feat: add agent default variant handling in TUI and desktop

packages/app/src/context/local.tsx

@@ -6,7 +6,7 @@ import { createStore } from "solid-js/store"
 import { useModels } from "@/context/models"
 import { useProviders } from "@/hooks/use-providers"
 import { Persist, persisted } from "@/utils/persist"
-import { cycleModelVariant, getConfiguredAgentVariant, resolveModelVariant } from "./model-variant"
+import { cycleModelVariant, getConfiguredAgentVariant, resolveModelVariant } from "@opencode-ai/core/util/model-variant"
 import { useSDK } from "./sdk"
 import { useSync } from "./sync"
 

packages/app/src/context/model-variant.ts → packages/core/src/util/model-variant.ts

@@ -12,6 +12,9 @@ type Model = AgentModel & {
   variants?: Record<string, unknown>
 }
 
+// selected: string          = user-chosen variant name
+// selected: null            = user explicitly chose "default" (clears any agent-configured variant)
+// selected: undefined       = no user choice yet (fall back to agent-configured variant)
 type VariantInput = {
   variants: string[]
   selected: string | null | undefined
@@ -43,6 +46,7 @@ export function cycleModelVariant(input: VariantInput) {
     if (index === input.variants.length - 1) return undefined
     return input.variants[index + 1]
   }
+  // No explicit selection: start cycling from the agent-configured variant.
   if (input.configured && input.variants.includes(input.configured)) {
     const index = input.variants.indexOf(input.configured)
     if (index === input.variants.length - 1) return input.variants[0]

packages/app/src/context/model-variant.test.ts → packages/core/test/util/model-variant.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, test } from "bun:test"
-import { cycleModelVariant, getConfiguredAgentVariant, resolveModelVariant } from "./model-variant"
+import { cycleModelVariant, getConfiguredAgentVariant, resolveModelVariant } from "../../src/util/model-variant"
 
 describe("model variant", () => {
   test("resolves configured agent variant when model matches", () => {
@@ -83,4 +83,17 @@ describe("model variant", () => {
 
     expect(value).toBe("low")
   })
+
+  test("cycles through all variants from explicit selection", () => {
+    const variants = ["low", "high", "xhigh"]
+    const first = cycleModelVariant({ variants, selected: undefined, configured: undefined })
+    const second = cycleModelVariant({ variants, selected: first, configured: undefined })
+    const third = cycleModelVariant({ variants, selected: second, configured: undefined })
+    const fourth = cycleModelVariant({ variants, selected: third, configured: undefined })
+
+    expect(first).toBe("low")
+    expect(second).toBe("high")
+    expect(third).toBe("xhigh")
+    expect(fourth).toBeUndefined()
+  })
 })

packages/opencode/src/cli/cmd/tui/component/dialog-model.tsx

@@ -135,8 +135,13 @@ export function DialogModel(props: { providerID?: string }) {
   function onSelect(providerID: string, modelID: string) {
     local.model.set({ providerID, modelID }, { recent: true })
     const list = local.model.variant.list()
-    const cur = local.model.variant.selected()
-    if (cur === "default" || (cur && list.includes(cur))) {
+    const selected = local.model.variant.selected()
+    const current = local.model.variant.current()
+    if (
+      selected === null ||
+      (selected && list.includes(selected)) ||
+      (!selected && current && list.includes(current))
+    ) {
       dialog.clear()
       return
     }

packages/opencode/src/cli/cmd/tui/component/dialog-variant.tsx

@@ -32,7 +32,7 @@ export function DialogVariant() {
     <DialogSelect<string>
       options={options()}
       title={"Select variant"}
-      current={local.model.variant.selected()}
+      current={local.model.variant.current() ?? "default"}
       flat={true}
     />
   )

packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx

@@ -287,7 +287,13 @@ export function Prompt(props: PromptProps) {
         if (!args.agent) local.agent.set(msg.agent)
         if (msg.model) {
           local.model.set(msg.model)
-          local.model.variant.set(msg.model.variant)
+          const configured = local.model.variant.configured()
+          if (!msg.model.variant || msg.model.variant === configured) {
+            local.model.variant.clear()
+          }
+          if (msg.model.variant && msg.model.variant !== configured) {
+            local.model.variant.set(msg.model.variant)
+          }
         }
       }
     }

packages/opencode/src/cli/cmd/tui/context/local.tsx

@@ -12,6 +12,7 @@ import { useArgs } from "./args"
 import { useSDK } from "./sdk"
 import { RGBA } from "@opentui/core"
 import { Filesystem } from "@/util/filesystem"
+import { cycleModelVariant, getConfiguredAgentVariant, resolveModelVariant } from "@opencode-ai/core/util/model-variant"
 
 export function parseModel(model: string) {
   const [providerID, ...rest] = model.split("/")
@@ -118,7 +119,7 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
           providerID: string
           modelID: string
         }[]
-        variant: Record<string, string | undefined>
+        variant: Record<string, string | null | undefined>
       }>({
         ready: false,
         model: {},
@@ -149,7 +150,16 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
         .then((x: any) => {
           if (Array.isArray(x.recent)) setModelStore("recent", x.recent)
           if (Array.isArray(x.favorite)) setModelStore("favorite", x.favorite)
-          if (typeof x.variant === "object" && x.variant !== null) setModelStore("variant", x.variant)
+          if (typeof x.variant === "object" && x.variant !== null) {
+            const variant = Object.fromEntries(
+              Object.entries(x.variant).map(([key, value]) => [
+                key,
+                value === "default" ? null : typeof value === "string" || value === null ? value : undefined,
+              ]),
+            ) as Record<string, string | null | undefined>
+            setModelStore("variant", variant)
+            if (Object.values(x.variant).includes("default")) state.pending = true
+          }
         })
         .catch(() => {})
         .finally(() => {
@@ -334,17 +344,29 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
           })
         },
         variant: {
+          configured() {
+            const a = agent.current()
+            const m = currentModel()
+            if (!m || !a) return undefined
+            const provider = sync.data.provider.find((x) => x.id === m.providerID)
+            const info = provider?.models[m.modelID]
+            return getConfiguredAgentVariant({
+              agent: { model: a.model, variant: a.variant },
+              model: { providerID: m.providerID, modelID: m.modelID, variants: info?.variants },
+            })
+          },
           selected() {
             const m = currentModel()
             if (!m) return undefined
             const key = `${m.providerID}/${m.modelID}`
             return modelStore.variant[key]
           },
           current() {
-            const v = this.selected()
-            if (!v) return undefined
-            if (!this.list().includes(v)) return undefined
-            return v
+            return resolveModelVariant({
+              variants: this.list(),
+              selected: this.selected(),
+              configured: this.configured(),
+            })
           },
           list() {
             const m = currentModel()
@@ -358,23 +380,26 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
             const m = currentModel()
             if (!m) return
             const key = `${m.providerID}/${m.modelID}`
-            setModelStore("variant", key, value ?? "default")
+            setModelStore("variant", key, value ?? null)
+            save()
+          },
+          clear() {
+            const m = currentModel()
+            if (!m) return
+            const key = `${m.providerID}/${m.modelID}`
+            setModelStore("variant", key, undefined)
             save()
           },
           cycle() {
             const variants = this.list()
             if (variants.length === 0) return
-            const current = this.current()
-            if (!current) {
-              this.set(variants[0])
-              return
-            }
-            const index = variants.indexOf(current)
-            if (index === -1 || index === variants.length - 1) {
-              this.set(undefined)
-              return
-            }
-            this.set(variants[index + 1])
+            this.set(
+              cycleModelVariant({
+                variants,
+                selected: this.selected(),
+                configured: this.configured(),
+              }),
+            )
           },
         },
       }

packages/opencode/test/agent/agent.test.ts

@@ -740,3 +740,21 @@ test("defaultAgent throws when all primary agents are disabled", async () => {
     },
   })
 })
+
+test("agent variant can be set from config", async () => {
+  await using tmp = await tmpdir({
+    config: {
+      agent: {
+        build: { variant: "high" },
+      },
+    },
+  })
+  const build = await load(tmp.path, (svc) => svc.get("build"))
+  expect(build?.variant).toBe("high")
+})
+
+test("agent variant defaults to undefined when not set", async () => {
+  await using tmp = await tmpdir()
+  const build = await load(tmp.path, (svc) => svc.get("build"))
+  expect(build?.variant).toBeUndefined()
+})