From e73ec6d2d7e3a93f648195d04e3b9786f04913e5 Mon Sep 17 00:00:00 2001
From: Rhys Sullivan <39114868+RhysSullivan@users.noreply.github.com>
Date: Mon, 16 Mar 2026 11:46:41 -0700
Subject: [PATCH] feat(model): add provider fast mode toggle

---
 packages/app/src/components/prompt-input.tsx  | 23 +++++++
 .../app/src/components/prompt-input/submit.ts |  7 ++
 packages/app/src/context/local.tsx            | 42 +++++++++++-
 packages/app/src/context/model-fast.ts        | 28 ++++++++
 packages/app/src/i18n/en.ts                   |  4 ++
 .../session/session-model-helpers.test.ts     | 20 +++++-
 .../pages/session/use-session-commands.tsx    |  8 +++
 packages/app/src/testing/model-selection.ts   |  5 +-
 .../cli/cmd/tui/component/prompt/index.tsx    | 27 +++++++-
 .../src/cli/cmd/tui/context/local.tsx         | 35 ++++++++++
 packages/opencode/src/provider/fast.ts        | 45 +++++++++++++
 packages/opencode/src/provider/transform.ts   |  5 ++
 packages/opencode/src/session/compaction.ts   |  1 +
 packages/opencode/src/session/llm.ts          | 12 ++--
 packages/opencode/src/session/message-v2.ts   |  2 +
 packages/opencode/src/session/prompt.ts       |  7 ++
 .../opencode/test/provider/transform.test.ts  | 64 +++++++++++++++++++
 packages/sdk/js/src/v2/gen/sdk.gen.ts         |  6 ++
 packages/sdk/js/src/v2/gen/types.gen.ts       |  5 ++
 19 files changed, 337 insertions(+), 9 deletions(-)
 create mode 100644 packages/app/src/context/model-fast.ts
 create mode 100644 packages/opencode/src/provider/fast.ts

diff --git a/packages/app/src/components/prompt-input.tsx b/packages/app/src/components/prompt-input.tsx
index b2553e4c02..3d8455f926 100644
--- a/packages/app/src/components/prompt-input.tsx
+++ b/packages/app/src/components/prompt-input.tsx
@@ -1023,6 +1023,10 @@ export const PromptInput: Component<PromptInputProps> = (props) => {
   })
 
   const variants = createMemo(() => ["default", ...local.model.variant.list()])
+  const fast = createMemo(() => local.model.fast.available())
+  const fastLabel = createMemo(() =>
+    language.t(local.model.fast.current() ? "command.model.fast.disable" : "command.model.fast.enable"),
+  )
   const accepting = createMemo(() => {
     const id = params.id
     if (!id) return permission.isAutoAcceptingDirectory(sdk.directory)
@@ -1534,6 +1538,25 @@ export const PromptInput: Component<PromptInputProps> = (props) => {
                     />
                   </TooltipKeybind>
                 </div>
+                <Show when={fast()}>
+                  <Tooltip placement="top" gutter={8} value={fastLabel()}>
+                    <Button
+                      data-action="prompt-fast"
+                      variant="ghost"
+                      onClick={() => local.model.fast.toggle()}
+                      class="h-7 px-2 shrink-0 text-13-medium"
+                      classList={{
+                        "text-text-base": !local.model.fast.current(),
+                        "text-icon-warning-base bg-surface-warning-base": local.model.fast.current(),
+                      }}
+                      style={control()}
+                      aria-label={fastLabel()}
+                      aria-pressed={local.model.fast.current()}
+                    >
+                      {language.t("command.model.fast.label")}
+                    </Button>
+                  </Tooltip>
+                </Show>
                 <TooltipKeybind
                   placement="top"
                   gutter={8}
diff --git a/packages/app/src/components/prompt-input/submit.ts b/packages/app/src/components/prompt-input/submit.ts
index ba299fe365..38ae8ca57a 100644
--- a/packages/app/src/components/prompt-input/submit.ts
+++ b/packages/app/src/components/prompt-input/submit.ts
@@ -34,6 +34,7 @@ export type FollowupDraft = {
   agent: string
   model: { providerID: string; modelID: string }
   variant?: string
+  fast?: boolean
 }
 
 type FollowupSendInput = {
@@ -88,6 +89,7 @@ export async function sendFollowupDraft(input: FollowupSendInput) {
         agent: input.draft.agent,
         model: `${input.draft.model.providerID}/${input.draft.model.modelID}`,
         variant: input.draft.variant,
+        fast: input.draft.fast,
         parts: images.map((attachment) => ({
           id: Identifier.ascending("part"),
           type: "file" as const,
@@ -122,6 +124,7 @@ export async function sendFollowupDraft(input: FollowupSendInput) {
     agent: input.draft.agent,
     model: input.draft.model,
     variant: input.draft.variant,
+    fast: input.draft.fast,
   }
 
   const add = () =>
@@ -156,6 +159,7 @@ export async function sendFollowupDraft(input: FollowupSendInput) {
       messageID,
       parts: requestParts,
       variant: input.draft.variant,
+      fast: input.draft.fast,
     })
     return true
   } catch (err) {
@@ -297,6 +301,7 @@ export function createPromptSubmit(input: PromptSubmitInput) {
     const currentModel = local.model.current()
     const currentAgent = local.agent.current()
     const variant = local.model.variant.current()
+    const fast = local.model.fast.current()
     if (!currentModel || !currentAgent) {
       showToast({
         title: language.t("prompt.toast.modelAgentRequired.title"),
@@ -398,6 +403,7 @@ export function createPromptSubmit(input: PromptSubmitInput) {
       agent,
       model,
       variant,
+      fast,
     }
 
     const clearInput = () => {
@@ -461,6 +467,7 @@ export function createPromptSubmit(input: PromptSubmitInput) {
             agent,
             model: `${model.providerID}/${model.modelID}`,
             variant,
+            fast,
             parts: images.map((attachment) => ({
               id: Identifier.ascending("part"),
               type: "file" as const,
diff --git a/packages/app/src/context/local.tsx b/packages/app/src/context/local.tsx
index bed7ecd15c..061ba643ee 100644
--- a/packages/app/src/context/local.tsx
+++ b/packages/app/src/context/local.tsx
@@ -8,6 +8,7 @@ import { useProviders } from "@/hooks/use-providers"
 import { modelEnabled, modelProbe } from "@/testing/model-selection"
 import { Persist, persisted } from "@/utils/persist"
 import { cycleModelVariant, getConfiguredAgentVariant, resolveModelVariant } from "./model-variant"
+import * as Fast from "./model-fast"
 import { useSDK } from "./sdk"
 import { useSync } from "./sync"
 
@@ -17,6 +18,7 @@ type State = {
   agent?: string
   model?: ModelKey
   variant?: string | null
+  fast?: boolean
 }
 
 type Saved = {
@@ -79,10 +81,11 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
       current?: string
       draft?: State
       last?: {
-        type: "agent" | "model" | "variant"
+        type: "agent" | "model" | "variant" | "fast"
         agent?: string
         model?: ModelKey | null
         variant?: string | null
+        fast?: boolean
       }
     }>({
       current: list()[0]?.name,
@@ -191,11 +194,13 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
             agent: item.name,
             model: item.model,
             variant: item.variant ?? null,
+            fast: scope()?.fast,
           })
           const next = {
             agent: item.name,
             model: item.model,
             variant: item.variant,
+            fast: scope()?.fast,
           } satisfies State
           const session = id()
           if (session) {
@@ -249,6 +254,7 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
         agent: agent.current()?.name,
         model: model ? { providerID: model.provider.id, modelID: model.id } : undefined,
         variant: selected(),
+        fast: !!scope()?.fast && Fast.enabled(model),
       } satisfies State
     }
 
@@ -296,6 +302,7 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
             agent: agent.current()?.name,
             model: item ?? null,
             variant: selected(),
+            fast: model.fast.current(),
           })
           write({ model: item })
           if (!item) return
@@ -333,6 +340,7 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
               agent: agent.current()?.name,
               model: model ? { providerID: model.provider.id, modelID: model.id } : null,
               variant: value ?? null,
+              fast: !!scope()?.fast && Fast.enabled(model),
             })
             write({ variant: value ?? null })
           })
@@ -349,6 +357,34 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
           )
         },
       },
+      fast: {
+        selected() {
+          return scope()?.fast === true
+        },
+        current() {
+          return this.selected() && this.available()
+        },
+        available() {
+          return Fast.enabled(current())
+        },
+        set(value: boolean) {
+          if (value && !this.available()) return
+          const model = current()
+          batch(() => {
+            setStore("last", {
+              type: "fast",
+              agent: agent.current()?.name,
+              model: model ? { providerID: model.provider.id, modelID: model.id } : null,
+              variant: selected(),
+              fast: value,
+            })
+            write({ fast: value || undefined })
+          })
+        },
+        toggle() {
+          this.set(!this.current())
+        },
+      },
     }
 
     const result = {
@@ -372,7 +408,7 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
           handoff.set(handoffKey(dir, session), next)
           setStore("draft", undefined)
         },
-        restore(msg: { sessionID: string; agent: string; model: ModelKey; variant?: string }) {
+        restore(msg: { sessionID: string; agent: string; model: ModelKey; variant?: string; fast?: boolean }) {
           const session = id()
           if (!session) return
           if (msg.sessionID !== session) return
@@ -383,6 +419,7 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
             agent: msg.agent,
             model: msg.model,
             variant: msg.variant ?? null,
+            fast: msg.fast === true,
           })
         },
       },
@@ -405,6 +442,7 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
               }
             : undefined,
           variant: result.model.variant.current() ?? null,
+          fast: result.model.fast.current(),
           selected: result.model.variant.selected(),
           configured: result.model.variant.configured(),
           pick: scope(),
diff --git a/packages/app/src/context/model-fast.ts b/packages/app/src/context/model-fast.ts
new file mode 100644
index 0000000000..f140807569
--- /dev/null
+++ b/packages/app/src/context/model-fast.ts
@@ -0,0 +1,28 @@
+type Model = {
+  id: string
+  provider: {
+    id: string
+  }
+}
+
+function lower(model: Model) {
+  return model.id.toLowerCase()
+}
+
+export function kind(model: Model | undefined) {
+  if (!model) return
+  const id = lower(model)
+  if (
+    model.provider.id === "anthropic" &&
+    (id.includes("claude-opus-4-6") || id.includes("claude-opus-4.6") || id.includes("opus-4-6"))
+  ) {
+    return "claude"
+  }
+  if (model.provider.id === "openai" && id.includes("gpt-5.4")) {
+    return "codex"
+  }
+}
+
+export function enabled(model: Model | undefined) {
+  return !!kind(model)
+}
diff --git a/packages/app/src/i18n/en.ts b/packages/app/src/i18n/en.ts
index ad12e1e0de..7bdfe6bbf2 100644
--- a/packages/app/src/i18n/en.ts
+++ b/packages/app/src/i18n/en.ts
@@ -67,6 +67,10 @@ export const dict = {
   "command.agent.cycle.description": "Switch to the next agent",
   "command.agent.cycle.reverse": "Cycle agent backwards",
   "command.agent.cycle.reverse.description": "Switch to the previous agent",
+  "command.model.fast.label": "Fast",
+  "command.model.fast.enable": "Enable fast mode",
+  "command.model.fast.disable": "Disable fast mode",
+  "command.model.fast.description": "Toggle provider fast mode for supported Claude and Codex models",
   "command.model.variant.cycle": "Cycle thinking effort",
   "command.model.variant.cycle.description": "Switch to the next effort level",
   "command.prompt.mode.shell": "Shell",
diff --git a/packages/app/src/pages/session/session-model-helpers.test.ts b/packages/app/src/pages/session/session-model-helpers.test.ts
index 319db805d2..36494d19b9 100644
--- a/packages/app/src/pages/session/session-model-helpers.test.ts
+++ b/packages/app/src/pages/session/session-model-helpers.test.ts
@@ -2,7 +2,7 @@ import { describe, expect, test } from "bun:test"
 import type { UserMessage } from "@opencode-ai/sdk/v2"
 import { resetSessionModel, syncSessionModel } from "./session-model-helpers"
 
-const message = (input?: Partial<Pick<UserMessage, "agent" | "model" | "variant">>) =>
+const message = (input?: Partial<Pick<UserMessage, "agent" | "model" | "variant" | "fast">>) =>
   ({
     id: "msg",
     sessionID: "session",
@@ -31,6 +31,24 @@ describe("syncSessionModel", () => {
 
     expect(calls).toEqual([message({ variant: "high" })])
   })
+
+  test("restores fast mode from the last message", () => {
+    const calls: unknown[] = []
+
+    syncSessionModel(
+      {
+        session: {
+          restore(value) {
+            calls.push(value)
+          },
+          reset() {},
+        },
+      },
+      message({ fast: true }),
+    )
+
+    expect(calls).toEqual([message({ fast: true })])
+  })
 })
 
 describe("resetSessionModel", () => {
diff --git a/packages/app/src/pages/session/use-session-commands.tsx b/packages/app/src/pages/session/use-session-commands.tsx
index 1a2e777f52..ed31a248d4 100644
--- a/packages/app/src/pages/session/use-session-commands.tsx
+++ b/packages/app/src/pages/session/use-session-commands.tsx
@@ -353,6 +353,14 @@ export const useSessionCommands = (actions: SessionCommandContext) => {
         slash: "model",
         onSelect: () => dialog.show(() => <DialogSelectModel model={local.model} />),
       }),
+      modelCommand({
+        id: "model.fast.toggle",
+        title: language.t(local.model.fast.current() ? "command.model.fast.disable" : "command.model.fast.enable"),
+        description: language.t("command.model.fast.description"),
+        slash: "fast",
+        disabled: !local.model.fast.available(),
+        onSelect: () => local.model.fast.toggle(),
+      }),
       mcpCommand({
         id: "mcp.toggle",
         title: language.t("command.mcp.toggle"),
diff --git a/packages/app/src/testing/model-selection.ts b/packages/app/src/testing/model-selection.ts
index a5ea199ac1..2dae0e3454 100644
--- a/packages/app/src/testing/model-selection.ts
+++ b/packages/app/src/testing/model-selection.ts
@@ -7,20 +7,23 @@ type State = {
   agent?: string
   model?: ModelKey | null
   variant?: string | null
+  fast?: boolean
 }
 
 export type ModelProbeState = {
   dir?: string
   sessionID?: string
   last?: {
-    type: "agent" | "model" | "variant"
+    type: "agent" | "model" | "variant" | "fast"
     agent?: string
     model?: ModelKey | null
     variant?: string | null
+    fast?: boolean
   }
   agent?: string
   model?: (ModelKey & { name?: string }) | undefined
   variant?: string | null
+  fast?: boolean
   selected?: string | null
   configured?: string
   pick?: State
diff --git a/packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx b/packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx
index c85426cc24..1685f0df6b 100644
--- a/packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx
+++ b/packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx
@@ -164,7 +164,8 @@ export function Prompt(props: PromptProps) {
       if (msg.agent && isPrimaryAgent) {
         local.agent.set(msg.agent)
         if (msg.model) local.model.set(msg.model)
-        if (msg.variant) local.model.variant.set(msg.variant)
+        local.model.variant.set(msg.variant)
+        local.model.fast.set(msg.fast === true)
       }
     }
   })
@@ -330,6 +331,19 @@ export function Prompt(props: PromptProps) {
           input.cursorOffset = Bun.stringWidth(content)
         },
       },
+      {
+        title: local.model.fast.current() ? "Disable fast mode" : "Enable fast mode",
+        value: "model.fast",
+        category: "Model",
+        enabled: local.model.fast.available(),
+        slash: {
+          name: "fast",
+        },
+        onSelect: (dialog) => {
+          local.model.fast.toggle()
+          dialog.clear()
+        },
+      },
       {
         title: "Skills",
         value: "prompt.skills",
@@ -586,6 +600,7 @@ export function Prompt(props: PromptProps) {
     // Capture mode before it gets reset
     const currentMode = store.mode
     const variant = local.model.variant.current()
+    const fast = local.model.fast.current()
 
     if (store.mode === "shell") {
       sdk.client.session.shell({
@@ -621,6 +636,7 @@ export function Prompt(props: PromptProps) {
         model: `${selectedModel.providerID}/${selectedModel.modelID}`,
         messageID,
         variant,
+        fast,
         parts: nonTextParts
           .filter((x) => x.type === "file")
           .map((x) => ({
@@ -637,6 +653,7 @@ export function Prompt(props: PromptProps) {
           agent: local.agent.current().name,
           model: selectedModel,
           variant,
+          fast,
           parts: [
             {
               id: PartID.ascending(),
@@ -765,6 +782,8 @@ export function Prompt(props: PromptProps) {
     return !!current
   })
 
+  const showFast = createMemo(() => local.model.fast.current())
+
   const placeholderText = createMemo(() => {
     if (props.sessionID) return undefined
     if (store.mode === "shell") {
@@ -1028,6 +1047,12 @@ export function Prompt(props: PromptProps) {
                       <span style={{ fg: theme.warning, bold: true }}>{local.model.variant.current()}</span>
                     </text>
                   </Show>
+                  <Show when={showFast()}>
+                    <text fg={theme.textMuted}>·</text>
+                    <text>
+                      <span style={{ fg: theme.info, bold: true }}>fast</span>
+                    </text>
+                  </Show>
                 </box>
               </Show>
             </box>
diff --git a/packages/opencode/src/cli/cmd/tui/context/local.tsx b/packages/opencode/src/cli/cmd/tui/context/local.tsx
index d93079f12a..5a15177075 100644
--- a/packages/opencode/src/cli/cmd/tui/context/local.tsx
+++ b/packages/opencode/src/cli/cmd/tui/context/local.tsx
@@ -13,6 +13,7 @@ import { useArgs } from "./args"
 import { useSDK } from "./sdk"
 import { RGBA } from "@opentui/core"
 import { Filesystem } from "@/util/filesystem"
+import * as Fast from "@/provider/fast"
 
 export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
   name: "Local",
@@ -112,12 +113,14 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
           modelID: string
         }[]
         variant: Record<string, string | undefined>
+        fast: Record<string, boolean | undefined>
       }>({
         ready: false,
         model: {},
         recent: [],
         favorite: [],
         variant: {},
+        fast: {},
       })
 
       const filePath = path.join(Global.Path.state, "model.json")
@@ -135,6 +138,7 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
           recent: modelStore.recent,
           favorite: modelStore.favorite,
           variant: modelStore.variant,
+          fast: modelStore.fast,
         })
       }
 
@@ -143,6 +147,7 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
           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.fast === "object" && x.fast !== null) setModelStore("fast", x.fast)
         })
         .catch(() => {})
         .finally(() => {
@@ -358,6 +363,36 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
             this.set(variants[index + 1])
           },
         },
+        fast: {
+          selected() {
+            const m = currentModel()
+            if (!m) return false
+            const key = `${m.providerID}/${m.modelID}`
+            return modelStore.fast[key] === true
+          },
+          current() {
+            return this.selected() && this.available()
+          },
+          available() {
+            const m = currentModel()
+            if (!m) return false
+            const provider = sync.data.provider.find((x) => x.id === m.providerID)
+            const info = provider?.models[m.modelID]
+            if (!info) return false
+            return Fast.enabled(info, { codex: info.providerID === "openai" })
+          },
+          set(value: boolean) {
+            const m = currentModel()
+            if (!m) return
+            if (value && !this.available()) return
+            const key = `${m.providerID}/${m.modelID}`
+            setModelStore("fast", key, value || undefined)
+            save()
+          },
+          toggle() {
+            this.set(!this.current())
+          },
+        },
       }
     })
 
diff --git a/packages/opencode/src/provider/fast.ts b/packages/opencode/src/provider/fast.ts
new file mode 100644
index 0000000000..a344a63ac4
--- /dev/null
+++ b/packages/opencode/src/provider/fast.ts
@@ -0,0 +1,45 @@
+type Model = {
+  providerID: string
+  api: {
+    id: string
+    npm: string
+  }
+}
+
+function lower(model: Pick<Model, "api">) {
+  return model.api.id.toLowerCase()
+}
+
+type Input = {
+  codex?: boolean
+}
+
+export function kind(model: Pick<Model, "providerID" | "api">, input?: Input) {
+  const id = lower(model)
+  if (
+    model.providerID === "anthropic" &&
+    model.api.npm === "@ai-sdk/anthropic" &&
+    (id.includes("claude-opus-4-6") || id.includes("claude-opus-4.6") || id.includes("opus-4-6"))
+  ) {
+    return "claude"
+  }
+  if (
+    model.providerID === "openai" &&
+    input?.codex === true &&
+    model.api.npm === "@ai-sdk/openai" &&
+    id.includes("gpt-5.4")
+  ) {
+    return "codex"
+  }
+}
+
+export function enabled(model: Pick<Model, "providerID" | "api">, input?: Input) {
+  return !!kind(model, input)
+}
+
+export function options(model: Pick<Model, "providerID" | "api">, input?: Input) {
+  const mode = kind(model, input)
+  if (mode === "claude") return { speed: "fast" }
+  if (mode === "codex") return { serviceTier: "priority" }
+  return {}
+}
diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index 05b9f031fe..75a8b0370d 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -6,6 +6,7 @@ import type { Provider } from "./provider"
 import type { ModelsDev } from "./models"
 import { iife } from "@/util/iife"
 import { Flag } from "@/flag/flag"
+import * as Fast from "./fast"
 
 type Modality = NonNullable<ModelsDev.Model["modalities"]>["input"][number]
 
@@ -905,6 +906,10 @@ export namespace ProviderTransform {
     return { [key]: options }
   }
 
+  export function fast(model: Provider.Model, input?: { codex?: boolean }) {
+    return Fast.options(model, input)
+  }
+
   export function maxOutputTokens(model: Provider.Model): number {
     return Math.min(model.limit.output, OUTPUT_TOKEN_MAX) || OUTPUT_TOKEN_MAX
   }
diff --git a/packages/opencode/src/session/compaction.ts b/packages/opencode/src/session/compaction.ts
index 8d934c05da..6342132d33 100644
--- a/packages/opencode/src/session/compaction.ts
+++ b/packages/opencode/src/session/compaction.ts
@@ -141,6 +141,7 @@ export namespace SessionCompaction {
       mode: "compaction",
       agent: "compaction",
       variant: userMessage.variant,
+      fast: userMessage.fast,
       summary: true,
       path: {
         cwd: Instance.directory,
diff --git a/packages/opencode/src/session/llm.ts b/packages/opencode/src/session/llm.ts
index 4e42fb0d2e..5479ee8bb2 100644
--- a/packages/opencode/src/session/llm.ts
+++ b/packages/opencode/src/session/llm.ts
@@ -101,11 +101,15 @@ export namespace LLM {
           sessionID: input.sessionID,
           providerOptions: provider.options,
         })
+    const fast = (
+      input.small || !input.user.fast ? {} : ProviderTransform.fast(input.model, { codex: isCodex })
+    ) as Record<string, any>
     const options: Record<string, any> = pipe(
-      base,
-      mergeDeep(input.model.options),
-      mergeDeep(input.agent.options),
-      mergeDeep(variant),
+      base as Record<string, any>,
+      mergeDeep(input.model.options as Record<string, any>),
+      mergeDeep(input.agent.options as Record<string, any>),
+      mergeDeep(variant as Record<string, any>),
+      mergeDeep(fast),
     )
     if (isCodex) {
       options.instructions = SystemPrompt.instructions()
diff --git a/packages/opencode/src/session/message-v2.ts b/packages/opencode/src/session/message-v2.ts
index 8e4babd619..23d4d901c6 100644
--- a/packages/opencode/src/session/message-v2.ts
+++ b/packages/opencode/src/session/message-v2.ts
@@ -369,6 +369,7 @@ export namespace MessageV2 {
     system: z.string().optional(),
     tools: z.record(z.string(), z.boolean()).optional(),
     variant: z.string().optional(),
+    fast: z.boolean().optional(),
   }).meta({
     ref: "UserMessage",
   })
@@ -437,6 +438,7 @@ export namespace MessageV2 {
     }),
     structured: z.any().optional(),
     variant: z.string().optional(),
+    fast: z.boolean().optional(),
     finish: z.string().optional(),
   }).meta({
     ref: "AssistantMessage",
diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index 743537f598..5612d6ba81 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -111,6 +111,7 @@ export namespace SessionPrompt {
     format: MessageV2.Format.optional(),
     system: z.string().optional(),
     variant: z.string().optional(),
+    fast: z.boolean().optional(),
     parts: z.array(
       z.discriminatedUnion("type", [
         MessageV2.TextPart.omit({
@@ -363,6 +364,7 @@ export namespace SessionPrompt {
           mode: task.agent,
           agent: task.agent,
           variant: lastUser.variant,
+          fast: lastUser.fast,
           path: {
             cwd: Instance.directory,
             root: Instance.worktree,
@@ -575,6 +577,7 @@ export namespace SessionPrompt {
           mode: agent.name,
           agent: agent.name,
           variant: lastUser.variant,
+          fast: lastUser.fast,
           path: {
             cwd: Instance.directory,
             root: Instance.worktree,
@@ -984,6 +987,7 @@ export namespace SessionPrompt {
       system: input.system,
       format: input.format,
       variant,
+      fast: input.fast,
     }
     using _ = defer(() => InstructionPrompt.clear(info.id))
 
@@ -1310,6 +1314,7 @@ export namespace SessionPrompt {
         model: input.model,
         messageID: input.messageID,
         variant: input.variant,
+        fast: input.fast,
       },
       {
         message: info,
@@ -1727,6 +1732,7 @@ NOTE: At any point in time through this workflow you should feel free to ask the
     arguments: z.string(),
     command: z.string(),
     variant: z.string().optional(),
+    fast: z.boolean().optional(),
     parts: z
       .array(
         z.discriminatedUnion("type", [
@@ -1884,6 +1890,7 @@ NOTE: At any point in time through this workflow you should feel free to ask the
       agent: userAgent,
       parts,
       variant: input.variant,
+      fast: input.fast,
     })) as MessageV2.WithParts
 
     Bus.publish(Command.Event.Executed, {
diff --git a/packages/opencode/test/provider/transform.test.ts b/packages/opencode/test/provider/transform.test.ts
index 917d357eaf..e5037e36b3 100644
--- a/packages/opencode/test/provider/transform.test.ts
+++ b/packages/opencode/test/provider/transform.test.ts
@@ -176,6 +176,70 @@ describe("ProviderTransform.options - gpt-5 textVerbosity", () => {
   })
 })
 
+describe("ProviderTransform.fast", () => {
+  const createModel = (input: { providerID: string; modelID: string; npm: string }) =>
+    ({
+      id: input.modelID,
+      providerID: input.providerID,
+      api: {
+        id: input.modelID,
+        url: "https://example.com",
+        npm: input.npm,
+      },
+      name: input.modelID,
+      capabilities: {
+        temperature: true,
+        reasoning: true,
+        attachment: true,
+        toolcall: true,
+        input: { text: true, audio: false, image: true, video: false, pdf: false },
+        output: { text: true, audio: false, image: false, video: false, pdf: false },
+        interleaved: false,
+      },
+      cost: { input: 0, output: 0, cache: { read: 0, write: 0 } },
+      limit: { context: 200000, output: 8192 },
+      status: "active",
+      options: {},
+      headers: {},
+    }) as any
+
+  test("uses speed fast for anthropic opus 4.6", () => {
+    const model = createModel({
+      providerID: "anthropic",
+      modelID: "claude-opus-4-6",
+      npm: "@ai-sdk/anthropic",
+    })
+    expect(ProviderTransform.fast(model)).toEqual({ speed: "fast" })
+  })
+
+  test("uses priority service tier for openai gpt-5 codex models", () => {
+    const model = createModel({
+      providerID: "openai",
+      modelID: "gpt-5.4",
+      npm: "@ai-sdk/openai",
+    })
+    expect(ProviderTransform.fast(model, { codex: true })).toEqual({ serviceTier: "priority" })
+  })
+
+  test("returns empty options for unsupported models", () => {
+    const model = createModel({
+      providerID: "anthropic",
+      modelID: "claude-sonnet-4-6",
+      npm: "@ai-sdk/anthropic",
+    })
+    expect(ProviderTransform.fast(model)).toEqual({})
+  })
+
+  test("returns empty options for openai api mode", () => {
+    const model = createModel({
+      providerID: "openai",
+      modelID: "gpt-5.4",
+      npm: "@ai-sdk/openai",
+    })
+    expect(ProviderTransform.fast(model)).toEqual({})
+  })
+})
+
 describe("ProviderTransform.options - gateway", () => {
   const sessionID = "test-session-123"
 
diff --git a/packages/sdk/js/src/v2/gen/sdk.gen.ts b/packages/sdk/js/src/v2/gen/sdk.gen.ts
index 27c188838b..97fa44f6f3 100644
--- a/packages/sdk/js/src/v2/gen/sdk.gen.ts
+++ b/packages/sdk/js/src/v2/gen/sdk.gen.ts
@@ -1841,6 +1841,7 @@ export class Session2 extends HeyApiClient {
       format?: OutputFormat
       system?: string
       variant?: string
+      fast?: boolean
       parts?: Array<TextPartInput | FilePartInput | AgentPartInput | SubtaskPartInput>
     },
     options?: Options<never, ThrowOnError>,
@@ -1861,6 +1862,7 @@ export class Session2 extends HeyApiClient {
             { in: "body", key: "format" },
             { in: "body", key: "system" },
             { in: "body", key: "variant" },
+            { in: "body", key: "fast" },
             { in: "body", key: "parts" },
           ],
         },
@@ -1973,6 +1975,7 @@ export class Session2 extends HeyApiClient {
       format?: OutputFormat
       system?: string
       variant?: string
+      fast?: boolean
       parts?: Array<TextPartInput | FilePartInput | AgentPartInput | SubtaskPartInput>
     },
     options?: Options<never, ThrowOnError>,
@@ -1993,6 +1996,7 @@ export class Session2 extends HeyApiClient {
             { in: "body", key: "format" },
             { in: "body", key: "system" },
             { in: "body", key: "variant" },
+            { in: "body", key: "fast" },
             { in: "body", key: "parts" },
           ],
         },
@@ -2026,6 +2030,7 @@ export class Session2 extends HeyApiClient {
       arguments?: string
       command?: string
       variant?: string
+      fast?: boolean
       parts?: Array<{
         id?: string
         type: "file"
@@ -2051,6 +2056,7 @@ export class Session2 extends HeyApiClient {
             { in: "body", key: "arguments" },
             { in: "body", key: "command" },
             { in: "body", key: "variant" },
+            { in: "body", key: "fast" },
             { in: "body", key: "parts" },
           ],
         },
diff --git a/packages/sdk/js/src/v2/gen/types.gen.ts b/packages/sdk/js/src/v2/gen/types.gen.ts
index 9ab71bd8f5..a03e82c493 100644
--- a/packages/sdk/js/src/v2/gen/types.gen.ts
+++ b/packages/sdk/js/src/v2/gen/types.gen.ts
@@ -238,6 +238,7 @@ export type UserMessage = {
     [key: string]: boolean
   }
   variant?: string
+  fast?: boolean
 }
 
 export type ProviderAuthError = {
@@ -340,6 +341,7 @@ export type AssistantMessage = {
   }
   structured?: unknown
   variant?: string
+  fast?: boolean
   finish?: string
 }
 
@@ -3284,6 +3286,7 @@ export type SessionPromptData = {
     format?: OutputFormat
     system?: string
     variant?: string
+    fast?: boolean
     parts: Array<TextPartInput | FilePartInput | AgentPartInput | SubtaskPartInput>
   }
   path: {
@@ -3484,6 +3487,7 @@ export type SessionPromptAsyncData = {
     format?: OutputFormat
     system?: string
     variant?: string
+    fast?: boolean
     parts: Array<TextPartInput | FilePartInput | AgentPartInput | SubtaskPartInput>
   }
   path: {
@@ -3526,6 +3530,7 @@ export type SessionCommandData = {
     arguments: string
     command: string
     variant?: string
+    fast?: boolean
     parts?: Array<{
       id?: string
       type: "file"