diff --git a/src/view/com/composer/select-language/SuggestedLanguage.tsx b/src/view/com/composer/select-language/SuggestedLanguage.tsx
index ab731cda2..04fad82a5 100644
--- a/src/view/com/composer/select-language/SuggestedLanguage.tsx
+++ b/src/view/com/composer/select-language/SuggestedLanguage.tsx
@@ -2,10 +2,6 @@ import {useEffect, useMemo, useRef, useState} from 'react'
 import {Platform, Text as RNText, View} from 'react-native'
 import {RichText} from '@atproto/api'
 import {parseLanguageString} from '@atproto/syntax'
-import {
-  guessLanguageAsync,
-  type LanguageResult,
-} from '@bsky.app/expo-guess-language'
 import {Trans, useLingui} from '@lingui/react/macro'
 import debounce from 'lodash.debounce'
 
@@ -22,6 +18,7 @@ import {TimesLarge_Stroke2_Corner0_Rounded as XIcon} from '#/components/icons/Ti
 import {Text} from '#/components/Typography'
 import {useAnalytics} from '#/analytics'
 import {IS_WEB} from '#/env'
+import {guessLanguageAsync, type LanguageResult} from './languageDetection'
 
 type LanguageDetectionPerLanguageConfig = {
   acceptanceThreshold?: number
diff --git a/src/view/com/composer/select-language/languageDetection.ts b/src/view/com/composer/select-language/languageDetection.ts
new file mode 100644
index 000000000..6b993c1a2
--- /dev/null
+++ b/src/view/com/composer/select-language/languageDetection.ts
@@ -0,0 +1,4 @@
+export {
+  guessLanguageAsync,
+  type LanguageResult,
+} from '@bsky.app/expo-guess-language'
diff --git a/src/view/com/composer/select-language/languageDetection.web.ts b/src/view/com/composer/select-language/languageDetection.web.ts
new file mode 100644
index 000000000..1a21fe8bd
--- /dev/null
+++ b/src/view/com/composer/select-language/languageDetection.web.ts
@@ -0,0 +1,70 @@
+import {type LanguageResult} from '@bsky.app/expo-guess-language'
+
+type WorkerResponse =
+  | {id: number; results: LanguageResult[]}
+  | {id: number; error: string}
+
+type PendingRequest = {
+  resolve: (results: LanguageResult[]) => void
+  reject: (error: Error) => void
+}
+
+let nextRequestId = 0
+let languageWorker: Worker | undefined
+const pendingRequests = new Map<number, PendingRequest>()
+
+function getLanguageWorker(): Worker {
+  if (languageWorker) {
+    return languageWorker
+  }
+
+  languageWorker = new Worker(
+    new URL('./languageDetection.worker.ts', import.meta.url),
+    {type: 'module'},
+  )
+  languageWorker.onmessage = (event: MessageEvent<WorkerResponse>) => {
+    const request = pendingRequests.get(event.data.id)
+    if (!request) {
+      return
+    }
+    pendingRequests.delete(event.data.id)
+
+    if ('error' in event.data) {
+      request.reject(new Error(event.data.error))
+    } else {
+      request.resolve(event.data.results)
+    }
+  }
+  languageWorker.onerror = event => {
+    const error = new Error(event.message || 'Language detection worker failed')
+    for (const request of pendingRequests.values()) {
+      request.reject(error)
+    }
+    pendingRequests.clear()
+    languageWorker?.terminate()
+    languageWorker = undefined
+  }
+
+  return languageWorker
+}
+
+/**
+ * Runs web language inference away from the UI thread. The web implementation
+ * of expo-guess-language uses lande synchronously even though its public API
+ * returns a Promise, so calling it on the main thread can delay composer input
+ * on slower devices.
+ */
+export function guessLanguageAsync(text: string): Promise<LanguageResult[]> {
+  const id = ++nextRequestId
+  return new Promise((resolve, reject) => {
+    pendingRequests.set(id, {resolve, reject})
+    try {
+      getLanguageWorker().postMessage({id, text})
+    } catch (error) {
+      pendingRequests.delete(id)
+      reject(error instanceof Error ? error : new Error(String(error)))
+    }
+  })
+}
+
+export {type LanguageResult}
diff --git a/src/view/com/composer/select-language/languageDetection.worker.ts b/src/view/com/composer/select-language/languageDetection.worker.ts
new file mode 100644
index 000000000..f1c0e374a
--- /dev/null
+++ b/src/view/com/composer/select-language/languageDetection.worker.ts
@@ -0,0 +1,14 @@
+import {guessLanguageAsync} from '@bsky.app/expo-guess-language'
+
+self.onmessage = async (event: MessageEvent<{id: number; text: string}>) => {
+  const {id, text} = event.data
+  try {
+    const results = await guessLanguageAsync(text)
+    self.postMessage({id, results})
+  } catch (error) {
+    self.postMessage({
+      id,
+      error: error instanceof Error ? error.message : String(error),
+    })
+  }
+}
diff --git a/src/view/com/composer/text-input/TextInput.web.tsx b/src/view/com/composer/text-input/TextInput.web.tsx
index 8715eb9cd..db31824ab 100644
--- a/src/view/com/composer/text-input/TextInput.web.tsx
+++ b/src/view/com/composer/text-input/TextInput.web.tsx
@@ -1,4 +1,5 @@
 import {
+  startTransition,
   useCallback,
   useEffect,
   useImperativeHandle,
@@ -385,7 +386,17 @@ export function TextInput({
           )
         }
 
-        setRichText(newRt)
+        /*
+         * TipTap owns the editable DOM, so its transaction has already made
+         * the new character visible. The composer state update can re-render
+         * most of the sheet (counter, controls, embeds, etc.), which is not
+         * urgent and can be expensive on slower browsers. Marking it as a
+         * transition lets React yield to the browser so the editor paints the
+         * keystroke before doing that work.
+         */
+        startTransition(() => {
+          setRichText(newRt)
+        })
 
         const nextDetectedUris = new Map<string, LinkFacetMatch>()
         if (newRt.facets) {