diff --git a/examples/with-langgraph/components/tools/purchase-stock/PurchaseStockTool.tsx b/examples/with-langgraph/components/tools/purchase-stock/PurchaseStockTool.tsx
index 87a8c0dda..000d79416 100644
--- a/examples/with-langgraph/components/tools/purchase-stock/PurchaseStockTool.tsx
+++ b/examples/with-langgraph/components/tools/purchase-stock/PurchaseStockTool.tsx
@@ -2,7 +2,7 @@
 
 import { TransactionConfirmationPending } from "./transaction-confirmation-pending";
 import { TransactionConfirmationFinal } from "./transaction-confirmation-final";
-import { makeAssistantToolUI, useThreadStore } from "@assistant-ui/react";
+import { makeAssistantToolUI, useThreadRuntime } from "@assistant-ui/react";
 import { updateState } from "@/lib/chatApi";
 
 type PurchaseStockArgs = {
@@ -32,9 +32,9 @@ export const PurchaseStockTool = makeAssistantToolUI<PurchaseStockArgs, string>(
         ? (JSON.parse(result) as { transactionId: string })
         : undefined;
 
-      const threadStore = useThreadStore();
+      const threadRuntime = useThreadRuntime();
       const handleConfirm = async () => {
-        await updateState(threadStore.getState().threadId, {
+        await updateState(threadRuntime.getState().threadId, {
           newState: CONFIRM_PURCHASE,
           asNode: PREPARE_PURCHASE_DETAILS_NODE,
         });
diff --git a/packages/react/src/api/ThreadRuntime.ts b/packages/react/src/api/ThreadRuntime.ts
index 372100c0a..03e1a78d5 100644
--- a/packages/react/src/api/ThreadRuntime.ts
+++ b/packages/react/src/api/ThreadRuntime.ts
@@ -186,12 +186,12 @@ export type ThreadRuntime = {
   submitFeedback: (feedback: SubmitFeedbackOptions) => void;
 
   /**
-   * @deprecated Use `getMesssageById(id).getMessageByIndex(idx).composer` instead. This will be removed in 0.6.0.
+   * @deprecated Use `getMesssageById(id).composer` instead. This will be removed in 0.6.0.
    */
   getEditComposer: (messageId: string) => ComposerRuntimeCore | undefined;
 
   /**
-   * @deprecated Use `getMesssageById(id).getMessageByIndex(idx).composer.beginEdit()` instead. This will be removed in 0.6.0.
+   * @deprecated Use `getMesssageById(id).composer.beginEdit()` instead. This will be removed in 0.6.0.
    */
   beginEdit: (messageId: string) => void;
 };
diff --git a/packages/react/src/primitive-hooks/actionBar/useActionBarCopy.tsx b/packages/react/src/primitive-hooks/actionBar/useActionBarCopy.tsx
index d58acb238..d29f927dc 100644
--- a/packages/react/src/primitive-hooks/actionBar/useActionBarCopy.tsx
+++ b/packages/react/src/primitive-hooks/actionBar/useActionBarCopy.tsx
@@ -1,11 +1,11 @@
 import { useCallback } from "react";
 import {
-  useEditComposerStore,
-  useMessageStore,
+  useMessageRuntime,
   useMessageUtilsStore,
 } from "../../context/react/MessageContext";
 import { useCombinedStore } from "../../utils/combined/useCombinedStore";
 import { getThreadMessageText } from "../../utils/getThreadMessageText";
+import { useComposerRuntime } from "../../context";
 
 export type UseActionBarCopyProps = {
   copiedDuration?: number | undefined;
@@ -14,11 +14,11 @@ export type UseActionBarCopyProps = {
 export const useActionBarCopy = ({
   copiedDuration = 3000,
 }: UseActionBarCopyProps = {}) => {
-  const messageStore = useMessageStore();
+  const messageRuntime = useMessageRuntime();
+  const composerRuntime = useComposerRuntime();
   const messageUtilsStore = useMessageUtilsStore();
-  const editComposerStore = useEditComposerStore();
   const hasCopyableContent = useCombinedStore(
-    [messageStore, editComposerStore],
+    [messageRuntime, composerRuntime],
     (message, c) => {
       return (
         !c.isEditing &&
@@ -29,9 +29,9 @@ export const useActionBarCopy = ({
   );
 
   const callback = useCallback(() => {
-    const message = messageStore.getState();
+    const message = messageRuntime.getState();
     const { setIsCopied } = messageUtilsStore.getState();
-    const { isEditing, text: composerValue } = editComposerStore.getState();
+    const { isEditing, text: composerValue } = composerRuntime.getState();
 
     const valueToCopy = isEditing
       ? composerValue
@@ -41,7 +41,7 @@ export const useActionBarCopy = ({
       setIsCopied(true);
       setTimeout(() => setIsCopied(false), copiedDuration);
     });
-  }, [messageStore, messageUtilsStore, editComposerStore, copiedDuration]);
+  }, [messageRuntime, messageUtilsStore, composerRuntime, copiedDuration]);
 
   if (!hasCopyableContent) return null;
   return callback;
diff --git a/packages/react/src/primitive-hooks/composer/useComposerCancel.tsx b/packages/react/src/primitive-hooks/composer/useComposerCancel.tsx
index 8dcc731ae..e418ebfa3 100644
--- a/packages/react/src/primitive-hooks/composer/useComposerCancel.tsx
+++ b/packages/react/src/primitive-hooks/composer/useComposerCancel.tsx
@@ -1,14 +1,13 @@
 import { useCallback } from "react";
-import { useComposer, useComposerStore } from "../../context";
+import { useComposer, useComposerRuntime } from "../../context";
 
 export const useComposerCancel = () => {
-  const composerStore = useComposerStore();
+  const composerRuntime = useComposerRuntime();
   const disabled = useComposer((c) => !c.canCancel);
 
   const callback = useCallback(() => {
-    const { cancel } = composerStore.getState();
-    cancel();
-  }, [composerStore]);
+    composerRuntime.cancel();
+  }, [composerRuntime]);
 
   if (disabled) return null;
   return callback;
diff --git a/packages/react/src/primitive-hooks/message/useMessageIf.tsx b/packages/react/src/primitive-hooks/message/useMessageIf.tsx
index 3229777d8..bc2c4bbc4 100644
--- a/packages/react/src/primitive-hooks/message/useMessageIf.tsx
+++ b/packages/react/src/primitive-hooks/message/useMessageIf.tsx
@@ -1,6 +1,6 @@
 "use client";
 import {
-  useMessageStore,
+  useMessageRuntime,
   useMessageUtilsStore,
 } from "../../context/react/MessageContext";
 import type { RequireAtLeastOne } from "../../utils/RequireAtLeastOne";
@@ -21,11 +21,11 @@ type MessageIfFilters = {
 export type UseMessageIfProps = RequireAtLeastOne<MessageIfFilters>;
 
 export const useMessageIf = (props: UseMessageIfProps) => {
-  const messageStore = useMessageStore();
+  const messageRuntime = useMessageRuntime();
   const messageUtilsStore = useMessageUtilsStore();
 
   return useCombinedStore(
-    [messageStore, messageUtilsStore],
+    [messageRuntime, messageUtilsStore],
     (
       {
         role,
diff --git a/packages/react/src/primitive-hooks/thread/useThreadSuggestion.tsx b/packages/react/src/primitive-hooks/thread/useThreadSuggestion.tsx
index fde61526b..9abd4f9da 100644
--- a/packages/react/src/primitive-hooks/thread/useThreadSuggestion.tsx
+++ b/packages/react/src/primitive-hooks/thread/useThreadSuggestion.tsx
@@ -1,7 +1,6 @@
 import { useCallback } from "react";
-import { useThread, useThreadStore } from "../../context";
-import { useAppendMessage } from "../../hooks";
-import { useThreadComposerStore } from "../../context/react/ThreadContext";
+import { useThread } from "../../context";
+import { useThreadRuntime } from "../../context/react/ThreadContext";
 
 export type UseApplyThreadSuggestionProps = {
   prompt: string;
@@ -13,21 +12,17 @@ export const useThreadSuggestion = ({
   prompt,
   autoSend,
 }: UseApplyThreadSuggestionProps) => {
-  const threadStore = useThreadStore();
-  const composerStore = useThreadComposerStore();
+  const threadRuntime = useThreadRuntime();
 
-  const append = useAppendMessage();
   const disabled = useThread((t) => t.isDisabled);
   const callback = useCallback(() => {
-    const thread = threadStore.getState();
-    const composer = composerStore.getState();
-    if (autoSend && !thread.isRunning) {
-      append(prompt);
-      composer.setText("");
+    if (autoSend && !threadRuntime.getState().isRunning) {
+      threadRuntime.append(prompt);
+      threadRuntime.composer.setText("");
     } else {
-      composer.setText(prompt);
+      threadRuntime.composer.setText(prompt);
     }
-  }, [threadStore, composerStore, autoSend, append, prompt]);
+  }, [threadRuntime, autoSend, prompt]);
 
   if (disabled) return null;
   return callback;
diff --git a/packages/react/src/primitives/actionBar/useActionBarFloatStatus.tsx b/packages/react/src/primitives/actionBar/useActionBarFloatStatus.tsx
index c08c71084..7479643d9 100644
--- a/packages/react/src/primitives/actionBar/useActionBarFloatStatus.tsx
+++ b/packages/react/src/primitives/actionBar/useActionBarFloatStatus.tsx
@@ -1,9 +1,9 @@
 "use client";
 import {
-  useMessageStore,
+  useMessageRuntime,
   useMessageUtilsStore,
 } from "../../context/react/MessageContext";
-import { useThreadStore } from "../../context/react/ThreadContext";
+import { useThreadRuntime } from "../../context/react/ThreadContext";
 import { useCombinedStore } from "../../utils/combined/useCombinedStore";
 
 export enum HideAndFloatStatus {
@@ -23,12 +23,12 @@ export const useActionBarFloatStatus = ({
   autohide,
   autohideFloat,
 }: UseActionBarFloatStatusProps) => {
-  const threadStore = useThreadStore();
-  const messageStore = useMessageStore();
+  const threadRuntime = useThreadRuntime();
+  const messageRuntime = useMessageRuntime();
   const messageUtilsStore = useMessageUtilsStore();
 
   return useCombinedStore(
-    [threadStore, messageStore, messageUtilsStore],
+    [threadRuntime, messageRuntime, messageUtilsStore],
     (t, m, mu) => {
       if (hideWhenRunning && t.isRunning) return HideAndFloatStatus.Hidden;
 
diff --git a/packages/react/src/primitives/composer/ComposerInput.tsx b/packages/react/src/primitives/composer/ComposerInput.tsx
index 0aaf7f914..98b382ca3 100644
--- a/packages/react/src/primitives/composer/ComposerInput.tsx
+++ b/packages/react/src/primitives/composer/ComposerInput.tsx
@@ -15,9 +15,13 @@ import TextareaAutosize, {
 } from "react-textarea-autosize";
 import {
   useComposer,
-  useComposerStore,
+  useComposerRuntime,
 } from "../../context/react/ComposerContext";
-import { useThread, useThreadStore } from "../../context/react/ThreadContext";
+import {
+  useThread,
+  useThreadRuntime,
+  useThreadViewportStore,
+} from "../../context/react/ThreadContext";
 import { useEscapeKeydown } from "@radix-ui/react-use-escape-keydown";
 import { useOnComposerFocus } from "../../utils/hooks/useOnComposerFocus";
 
@@ -52,8 +56,9 @@ export const ComposerPrimitiveInput = forwardRef<
     },
     forwardedRef,
   ) => {
-    const threadStore = useThreadStore();
-    const composerStore = useComposerStore();
+    const threadRuntime = useThreadRuntime();
+    const composerRuntime = useComposerRuntime();
+    const threadViewportStore = useThreadViewportStore({ optional: true });
 
     const value = useComposer((c) => {
       if (!c.isEditing) return "";
@@ -69,9 +74,8 @@ export const ComposerPrimitiveInput = forwardRef<
     useEscapeKeydown((e) => {
       if (!cancelOnEscape) return;
 
-      const composer = composerStore.getState();
-      if (composer.canCancel) {
-        composer.cancel();
+      if (composerRuntime.getState().canCancel) {
+        composerRuntime.cancel();
         e.preventDefault();
       }
     });
@@ -83,7 +87,7 @@ export const ComposerPrimitiveInput = forwardRef<
       if (e.nativeEvent.isComposing) return;
 
       if (e.key === "Enter" && e.shiftKey === false) {
-        const { isRunning } = threadStore.getState();
+        const { isRunning } = threadRuntime.getState();
 
         if (!isRunning) {
           e.preventDefault();
@@ -108,7 +112,7 @@ export const ComposerPrimitiveInput = forwardRef<
     useEffect(() => focus(), [focus]);
 
     useOnComposerFocus(() => {
-      if (composerStore.getState().type === "thread") {
+      if (composerRuntime.type === "thread") {
         focus();
       }
     });
@@ -121,9 +125,8 @@ export const ComposerPrimitiveInput = forwardRef<
         ref={ref}
         disabled={isDisabled}
         onChange={composeEventHandlers(onChange, (e) => {
-          const composerState = composerStore.getState();
-          if (!composerState.isEditing) return;
-          return composerState.setText(e.target.value);
+          if (!composerRuntime.getState().isEditing) return;
+          return composerRuntime.setText(e.target.value);
         })}
         onKeyDown={composeEventHandlers(onKeyDown, handleKeyPress)}
       />
diff --git a/packages/react/src/primitives/message/MessageContent.tsx b/packages/react/src/primitives/message/MessageContent.tsx
index 43095ce0e..a1d4a1615 100644
--- a/packages/react/src/primitives/message/MessageContent.tsx
+++ b/packages/react/src/primitives/message/MessageContent.tsx
@@ -1,11 +1,14 @@
 "use client";
 
 import { type ComponentType, type FC, memo, useMemo } from "react";
-import { useContentPart, useThreadRuntime, useToolUIs } from "../../context";
+import {
+  useContentPart,
+  useContentPartRuntime,
+  useToolUIs,
+} from "../../context";
 import {
   useMessage,
   useMessageRuntime,
-  useMessageStore,
 } from "../../context/react/MessageContext";
 import { ContentPartRuntimeProvider } from "../../context/providers/ContentPartRuntimeProvider";
 import { ContentPartPrimitiveText } from "../contentPart/ContentPartText";
@@ -85,8 +88,7 @@ const MessageContentPartComponent: FC<MessageContentPartComponentProps> = ({
     tools: { by_name = {}, Fallback = undefined } = {},
   } = {},
 }) => {
-  const messageStore = useMessageStore();
-  const threadRuntime = useThreadRuntime();
+  const contentPartRuntime = useContentPartRuntime();
 
   const part = useContentPart();
 
@@ -115,12 +117,7 @@ const MessageContentPartComponent: FC<MessageContentPartComponentProps> = ({
     case "tool-call": {
       const Tool = by_name[part.toolName] || Fallback;
       const addResult = (result: any) =>
-        threadRuntime.addToolResult({
-          messageId: messageStore.getState().id,
-          toolName: part.toolName,
-          toolCallId: part.toolCallId,
-          result,
-        });
+        contentPartRuntime.addToolResult(result);
       return (
         <ToolUIDisplay {...part} part={part} UI={Tool} addResult={addResult} />
       );