diff --git a/.env.example b/.env.example
index 324a8f4..8357a18 100644
--- a/.env.example
+++ b/.env.example
@@ -43,8 +43,10 @@
 # Destination to redirect blocked requests to.
 # BLOCK_REDIRECT="https://roblox.com/"
 
-# Whether to reject requests containing disallowed content.
-# REJECT_DISALLOWED=false
+# Comma-separated list of phrases that will be rejected. Only whole words are matched.
+# Surround phrases with quotes if they contain commas.
+# Avoid short or common phrases as this tests the entire prompt.
+# REJECT_PHRASES="phrase one,phrase two,"phrase three, which has a comma",phrase four"
 # Message to show when requests are rejected.
 # REJECT_MESSAGE="This content violates /aicg/'s acceptable use policy."
 
diff --git a/src/config.ts b/src/config.ts
index 3d4ccda..72f555b 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -95,10 +95,10 @@ type Config = {
   maxOutputTokensOpenAI: number;
   /** For Anthropic, the maximum number of sampled tokens a user can request. */
   maxOutputTokensAnthropic: number;
-  /** Whether requests containing disallowed characters should be rejected. */
-  rejectDisallowed?: boolean;
+  /** Whether requests containing the following phrases should be rejected. */
+  rejectPhrases: string[];
   /** Message to return when rejecting requests. */
-  rejectMessage?: string;
+  rejectMessage: string;
   /** Verbosity level of diagnostic logging. */
   logLevel: "trace" | "debug" | "info" | "warn" | "error";
   /**
@@ -203,7 +203,7 @@ export const config: Config = {
     "bison",
     "aws-claude",
   ]),
-  rejectDisallowed: getEnvWithDefault("REJECT_DISALLOWED", false),
+  rejectPhrases: parseCsv(getEnvWithDefault("REJECT_PHRASES", "")),
   rejectMessage: getEnvWithDefault(
     "REJECT_MESSAGE",
     "This content violates /aicg/'s acceptable use policy."
@@ -321,6 +321,7 @@ export const OMITTED_KEYS: (keyof Config)[] = [
   "proxyKey",
   "adminKey",
   "checkKeys",
+  "rejectPhrases",
   "showTokenCosts",
   "googleSheetsKey",
   "firebaseKey",
@@ -421,3 +422,11 @@ export function getFirebaseApp(): firebase.app.App {
   }
   return firebaseApp;
 }
+
+function parseCsv(val: string): string[] {
+  if (!val) return [];
+
+  const regex = /(".*?"|[^",]+)(?=\s*,|\s*$)/g;
+  const matches = val.match(regex) || [];
+  return matches.map(item => item.replace(/^"|"$/g, '').trim());
+}
diff --git a/src/proxy/anthropic.ts b/src/proxy/anthropic.ts
index 6365fda..98cc98b 100644
--- a/src/proxy/anthropic.ts
+++ b/src/proxy/anthropic.ts
@@ -12,7 +12,6 @@ import {
   blockZoomerOrigins,
   createPreprocessorMiddleware,
   finalizeBody,
-  languageFilter,
   stripHeaders,
   createOnProxyReqHandler,
 } from "./middleware/request";
@@ -142,7 +141,6 @@ const anthropicProxy = createQueueMiddleware({
           applyQuotaLimits,
           addKey,
           addAnthropicPreamble,
-          languageFilter,
           blockZoomerOrigins,
           stripHeaders,
           finalizeBody,
diff --git a/src/proxy/aws.ts b/src/proxy/aws.ts
index e3318d6..c80aa6a 100644
--- a/src/proxy/aws.ts
+++ b/src/proxy/aws.ts
@@ -13,7 +13,6 @@ import {
   signAwsRequest,
   finalizeAwsRequest,
   createOnProxyReqHandler,
-  languageFilter,
   blockZoomerOrigins,
 } from "./middleware/request";
 import {
@@ -134,7 +133,6 @@ const awsProxy = createQueueMiddleware({
       proxyReq: createOnProxyReqHandler({
         pipeline: [
           applyQuotaLimits,
-          languageFilter,
           blockZoomerOrigins,
           stripHeaders,
           finalizeAwsRequest,
diff --git a/src/proxy/middleware/common.ts b/src/proxy/middleware/common.ts
index 3afff87..99f8281 100644
--- a/src/proxy/middleware/common.ts
+++ b/src/proxy/middleware/common.ts
@@ -90,7 +90,7 @@ function classifyError(err: Error): {
 } & Record<string, any> {
   const defaultError = {
     status: 500,
-    userMessage: `Reverse proxy encountered an unexpected error. (${err.message})`,
+    userMessage: `Reverse proxy error: ${err.message}`,
     type: "proxy_internal_error",
     stack: err.stack,
   };
diff --git a/src/proxy/middleware/request/index.ts b/src/proxy/middleware/request/index.ts
index 2b39ab7..565b9ac 100644
--- a/src/proxy/middleware/request/index.ts
+++ b/src/proxy/middleware/request/index.ts
@@ -12,6 +12,7 @@ export {
 export { applyQuotaLimits } from "./apply-quota-limits";
 export { validateContextSize } from "./validate-context-size";
 export { countPromptTokens } from "./count-prompt-tokens";
+export { languageFilter } from "./language-filter";
 export { setApiFormat } from "./set-api-format";
 export { signAwsRequest } from "./sign-aws-request";
 export { transformOutboundPayload } from "./transform-outbound-payload";
@@ -22,7 +23,6 @@ export { addAnthropicPreamble } from "./add-anthropic-preamble";
 export { blockZoomerOrigins } from "./block-zoomer-origins";
 export { finalizeBody } from "./finalize-body";
 export { finalizeAwsRequest } from "./finalize-aws-request";
-export { languageFilter } from "./language-filter";
 export { limitCompletions } from "./limit-completions";
 export { stripHeaders } from "./strip-headers";
 
diff --git a/src/proxy/middleware/request/language-filter.ts b/src/proxy/middleware/request/language-filter.ts
index 947985e..4699b9e 100644
--- a/src/proxy/middleware/request/language-filter.ts
+++ b/src/proxy/middleware/request/language-filter.ts
@@ -1,38 +1,49 @@
 import { Request } from "express";
 import { config } from "../../../config";
-import { logger } from "../../../logger";
 import { assertNever } from "../../../shared/utils";
-import { isCompletionRequest } from "../common";
-import { ProxyRequestMiddleware } from ".";
+import { RequestPreprocessor } from ".";
+import { UserInputError } from "../../../shared/errors";
 
-const DISALLOWED_REGEX =
-  /[\u2E80-\u2E99\u2E9B-\u2EF3\u2F00-\u2FD5\u3005\u3007\u3021-\u3029\u3038-\u303B\u3400-\u4DB5\u4E00-\u9FD5\uF900-\uFA6D\uFA70-\uFAD9]/;
+const rejectedClients = new Map<string, number>();
 
-// Our shitty free-tier VMs will fall over if we test every single character in
-// each 15k character request ten times a second. So we'll just sample 20% of
-// the characters and hope that's enough.
-const containsDisallowedCharacters = (text: string) => {
-  const sampleSize = Math.ceil(text.length * 0.2);
-  const sample = text
-    .split("")
-    .sort(() => 0.5 - Math.random())
-    .slice(0, sampleSize)
-    .join("");
-  return DISALLOWED_REGEX.test(sample);
-};
+console.log(config.rejectPhrases);
 
-/** Block requests containing too many disallowed characters. */
-export const languageFilter: ProxyRequestMiddleware = (_proxyReq, req) => {
-  if (!config.rejectDisallowed) {
-    return;
-  }
-
-  if (isCompletionRequest(req)) {
-    const combinedText = getPromptFromRequest(req);
-    if (containsDisallowedCharacters(combinedText)) {
-      logger.warn(`Blocked request containing bad characters`);
-      _proxyReq.destroy(new Error(config.rejectMessage));
+setInterval(() => {
+  rejectedClients.forEach((count, ip) => {
+    if (count > 0) {
+      rejectedClients.set(ip, Math.floor(count / 2));
+    } else {
+      rejectedClients.delete(ip);
     }
+  });
+}, 30000);
+
+/**
+ * Block requests containing blacklisted phrases. Repeated rejections from the
+ * same IP address will be throttled.
+ */
+export const languageFilter: RequestPreprocessor = async (req) => {
+  if (!config.rejectPhrases.length) return;
+
+  const prompt = getPromptFromRequest(req);
+  const match = config.rejectPhrases.find((phrase) =>
+    prompt.match(new RegExp(phrase, "i"))
+  );
+
+  if (match) {
+    const ip = req.ip;
+    const rejections = (rejectedClients.get(req.ip) || 0) + 1;
+    const delay = Math.min(60000, Math.pow(2, rejections - 1) * 1000);
+    rejectedClients.set(ip, rejections);
+    req.log.warn(
+      { match, ip, rejections, delay },
+      "Prompt contains rejected phrase"
+    );
+    await new Promise((resolve) => {
+      req.res!.once("close", resolve);
+      setTimeout(resolve, delay);
+    });
+    throw new UserInputError(config.rejectMessage);
   }
 };
 
@@ -44,8 +55,10 @@ function getPromptFromRequest(req: Request) {
       return body.prompt;
     case "openai":
       return body.messages
-        .map((m: { content: string }) => m.content)
-        .join("\n");
+        .map(
+          (m: { content: string; role: string }) => `${m.role}: ${m.content}`
+        )
+        .join("\n\n");
     case "openai-text":
       return body.prompt;
     case "google-palm":
diff --git a/src/proxy/middleware/request/preprocess.ts b/src/proxy/middleware/request/preprocess.ts
index 347bb14..be515a8 100644
--- a/src/proxy/middleware/request/preprocess.ts
+++ b/src/proxy/middleware/request/preprocess.ts
@@ -7,6 +7,7 @@ import {
   countPromptTokens,
   setApiFormat,
   transformOutboundPayload,
+  languageFilter,
 } from ".";
 import { ZodIssue } from "zod";
 
@@ -38,6 +39,7 @@ export const createPreprocessorMiddleware = (
     ...(beforeTransform ?? []),
     transformOutboundPayload,
     countPromptTokens,
+    languageFilter,
     ...(afterTransform ?? []),
     validateContextSize,
   ];
@@ -81,7 +83,11 @@ async function executePreprocessors(
     // stream yet as that is typically done later by the request queue. We'll
     // do that here and then call classifyErrorAndSend to use the streaming
     // error handler.
-    initializeSseStream(res);
+    const { stream } = req.body;
+    const isStreaming = stream === "true" || stream === true;
+    if (isStreaming && !res.headersSent) {
+      initializeSseStream(res);
+    }
     classifyErrorAndSend(error as Error, req, res);
   }
 }
diff --git a/src/proxy/openai.ts b/src/proxy/openai.ts
index e3a45fa..68f78ce 100644
--- a/src/proxy/openai.ts
+++ b/src/proxy/openai.ts
@@ -21,7 +21,6 @@ import {
   createPreprocessorMiddleware,
   finalizeBody,
   forceModel,
-  languageFilter,
   limitCompletions,
   stripHeaders,
   createOnProxyReqHandler,
@@ -175,7 +174,6 @@ const openaiProxy = createQueueMiddleware({
         pipeline: [
           applyQuotaLimits,
           addKey,
-          languageFilter,
           limitCompletions,
           blockZoomerOrigins,
           stripHeaders,
diff --git a/src/proxy/palm.ts b/src/proxy/palm.ts
index 1f3887b..0c9d67b 100644
--- a/src/proxy/palm.ts
+++ b/src/proxy/palm.ts
@@ -15,7 +15,6 @@ import {
   createPreprocessorMiddleware,
   finalizeBody,
   forceModel,
-  languageFilter,
   stripHeaders,
 } from "./middleware/request";
 import {
@@ -155,7 +154,6 @@ const googlePalmProxy = createQueueMiddleware({
         pipeline: [
           applyQuotaLimits,
           addKey,
-          languageFilter,
           blockZoomerOrigins,
           stripHeaders,
           finalizeBody,