/api/client/javascript/src/client/meters.ts
+++ b/api/client/javascript/src/client/meters.ts
@@ -1,4 +1,5 @@
-import { transformResponse, type RequestOptions } from './utils.js'
+import { transformResponse } from './utils.js'
+import type { RequestOptions } from './common.js'
 import type { MeterCreate, operations, paths } from './schemas.js'
 import type { Client } from 'openapi-fetch'
 
diff --git a/api/client/javascript/src/client/notifications.ts b/api/client/javascript/src/client/notifications.ts
index ebbdfa215..946827d62 100644
--- a/api/client/javascript/src/client/notifications.ts
+++ b/api/client/javascript/src/client/notifications.ts
@@ -1,4 +1,5 @@
-import { transformResponse, type RequestOptions } from './utils.js'
+import { transformResponse } from './utils.js'
+import type { RequestOptions } from './common.js'
 import type {
   NotificationChannel,
   NotificationRuleCreateRequest,
diff --git a/api/client/javascript/src/client/plans.ts b/api/client/javascript/src/client/plans.ts
index 2a0e8ef98..b37481ece 100644
--- a/api/client/javascript/src/client/plans.ts
+++ b/api/client/javascript/src/client/plans.ts
@@ -1,4 +1,5 @@
-import { transformResponse, type RequestOptions } from './utils.js'
+import { transformResponse } from './utils.js'
+import type { RequestOptions } from './common.js'
 import type {
   operations,
   paths,
diff --git a/api/client/javascript/src/client/portal.ts b/api/client/javascript/src/client/portal.ts
index a35b34cdb..0a3eb5351 100644
--- a/api/client/javascript/src/client/portal.ts
+++ b/api/client/javascript/src/client/portal.ts
@@ -1,4 +1,5 @@
-import { transformResponse, type RequestOptions } from './utils.js'
+import { transformResponse } from './utils.js'
+import type { RequestOptions } from './common.js'
 import type { operations, paths, PortalToken } from './schemas.js'
 import type { Client } from 'openapi-fetch'
 
diff --git a/api/client/javascript/src/client/schemas.d.ts b/api/client/javascript/src/client/schemas.ts
similarity index 100%
rename from api/client/javascript/src/client/schemas.d.ts
rename to api/client/javascript/src/client/schemas.ts
diff --git a/api/client/javascript/src/client/subjects.ts b/api/client/javascript/src/client/subjects.ts
index 26d32ab3e..5360cc6e8 100644
--- a/api/client/javascript/src/client/subjects.ts
+++ b/api/client/javascript/src/client/subjects.ts
@@ -1,4 +1,5 @@
-import { transformResponse, type RequestOptions } from './utils.js'
+import { transformResponse } from './utils.js'
+import type { RequestOptions } from './common.js'
 import type { operations, paths, SubjectUpsert } from './schemas.js'
 import type { Client } from 'openapi-fetch'
 
diff --git a/api/client/javascript/src/client/subscriptions.ts b/api/client/javascript/src/client/subscriptions.ts
index 8e03848ba..ab732e59b 100644
--- a/api/client/javascript/src/client/subscriptions.ts
+++ b/api/client/javascript/src/client/subscriptions.ts
@@ -1,4 +1,5 @@
-import { transformResponse, type RequestOptions } from './utils.js'
+import { transformResponse } from './utils.js'
+import type { RequestOptions } from './common.js'
 import type {
   operations,
   paths,
diff --git a/api/client/javascript/src/client/utils.ts b/api/client/javascript/src/client/utils.ts
index e58c963bd..bbc1399f3 100644
--- a/api/client/javascript/src/client/utils.ts
+++ b/api/client/javascript/src/client/utils.ts
@@ -1,4 +1,4 @@
-import type { UnexpectedProblemResponse } from './schemas.js'
+import { HTTPError } from './common.js'
 import type { FetchResponse, ParseAsResponse } from 'openapi-fetch'
 import type {
   MediaType,
@@ -6,55 +6,12 @@ import type {
   SuccessResponse,
 } from 'openapi-typescript-helpers'
 
-// Add more options as needed: 'headers' | 'credentials' | 'mode' | 'referrer' | 'referrerPolicy'
-export type RequestOptions = Pick<RequestInit, 'signal'>
-
-export class Problem extends Error {
-  name = 'Problem'
-
-  constructor(
-    public message: string,
-    public type: string,
-    public title: string,
-    public status: number,
-
-    protected __raw?: Record<string, any>
-  ) {
-    super(message)
-  }
-
-  static fromResponse(resp: {
-    response: Response
-    error?: UnexpectedProblemResponse
-  }): Problem {
-    if (
-      resp.response.headers.get('Content-Type') ===
-        'application/problem+json' &&
-      resp.error
-    ) {
-      return new Problem(
-        resp.error.detail,
-        resp.error.type,
-        resp.error.title,
-        resp.error.status ?? resp.response.status,
-        resp.error
-      )
-    }
-
-    return new Problem(
-      `Request failed: ${resp.response.statusText}`,
-      resp.response.statusText,
-      resp.response.statusText,
-      resp.response.status
-    )
-  }
-
-  getField(key: string) {
-    return this.__raw?.[key]
-  }
-}
-
-// Implementation
+/**
+ * Transform a response from the API
+ * @param resp - The response to transform
+ * @throws HTTPError if the response is an error
+ * @returns The transformed response
+ */
 export function transformResponse<
   T extends Record<string | number, any>,
   Options,
@@ -62,24 +19,11 @@ export function transformResponse<
 >(
   resp: FetchResponse<T, Options, Media>
 ):
-  | {
-      data: ParseAsResponse<
-        SuccessResponse<ResponseObjectMap<T>, Media>,
-        Options
-      >
-      error?: never
-      response: Response
-    }
-  | {
-      data?: never
-      error: Problem
-      response: Response
-    } {
+  | ParseAsResponse<SuccessResponse<ResponseObjectMap<T>, Media>, Options>
+  | never {
   // Handle errors
   if (resp.error || resp.response.status >= 400) {
-    const error = Problem.fromResponse(resp)
-
-    return { error, response: resp.response }
+    throw HTTPError.fromResponse(resp)
   }
 
   // Decode dates
@@ -87,7 +31,7 @@ export function transformResponse<
     resp.data = decodeDates(resp.data)
   }
 
-  return { data: resp.data!, response: resp.response }
+  return resp.data!
 }
 
 const ISODateFormat =
diff --git a/api/client/javascript/src/portal/index.ts b/api/client/javascript/src/portal/index.ts
index 02633c3b6..06cf57118 100644
--- a/api/client/javascript/src/portal/index.ts
+++ b/api/client/javascript/src/portal/index.ts
@@ -1,12 +1,10 @@
 import createClient from 'openapi-fetch'
 import { createQuerySerializer } from 'openapi-fetch/dist/cjs/index.cjs'
 import { encodeDates, transformResponse } from '../client/utils.js'
+import type { RequestOptions } from '../client/common.js'
 import type { paths } from '../client/schemas.js'
-import type { RequestOptions } from '../client/utils.js'
 import type { Client, ClientOptions } from 'openapi-fetch'
 
-export type { RequestOptions } from '../client/utils.js'
-
 /**
  * Portal Config
  */