diff --git a/apps/web/src/components/ChatView.tsx b/apps/web/src/components/ChatView.tsx
index 37038e241154..62b9c655e634 100644
--- a/apps/web/src/components/ChatView.tsx
+++ b/apps/web/src/components/ChatView.tsx
@@ -6226,6 +6226,13 @@ export default function ChatView(props: ChatViewProps) {
         return;
       }
 
+      if (command === "reasoning.increase" || command === "reasoning.decrease") {
+        event.preventDefault();
+        event.stopPropagation();
+        composerRef.current?.adjustReasoningLevel(command === "reasoning.increase" ? 1 : -1);
+        return;
+      }
+
       if (command === "thread.stop") {
         // An unavailable command should not shadow contextual shortcuts such as Escape to close a dialog.
         if (!canInterruptRunningThread) return;
diff --git a/apps/web/src/components/chat/ChatComposer.tsx b/apps/web/src/components/chat/ChatComposer.tsx
index bff16c88bbcc..f64599a8fc60 100644
--- a/apps/web/src/components/chat/ChatComposer.tsx
+++ b/apps/web/src/components/chat/ChatComposer.tsx
@@ -177,6 +177,7 @@ import { ProviderModelPicker } from "./ProviderModelPicker";
 import { type ComposerCommandItem, ComposerCommandMenu } from "./ComposerCommandMenu";
 import { ComposerPendingApprovalActions } from "./ComposerPendingApprovalActions";
 import { CompactComposerControlsMenu } from "./CompactComposerControlsMenu";
+import { getReasoningLevelChange } from "./TraitsPicker";
 import { ComposerPrimaryActions } from "./ComposerPrimaryActions";
 import { ComposerPendingApprovalPanel } from "./ComposerPendingApprovalPanel";
 import { ComposerPendingUserInputPanel } from "./ComposerPendingUserInputPanel";
@@ -1185,6 +1186,7 @@ export interface ChatComposerHandle {
   openModelPicker: () => void;
   toggleModelPicker: () => void;
   isModelPickerOpen: () => boolean;
+  adjustReasoningLevel: (direction: 1 | -1) => void;
   compactContext: () => void;
   readSnapshot: () => {
     value: string;
@@ -4738,6 +4740,29 @@ export const ChatComposer = memo(function ChatComposer(props: ChatComposerProps)
           { ensureLeadingBoundary: true, citationCommentAnchor: sourceAnchor },
         ),
       openModelPicker,
+      adjustReasoningLevel: (direction) => {
+        if (noProviderAvailable || isComposerApprovalState || pendingUserInputs.length > 0) return;
+        const change = getReasoningLevelChange({
+          provider: selectedProvider,
+          models: selectedProviderModels,
+          model: selectedModel,
+          modelOptions: composerModelOptions?.[selectedInstanceId],
+          prompt: promptRef.current,
+          planModeEnabled: settings.planModeEnabled,
+          direction,
+        });
+        if (!change) return;
+        if ("modelOptions" in change) {
+          useComposerDraftStore
+            .getState()
+            .setProviderModelOptions(composerDraftTarget, selectedProvider, change.modelOptions, {
+              instanceId: selectedInstanceId,
+              model: selectedModel,
+              persistSticky: true,
+            });
+        }
+        if (change.prompt !== promptRef.current) setPromptFromTraits(change.prompt);
+      },
       toggleModelPicker: () => {
         if (isComposerModelPickerOpen) {
           setIsComposerModelPickerOpen(false);
@@ -4836,6 +4861,7 @@ export const ChatComposer = memo(function ChatComposer(props: ChatComposerProps)
       activeThread,
       addComposerAttachments,
       composerDraftTarget,
+      composerModelOptions,
       composerCursor,
       composerTerminalContexts,
       insertComposerDraftTerminalContext,
@@ -4858,6 +4884,7 @@ export const ChatComposer = memo(function ChatComposer(props: ChatComposerProps)
       isComposerModelPickerOpen,
       openModelPicker,
       readComposerSnapshot,
+      selectedInstanceId,
       selectedModel,
       selectedModelOptionsForDispatch,
       selectedModelSelection,
@@ -4866,6 +4893,8 @@ export const ChatComposer = memo(function ChatComposer(props: ChatComposerProps)
       selectedPromptEffort,
       selectedProvider,
       selectedProviderModels,
+      setPromptFromTraits,
+      settings.planModeEnabled,
       interactionMode,
       planModeUiEnabled,
       compactThreadContext,
diff --git a/apps/web/src/components/chat/TraitsPicker.test.ts b/apps/web/src/components/chat/TraitsPicker.test.ts
index dbe97cdd54e0..5f3b34a1b734 100644
--- a/apps/web/src/components/chat/TraitsPicker.test.ts
+++ b/apps/web/src/components/chat/TraitsPicker.test.ts
@@ -1,6 +1,14 @@
 import { describe, expect, it } from "vite-plus/test";
-import { ProviderDriverKind, type ProviderOptionDescriptor } from "@t3tools/contracts";
-import { buildTraitsTriggerDisplay, buildUnavailableModelOptionDescriptors } from "./TraitsPicker";
+import {
+  ProviderDriverKind,
+  type ProviderOptionDescriptor,
+  type ServerProviderModel,
+} from "@t3tools/contracts";
+import {
+  getReasoningLevelChange,
+  buildTraitsTriggerDisplay,
+  buildUnavailableModelOptionDescriptors,
+} from "./TraitsPicker";
 
 function selectDescriptor(
   id: string,
@@ -188,3 +196,106 @@ describe("buildUnavailableModelOptionDescriptors", () => {
     ]);
   });
 });
+
+describe("reasoning level shortcuts", () => {
+  const modelWith = (
+    descriptors: ReadonlyArray<ProviderOptionDescriptor>,
+  ): ReadonlyArray<ServerProviderModel> => [
+    {
+      slug: "test-model",
+      name: "Test",
+      isCustom: false,
+      capabilities: { optionDescriptors: descriptors },
+    },
+  ];
+  const options = [
+    { id: "low", label: "Low" },
+    { id: "high", label: "High", isDefault: true },
+    { id: "ultrathink", label: "Ultrathink" },
+  ];
+  const input = {
+    provider: CODEX,
+    model: "test-model",
+    models: modelWith([
+      { ...selectDescriptor("effort", options, "high"), promptInjectedValues: ["ultrathink"] },
+      fastModeDescriptor(false),
+    ]),
+    modelOptions: [{ id: "fastMode", value: true }],
+    prompt: "Solve this",
+    planModeEnabled: false,
+    direction: -1 as const,
+  };
+
+  it("steps from the default, skips unsupported levels, and preserves other traits", () => {
+    expect(
+      getReasoningLevelChange({
+        ...input,
+        models: modelWith([
+          { id: "effort", label: "Effort", type: "select", options },
+          fastModeDescriptor(false),
+        ]),
+      }),
+    ).toEqual({
+      prompt: "Solve this",
+      modelOptions: [
+        { id: "effort", value: "low" },
+        { id: "fastMode", value: true },
+      ],
+    });
+  });
+
+  it("stops at both ends", () => {
+    expect(
+      getReasoningLevelChange({ ...input, modelOptions: [{ id: "effort", value: "low" }] }),
+    ).toBeNull();
+    expect(
+      getReasoningLevelChange({ ...input, prompt: "Ultrathink:\nSolve this", direction: 1 }),
+    ).toBeNull();
+  });
+
+  it("enters and leaves prompt-controlled ultrathink", () => {
+    const increased = getReasoningLevelChange({ ...input, direction: 1 });
+    expect(increased).toEqual({ prompt: "Ultrathink:\nSolve this" });
+    expect(getReasoningLevelChange({ ...input, prompt: increased!.prompt })).toEqual({
+      prompt: "Solve this",
+      modelOptions: [
+        { id: "effort", value: "high" },
+        { id: "fastMode", value: true },
+      ],
+    });
+    expect(
+      getReasoningLevelChange({ ...input, prompt: "Please ultrathink about this" }),
+    ).toBeNull();
+  });
+
+  it("changes only the prompt when enabling ultrathink, and preserves slash commands", () => {
+    expect(getReasoningLevelChange({ ...input, prompt: "", direction: 1 })).toEqual({
+      prompt: "Ultrathink:\n",
+    });
+    expect(getReasoningLevelChange({ ...input, prompt: "/review", direction: 1 })).toEqual({
+      prompt: "/review",
+    });
+  });
+
+  it.each(["reasoningEffort", "effort", "variant"])("supports the %s descriptor", (id) => {
+    expect(
+      getReasoningLevelChange({
+        ...input,
+        models: modelWith([selectDescriptor(id, options, "high")]),
+      })?.modelOptions,
+    ).toEqual([{ id, value: "low" }]);
+  });
+
+  it.each(["agent", "contextWindow"])("does not step through %s options", (id) => {
+    expect(
+      getReasoningLevelChange({
+        ...input,
+        models: modelWith([selectDescriptor(id, options, "high")]),
+      }),
+    ).toBeNull();
+  });
+
+  it("does nothing when the model is unavailable", () => {
+    expect(getReasoningLevelChange({ ...input, models: [] })).toBeNull();
+  });
+});
diff --git a/apps/web/src/components/chat/TraitsPicker.tsx b/apps/web/src/components/chat/TraitsPicker.tsx
index 47ce59efde52..8db739869839 100644
--- a/apps/web/src/components/chat/TraitsPicker.tsx
+++ b/apps/web/src/components/chat/TraitsPicker.tsx
@@ -215,6 +215,68 @@ function getSelectedTraits(
   };
 }
 
+/** Resolve a picker or shortcut selection; prompt-only changes omit modelOptions to preserve preferences. */
+function getTraitSelectChange(
+  selected: ReturnType<typeof getSelectedTraits>,
+  descriptor: Extract<ProviderOptionDescriptor, { type: "select" }>,
+  prompt: string,
+  value: string,
+) {
+  if (!value) return null;
+  if (descriptor.promptInjectedValues?.includes(value)) {
+    return {
+      prompt:
+        prompt.trim().length === 0
+          ? ULTRATHINK_PROMPT_PREFIX
+          : applyClaudePromptEffortPrefix(prompt, "ultrathink"),
+    };
+  }
+  const isPrimary = descriptor.id === selected.primarySelectDescriptor?.id;
+  if (isPrimary && selected.ultrathinkInBodyText) return null;
+  return {
+    prompt:
+      isPrimary && selected.ultrathinkPromptControlled
+        ? prompt.replace(/^Ultrathink:\s*/i, "")
+        : prompt,
+    modelOptions: buildProviderOptionSelectionsFromDescriptors(
+      replaceDescriptorCurrentValue(selected.descriptors, descriptor.id, value),
+    ),
+  };
+}
+
+/** Step through the model's reasoning choices, stopping at either end. */
+export function getReasoningLevelChange(input: {
+  provider: ProviderDriverKind;
+  models: ReadonlyArray<ServerProviderModel>;
+  model: string;
+  prompt: string;
+  modelOptions: ProviderOptions | null | undefined;
+  planModeEnabled: boolean;
+  direction: 1 | -1;
+}) {
+  const selected = getSelectedTraits(
+    input.provider,
+    input.models,
+    input.model,
+    input.prompt,
+    input.modelOptions,
+    true,
+    input.planModeEnabled,
+  );
+  const descriptor = selected.selectDescriptors.find((entry) =>
+    ["reasoningEffort", "effort", "variant"].includes(entry.id),
+  );
+  if (!descriptor || selected.modelIsUnavailable || selected.ultrathinkInBodyText) return null;
+  const current = selected.ultrathinkPromptControlled
+    ? "ultrathink"
+    : getProviderOptionCurrentValue(descriptor);
+  const index = descriptor.options.findIndex((option) => option.id === current);
+  if (index < 0) return null;
+  const next = descriptor.options[index + input.direction];
+  if (!next) return null;
+  return getTraitSelectChange(selected, descriptor, input.prompt, next.id);
+}
+
 function getTraitsSectionVisibility(input: {
   provider: ProviderDriverKind;
   models: ReadonlyArray<ServerProviderModel>;
@@ -315,6 +377,15 @@ export const TraitsMenuContent = memo(function TraitsMenuContentImpl({
     },
     [instanceId, model, persistence, provider, setProviderModelOptions],
   );
+  const selected = getTraitsSectionVisibility({
+    provider,
+    models,
+    model,
+    prompt,
+    modelOptions,
+    allowPromptInjectedEffort,
+    planModeEnabled,
+  });
   const {
     descriptors,
     selectDescriptors,
@@ -324,38 +395,16 @@ export const TraitsMenuContent = memo(function TraitsMenuContentImpl({
     ultrathinkInBodyText,
     hasAnyControls,
     modelIsUnavailable,
-  } = getTraitsSectionVisibility({
-    provider,
-    models,
-    model,
-    prompt,
-    modelOptions,
-    allowPromptInjectedEffort,
-    planModeEnabled,
-  });
-  const updateDescriptors = (nextDescriptors: ReadonlyArray<ProviderOptionDescriptor>) => {
-    updateModelOptions(buildProviderOptionSelectionsFromDescriptors(nextDescriptors));
-  };
+  } = selected;
 
   const handleSelectChange = (
     descriptor: Extract<ProviderOptionDescriptor, { type: "select" }>,
     value: string,
   ) => {
-    if (!value) return;
-    if (descriptor.promptInjectedValues?.includes(value)) {
-      const nextPrompt =
-        prompt.trim().length === 0
-          ? ULTRATHINK_PROMPT_PREFIX
-          : applyClaudePromptEffortPrefix(prompt, "ultrathink");
-      onPromptChange(nextPrompt);
-      return;
-    }
-    if (ultrathinkInBodyText && descriptor.id === primarySelectDescriptor?.id) return;
-    if (ultrathinkPromptControlled && descriptor.id === primarySelectDescriptor?.id) {
-      const stripped = prompt.replace(/^Ultrathink:\s*/i, "");
-      onPromptChange(stripped);
-    }
-    updateDescriptors(replaceDescriptorCurrentValue(descriptors, descriptor.id, value));
+    const change = getTraitSelectChange(selected, descriptor, prompt, value);
+    if (!change) return;
+    if (change.prompt !== prompt) onPromptChange(change.prompt);
+    if ("modelOptions" in change) updateModelOptions(change.modelOptions);
   };
 
   if (!hasAnyControls) {
@@ -457,8 +506,10 @@ export const TraitsMenuContent = memo(function TraitsMenuContentImpl({
               <MenuRadioGroup
                 value={selectedValue}
                 onValueChange={(value) => {
-                  updateDescriptors(
-                    replaceDescriptorCurrentValue(descriptors, descriptor.id, value === "on"),
+                  updateModelOptions(
+                    buildProviderOptionSelectionsFromDescriptors(
+                      replaceDescriptorCurrentValue(descriptors, descriptor.id, value === "on"),
+                    ),
                   );
                 }}
               >
diff --git a/packages/contracts/src/keybindings.ts b/packages/contracts/src/keybindings.ts
index 2be8aa91f7aa..e96d5e2230a6 100644
--- a/packages/contracts/src/keybindings.ts
+++ b/packages/contracts/src/keybindings.ts
@@ -73,6 +73,8 @@ export const STATIC_KEYBINDING_COMMANDS = [
   "projectSearch.toggle",
   "themeEditor.toggle",
   "composer.stash",
+  "reasoning.increase",
+  "reasoning.decrease",
   "chat.new",
   "chat.newLocal",
   "editor.openFavorite",