diff --git a/.changeset/preserve-model-variants.md b/.changeset/preserve-model-variants.md
new file mode 100644
index 00000000000..10941827bb8
--- /dev/null
+++ b/.changeset/preserve-model-variants.md
@@ -0,0 +1,5 @@
+---
+"kilo-code": patch
+---
+
+Preserve the selected reasoning effort when switching to a model that supports the same or nearest available variant.
diff --git a/packages/kilo-vscode/tests/unit/mode-model.test.ts b/packages/kilo-vscode/tests/unit/mode-model.test.ts
index 9710bde9698..55f9a43f85b 100644
--- a/packages/kilo-vscode/tests/unit/mode-model.test.ts
+++ b/packages/kilo-vscode/tests/unit/mode-model.test.ts
@@ -13,8 +13,15 @@ describe("modelPatch", () => {
     })
   })
 
-  it("clears stale variant when next model does not support it", () => {
+  it("keeps the nearest supported effort when the exact variant is unavailable", () => {
     expect(modelPatch("kilo", "anthropic/claude-sonnet-4-6", ["low", "medium"], "high")).toEqual({
+      model: "kilo/anthropic/claude-sonnet-4-6",
+      variant: "medium",
+    })
+  })
+
+  it("clears an unknown variant when next model does not support it", () => {
+    expect(modelPatch("kilo", "anthropic/claude-sonnet-4-6", ["low", "medium"], "thinking")).toEqual({
       model: "kilo/anthropic/claude-sonnet-4-6",
       variant: null,
     })
diff --git a/packages/kilo-vscode/tests/unit/session-variant-store.test.ts b/packages/kilo-vscode/tests/unit/session-variant-store.test.ts
index a2b678009c3..5294c21f8ad 100644
--- a/packages/kilo-vscode/tests/unit/session-variant-store.test.ts
+++ b/packages/kilo-vscode/tests/unit/session-variant-store.test.ts
@@ -3,6 +3,7 @@ import {
   cycleVariant,
   getAgentVariant,
   getVariant,
+  preserveVariant,
   sessionVariantKeys,
   sessionVariants,
   transferVariants,
@@ -121,3 +122,24 @@ describe("cycleVariant", () => {
     expect(cycleVariant("low", [])).toBeUndefined()
   })
 })
+
+describe("preserveVariant", () => {
+  it("keeps an exact variant", () => {
+    expect(preserveVariant("high", ["low", "high"])).toBe("high")
+    expect(preserveVariant("thinking", ["instant", "thinking"])).toBe("thinking")
+    expect(preserveVariant("default", ["default", "thinking"])).toBe("default")
+  })
+
+  it("falls back to the nearest supported effort", () => {
+    expect(preserveVariant("max", ["high", "xhigh"])).toBe("xhigh")
+    expect(preserveVariant("high", ["low", "medium"])).toBe("medium")
+    expect(preserveVariant("max", ["none", "low"])).toBe("low")
+  })
+
+  it("does not cross binary or custom variant families", () => {
+    expect(preserveVariant("thinking", ["low", "high"])).toBeUndefined()
+    expect(preserveVariant("instant", ["low", "high"])).toBeUndefined()
+    expect(preserveVariant("turbo", ["low", "high"])).toBeUndefined()
+    expect(preserveVariant("high", ["instant", "thinking"])).toBeUndefined()
+  })
+})
diff --git a/packages/kilo-vscode/webview-ui/agent-manager/NewWorktreeDialog.tsx b/packages/kilo-vscode/webview-ui/agent-manager/NewWorktreeDialog.tsx
index a2d88dfbd5e..f265bc2d158 100644
--- a/packages/kilo-vscode/webview-ui/agent-manager/NewWorktreeDialog.tsx
+++ b/packages/kilo-vscode/webview-ui/agent-manager/NewWorktreeDialog.tsx
@@ -23,7 +23,7 @@ import { useServer } from "../src/context/server"
 import { useSession } from "../src/context/session"
 import { useProvider } from "../src/context/provider"
 import { useConfig } from "../src/context/config"
-import { cycleVariant } from "../src/context/session-variant-store"
+import { cycleVariant, preserveVariant } from "../src/context/session-variant-store"
 import { ModelSelectorBase } from "../src/components/shared/ModelSelector"
 import { ModeSwitcherBase } from "../src/components/shared/ModeSwitcher"
 import { SpeechToTextButton } from "../src/components/speech-to-text/SpeechToTextButton"
@@ -268,7 +268,7 @@ export const NewWorktreeDialog: Component<{
       return
     }
     const stored = variant()
-    if (!stored || !list.includes(stored)) setVariant(list[0])
+    if (!stored || !list.includes(stored)) setVariant(preserveVariant(stored, list) ?? list[0])
   })
 
   createEffect(() => {
@@ -871,7 +871,12 @@ export const NewWorktreeDialog: Component<{
                     <ModelSelectorBase
                       value={model()}
                       onSelect={(pid, mid) => {
-                        if (pid && mid) setModel({ providerID: pid, modelID: mid })
+                        if (!pid || !mid) return
+                        const current = effectiveVariant()
+                        const next = { providerID: pid, modelID: mid }
+                        const list = Object.keys(provider.findModel(next)?.variants ?? {})
+                        setModel(next)
+                        setVariant(preserveVariant(current, list))
                       }}
                       onPick={restorePrompt}
                       onCancel={restorePrompt}
diff --git a/packages/kilo-vscode/webview-ui/src/components/settings/ModelsTab.tsx b/packages/kilo-vscode/webview-ui/src/components/settings/ModelsTab.tsx
index 619cf17bd13..a87865044f7 100644
--- a/packages/kilo-vscode/webview-ui/src/components/settings/ModelsTab.tsx
+++ b/packages/kilo-vscode/webview-ui/src/components/settings/ModelsTab.tsx
@@ -16,6 +16,7 @@ import { DEFAULT_SPEECH_TO_TEXT_MODEL } from "../../../../src/speech-to-text/mod
 import { hasSpeechToTextAccess, selectedSpeechToTextModel } from "../speech-to-text/availability"
 import { speechToTextModelOptions } from "../speech-to-text/model-selector"
 import { AUTOCOMPLETE_SELECTOR_MODELS, getAutocompleteSelection } from "./autocomplete-model-selector"
+import { preserveVariant } from "../../context/session-variant-store"
 
 const ModelsTab: Component = () => {
   const { config, settings, updateConfig, updateSetting } = useConfig()
@@ -64,9 +65,12 @@ const ModelsTab: Component = () => {
       return
     }
     const value = `${providerID}/${modelID}`
+    const list = Object.keys(provider.findModel({ providerID, modelID })?.variants ?? {})
+    const next = preserveVariant(subagentVariant(), list)
     updateConfig({
       subagent_model: value,
       ...(config().subagent_model === value ? {} : { subagent_variant: null }),
+      ...(next ? { subagent_variant_overrides: { ...config().subagent_variant_overrides, [value]: next } } : {}),
     })
   }
 
@@ -87,7 +91,17 @@ const ModelsTab: Component = () => {
         updateConfig({ agent: { [agentName]: { model: null } } })
         return
       }
-      updateConfig({ agent: { [agentName]: { model: `${providerID}/${modelID}` } } })
+      const current = config().agent?.[agentName]?.variant ?? undefined
+      const list = Object.keys(provider.findModel({ providerID, modelID })?.variants ?? {})
+      const next = preserveVariant(current, list)
+      updateConfig({
+        agent: {
+          [agentName]: {
+            model: `${providerID}/${modelID}`,
+            ...(current && !list.includes(current) ? { variant: next ?? null } : {}),
+          },
+        },
+      })
     }
   }
 
diff --git a/packages/kilo-vscode/webview-ui/src/components/settings/agent-behaviour/WorkflowsTab.tsx b/packages/kilo-vscode/webview-ui/src/components/settings/agent-behaviour/WorkflowsTab.tsx
index afcbba8a83b..f0f9a91851d 100644
--- a/packages/kilo-vscode/webview-ui/src/components/settings/agent-behaviour/WorkflowsTab.tsx
+++ b/packages/kilo-vscode/webview-ui/src/components/settings/agent-behaviour/WorkflowsTab.tsx
@@ -9,6 +9,7 @@ import { ModelSelectorBase } from "../../shared/ModelSelector"
 import { ThinkingSelectorBase } from "../../shared/ThinkingSelector"
 import { parseModelString } from "../../../../../src/shared/provider-model"
 import type { CommandConfig } from "../../../types/messages"
+import { preserveVariant } from "../../../context/session-variant-store"
 
 const WorkflowsTab: Component = () => {
   const language = useLanguage()
@@ -48,9 +49,10 @@ const WorkflowsTab: Component = () => {
   const selectModel = (name: string, providerID: string, modelID: string) => {
     const list = Object.keys(provider.findModel({ providerID, modelID })?.variants ?? {})
     const current = variant(config().command?.[name] ?? {}, name)
+    const next = preserveVariant(current, list)
     update(name, {
       model: providerID && modelID ? `${providerID}/${modelID}` : null,
-      ...(current && !list.includes(current) ? { variant: null } : {}),
+      ...(current && !list.includes(current) ? { variant: next ?? null } : {}),
     })
   }
 
diff --git a/packages/kilo-vscode/webview-ui/src/components/settings/mode-model.ts b/packages/kilo-vscode/webview-ui/src/components/settings/mode-model.ts
index 7abbac3f672..e39eb19e612 100644
--- a/packages/kilo-vscode/webview-ui/src/components/settings/mode-model.ts
+++ b/packages/kilo-vscode/webview-ui/src/components/settings/mode-model.ts
@@ -1,4 +1,5 @@
 import type { AgentConfig } from "../../types/messages"
+import { preserveVariant } from "../../context/session-variant-store"
 
 export function modelPatch(
   providerID: string,
@@ -12,6 +13,6 @@ export function modelPatch(
 
   return {
     model: `${providerID}/${modelID}`,
-    ...(current && !variants.includes(current) ? { variant: null } : {}),
+    ...(current && !variants.includes(current) ? { variant: preserveVariant(current, variants) ?? null } : {}),
   }
 }
diff --git a/packages/kilo-vscode/webview-ui/src/context/session-variant-store.ts b/packages/kilo-vscode/webview-ui/src/context/session-variant-store.ts
index bbbb5ca5a8a..0eb363b0d29 100644
--- a/packages/kilo-vscode/webview-ui/src/context/session-variant-store.ts
+++ b/packages/kilo-vscode/webview-ui/src/context/session-variant-store.ts
@@ -1,5 +1,26 @@
 import type { ModelSelection } from "../types/messages"
 
+const effort = ["none", "minimal", "low", "medium", "high", "xhigh", "max"]
+
+/** Keep the selected effort when possible, falling back to the nearest known effort. */
+export function preserveVariant(current: string | undefined, variants: string[]) {
+  if (!current || variants.length === 0) return undefined
+  if (variants.includes(current)) return current
+
+  const rank = effort.indexOf(current)
+  if (rank === -1) return undefined
+
+  return variants
+    .map((value, index) => ({
+      value,
+      index,
+      rank: effort.indexOf(value),
+      distance: Math.abs(effort.indexOf(value) - rank),
+    }))
+    .filter((item) => effort.includes(item.value))
+    .sort((a, b) => a.distance - b.distance || b.rank - a.rank || a.index - b.index)[0]?.value
+}
+
 export function legacyVariantKey(sel: ModelSelection) {
   return `${sel.providerID}/${sel.modelID}`
 }
@@ -21,7 +42,7 @@ export function getVariant(
   const key = variantKey(sel, agent, session)
   const fallback = session ? store[variantKey(sel, agent)] : undefined
   const stored = store[key] ?? fallback ?? store[legacyVariantKey(sel)]
-  return stored && variants.includes(stored) ? stored : variants[0]
+  return preserveVariant(stored, variants) ?? variants[0]
 }
 
 export function getAgentVariant(
diff --git a/packages/kilo-vscode/webview-ui/src/context/session.tsx b/packages/kilo-vscode/webview-ui/src/context/session.tsx
index dcfd8e57e24..839b0dc3f50 100644
--- a/packages/kilo-vscode/webview-ui/src/context/session.tsx
+++ b/packages/kilo-vscode/webview-ui/src/context/session.tsx
@@ -74,7 +74,14 @@ import { errorIDs } from "./session-errors"
 import { PartStash } from "./part-stash"
 import { mergeParts, sameParts } from "./session-parts"
 import { state as todoState } from "./todo-revert"
-import { getAgentVariant, getVariant, sessionVariantKeys, transferVariants, variantKey } from "./session-variant-store"
+import {
+  getAgentVariant,
+  getVariant,
+  preserveVariant,
+  sessionVariantKeys,
+  transferVariants,
+  variantKey,
+} from "./session-variant-store"
 import { KILO_AUTO, KILO_PROVIDER_ID, parseModelString } from "../../../src/shared/provider-model"
 import { reviewMetadata, type ReviewMessageData } from "../../../src/shared/review-comments"
 import { visibleMessages as filterVisibleMessages } from "./session-queue"
@@ -663,9 +670,22 @@ export const SessionProvider: ParentComponent = (props) => {
     })
   }
 
+  function carryVariant(selection: ModelSelection, current: string | undefined, agent: string, sessionID?: string) {
+    const value = preserveVariant(current, Object.keys(provider.findModel(selection)?.variants ?? {}))
+    if (!value) return
+    const key = variantKey(selection, agent, sessionID)
+    setStore("variantSelections", key, value)
+    if (!sessionID) vscode.postMessage({ type: "persistVariant", key, value })
+  }
+
   function selectModel(providerID: string, modelID: string, sessionID?: string) {
     const sid = sessionID ?? currentSessionID()
-    applyModel(agentForScope(sid), { providerID, modelID }, sid)
+    const agent = agentForScope(sid)
+    const current = selected(sid)
+    const value = current ? currentVariant(sid) : undefined
+    const selection = { providerID, modelID }
+    applyModel(agent, selection, sid)
+    carryVariant(selection, value, agent, sid)
     if (sid) {
       hideErrors(sid)
     }
@@ -3033,8 +3053,12 @@ export const SessionProvider: ParentComponent = (props) => {
       // agent may not yet be assigned (sendInitialMessage calls setSessionModel
       // before setSessionAgent), so the write would land on defaultAgent() and
       // corrupt the default mode's model for later sessions.
+      const agent = store.agentSelections[sessionID] ?? defaultAgent()
+      const current = selected(sessionID)
+      const value = current ? currentVariant(sessionID) : undefined
       const model = { providerID, modelID }
       setStore("sessionOverrides", sessionID, model)
+      carryVariant(model, value, agent, sessionID)
     },
     setSessionAgent: (sessionID: string, name: string) => {
       setStore("agentSelections", sessionID, name)
diff --git a/packages/opencode/src/cli/cmd/run/footer.ts b/packages/opencode/src/cli/cmd/run/footer.ts
index 64d06dfcfc6..3abd5c312a3 100644
--- a/packages/opencode/src/cli/cmd/run/footer.ts
+++ b/packages/opencode/src/cli/cmd/run/footer.ts
@@ -834,11 +834,7 @@ export class RunFooter implements FooterApi {
       return
     }
 
-    const previous = this.currentModel()
     this.setCurrentModel(model)
-    if (!previous || previous.providerID !== model.providerID || previous.modelID !== model.modelID) {
-      this.setCurrentVariant(undefined)
-    }
     void Promise.resolve()
       .then(() => this.options.onModelSelect?.(model))
       .then((result) => {
diff --git a/packages/opencode/src/cli/cmd/run/runtime.ts b/packages/opencode/src/cli/cmd/run/runtime.ts
index f459fdea8b7..2cc8ae67341 100644
--- a/packages/opencode/src/cli/cmd/run/runtime.ts
+++ b/packages/opencode/src/cli/cmd/run/runtime.ts
@@ -21,6 +21,8 @@ import { resolveModelInfo, resolveRunTuiConfig, resolveSessionInfo } from "./run
 import { createRuntimeLifecycle } from "./runtime.lifecycle"
 import { trace } from "./trace"
 import { cycleVariant, formatModelLabel, resolveSavedVariant, resolveVariant, saveVariant } from "./variant.shared"
+// kilocode_change - preserve compatible variants when switching models
+import { resolvePreservedVariant } from "@/kilocode/cli/cmd/run/variant" // kilocode_change
 import type { LocalReplayAnchor, LocalReplayRow, RunInput, RunPrompt, RunProvider, StreamCommit } from "./types"
 
 /** @internal Exported for testing */
@@ -294,8 +296,9 @@ async function runInteractiveRuntime(input: RunRuntimeInput, deps: RunRuntimeDep
         return
       }
 
+      // kilocode_change start - preserve the active effort across model switches
+      const previous = state.activeVariant
       state.model = model
-      state.activeVariant = undefined
       state.variants = variantsFor(state.providers, model)
       const switching = resolveSavedVariant(model).then((saved) => {
         const current = state.model
@@ -303,8 +306,12 @@ async function runInteractiveRuntime(input: RunRuntimeInput, deps: RunRuntimeDep
           return
         }
 
-        state.activeVariant = resolveVariant(ctx.variant, undefined, saved, state.variants)
+        // kilocode_change - prefer the active effort over a model-specific saved preference
+        state.activeVariant =
+          resolvePreservedVariant(ctx.variant, previous, state.variants) ??
+          resolveVariant(ctx.variant, undefined, saved, state.variants)
       })
+      // kilocode_change end
       state.switching = switching
       await switching
       if (state.switching === switching) {
@@ -440,10 +447,14 @@ async function runInteractiveRuntime(input: RunRuntimeInput, deps: RunRuntimeDep
     state.variants = variantsFor(state.providers, state.model)
     state.limits = info.limits
 
-    const next = resolveVariant(ctx.variant, session.variant, savedVariant, state.variants)
+    // kilocode_change start - preserve the active effort when the model catalog arrives asynchronously
+    const next =
+      resolvePreservedVariant(ctx.variant, state.activeVariant, state.variants) ??
+      resolveVariant(ctx.variant, session.variant, savedVariant, state.variants)
     if (next !== state.activeVariant) {
       state.activeVariant = next
     }
+    // kilocode_change end
 
     if (footer.isClosed) {
       return
diff --git a/packages/opencode/src/kilocode/cli/cmd/run/variant.ts b/packages/opencode/src/kilocode/cli/cmd/run/variant.ts
new file mode 100644
index 00000000000..ed2d85c1a8b
--- /dev/null
+++ b/packages/opencode/src/kilocode/cli/cmd/run/variant.ts
@@ -0,0 +1,29 @@
+const effort = ["none", "minimal", "low", "medium", "high", "xhigh", "max"]
+
+/** Keep an explicit CLI variant verbatim; only infer a fallback for automatic selections. */
+export function resolvePreservedVariant(
+  input: string | undefined,
+  current: string | undefined,
+  variants: string[],
+): string | undefined {
+  return input ?? preserveVariant(current, variants)
+}
+
+/** Keep the selected effort when possible, falling back to the nearest known effort. */
+export function preserveVariant(current: string | undefined, variants: string[]): string | undefined {
+  if (!current || variants.length === 0) return undefined
+  if (variants.includes(current)) return current
+
+  const rank = effort.indexOf(current)
+  if (rank === -1) return undefined
+
+  return variants
+    .map((value, index) => ({
+      value,
+      index,
+      rank: effort.indexOf(value),
+      distance: Math.abs(effort.indexOf(value) - rank),
+    }))
+    .filter((item) => effort.includes(item.value))
+    .sort((a, b) => a.distance - b.distance || b.rank - a.rank || a.index - b.index)[0]?.value
+}
diff --git a/packages/opencode/test/kilocode/cli/run/variant.test.ts b/packages/opencode/test/kilocode/cli/run/variant.test.ts
new file mode 100644
index 00000000000..608e4452db2
--- /dev/null
+++ b/packages/opencode/test/kilocode/cli/run/variant.test.ts
@@ -0,0 +1,28 @@
+import { describe, expect, test } from "bun:test"
+import { preserveVariant, resolvePreservedVariant } from "@/kilocode/cli/cmd/run/variant"
+
+describe("Kilo CLI variant preservation", () => {
+  test("keeps exact variants across supported families", () => {
+    expect(preserveVariant("high", ["low", "high"])).toBe("high")
+    expect(preserveVariant("thinking", ["instant", "thinking"])).toBe("thinking")
+    expect(preserveVariant("default", ["default", "thinking"])).toBe("default")
+  })
+
+  test("keeps an explicit CLI variant verbatim", () => {
+    expect(resolvePreservedVariant("max", "high", ["low", "medium", "high"])).toBe("max")
+    expect(resolvePreservedVariant("thinking", "high", ["low", "medium", "high"])).toBe("thinking")
+  })
+
+  test("falls back to the nearest supported reasoning effort", () => {
+    expect(preserveVariant("max", ["high", "xhigh"])).toBe("xhigh")
+    expect(preserveVariant("high", ["low", "medium"])).toBe("medium")
+    expect(preserveVariant("max", ["none", "low"])).toBe("low")
+  })
+
+  test("does not cross binary or custom variant families", () => {
+    expect(preserveVariant("thinking", ["low", "high"])).toBeUndefined()
+    expect(preserveVariant("instant", ["low", "high"])).toBeUndefined()
+    expect(preserveVariant("turbo", ["low", "high"])).toBeUndefined()
+    expect(preserveVariant("high", ["instant", "thinking"])).toBeUndefined()
+  })
+})